It’s quite difficult to define, but we usually think of the whole process - the whole ‘course

of evolution’ starting with the origin of life and ending with the current biodiversity- and of
course there must have been extinctions along the way.

In the process of evolution the following has happened

 New species arising
 The biodiversity of the planet increasing and
 In general as evolution has progressed, there has been a general trend towards larger and
more complex organisms.
 Figure 4.1 A summary of the course of evolution

For new species to appear, groups of organisms - population - have to change not just
single organism. For them to change, their genes must change, as the genes define what
they will be by controlling protein synthesis. Therefore the process of evolution can be
stated as the change in genetic composition of a population over successive generations,
which may be caused meiosis, hybridization, natural selection or mutation. This leads to a
sequence of events by which the population diverges from other populations of the same
species and may lead to the origin of a new species.

 What theories are there about the Origin of Life on Earth?

There are five main theories of the origin of life on Earth
 Special creationism
 Spontaneous generation
 Eternity of life
 Cosmozoan theory
 Biochemical origin

 How does special creationism account for the origin of life?

The special creationism theory about the origin of life is nearly always linked to religion,
whereas the acceptance of evolution is linked to scientific thinking. Science describes the
natural world around us using a means of observation and empirical testing using
instruments. These observations then result in the development of scientific theories.
Religion mainly focuses on spiritual matters that, by their very nature, cannot be seen,
touched or measured effectively.

Religion
 deals with philosophical matter that relates to morality and concerns between human and
their God
 Is less concerned with empirical observable facts and testable hypotheses but rather with
faith, the belief on things that cannot be proven.

In general, science relies on provable events; religion relies on believing in that which
cannot be proven. Special creation states that at some stage, some supreme being created
life on Earth. There are many different versions of special creation, linked with different
religions:
 Young earth creationism
 Old earth creationism
 Day-age and gap creationism

 Progressive creationism
 Theistic evolution/ Evolutionary creationism
 Intelligent design
A. Young Earth Creationism
 Suggests the earth is only a few thousand years old
 Often believe that the earth was created in six 24-hour days
 Agree that the earth is round and moves around the sun
 Interpret all geology in the light of Noah’s flood
B. Old Earth Creationism
They are several types and vary in different aspects of how they explain the age of the earth
while still holding to the story found in Genesis. Those who believed in old earth
creationism accept the evidence that the earth is very old but still maintain that all life was
created by God.

C. Day-age and gap creationism

These are similar in that each interprets the beginning of the creation story as actually
having taken much longer than six earth days.

Gap creation discusses a large gap between the formation of the earth and the creation of all
the animals and humans. The gap could be millions or billions of years. This gets around the
scientific evidence that the earth is several billion years old without having to believe in the
process of evolution itself.
Day-age creationism is similar in the length of time but talks about each of the six ‘days’ as
really meaning a billion years or so of geologic time the six ‘days’ are just symbolic.

D. Progressive Creationism
This type of creationism accepts the Big Bang as the origin of the universe. It accepts the
fossil record of a series of creations for all of the organisms catalogued. However, it does
not accept these as part of a continuing process; each is seen as a unique creation. Modern
species are not seen as being genetically related to the ancient ones.

E. Theistic Evolution/ Evolutionary Creationism

This view of Evolution:
 Maintains that God ‘invented’ evolution and takes some form of an active part on the
ongoing process of evolution.
 Abo invokes the role of God in areas not discussed by science, like the creation of the
human soul.

 Promoted by the pope for the Catholic Church and also espoused by most maintain
Protestants.

F. Intelligent Design
 This is the newest version of creationism and maintains that God’s handiwork can be
seen in all of creation if one knows where to look.
 Advocates of intelligent design offer sophisticated arguments, often based on cell
biology and mathematics, to give impression of complex scientific arguments and to
create equal stature with mainstream scientific thoughts.
 The term intelligent design is used to mask the fact that it’s a form of creationism
cloaked in scientific sounding ideas.

 How does spontaneous generation seek to Explain Life on Earth?

Spontaneous generation suggests that life can evolve ‘spontaneously’ from non-living
objects. It was only a few hundred years ago that people still believed this to be true.
Figure 4.2 Examples of spontaneous generation. A) Muddy soil gave rise to the frogs B)
Mice came from the moldy grain C) Sewage and garbage turned in to the rats and D)
Rotting meat turned into flies.

The work of Francisco Redi disprove the idea of rotting meat producing flies and the work
of Louis Pasteur to finally show that not even micro-organisms could be produced by
spontaneous generation.

Figure 4.3 Redi’s Experiment

In Redi’s experiment illustrated in figure 4.3, flies only appeared in the jars where flies had
access in the first place. Exclude the flies, as he did with some jars, and the meat does not
produce either maggot or flies.
Louis Pasteur showed that broth (or wine) only went sour if micro-organisms were allowed
to enter. Also no micro-organisms appeared in the broth unless they were allowed to enter
from the outside-they were not formed from the broth itself.

Figure 4.4 Louis Pasteur finally disproves spontaneous generation

These two scientists showed that both macro organism (Redi) and micro-organisms (Louis
Pasteur) can only arise from pre-existing organisms, disproving the theory of spontaneous
generation.

But what about the first ever cell? Unless we believe that life is eternal, with no beginning
and no end, there had to be a first cell. And it could not have come from a pre-existing cell
because it was the first.

Scientists have proposed a method whereby the necessary components of life could be
formed and believe that, somehow they managed to assemble themselves into a primitive
cell. This is a kind spontaneous generation.

 How does the eternity of Life theory seek to explain Life on Earth?

 In this theory of life, there is no beginning and no end to life on Earth and so it
neither needs special creation nor does it need to be generated from non-living
matter.

 Supporters of this theory believe that life is an inherent property of the universe and has
always existed-as has the universe. At the time when such theories were being
 propounded, many eminent scientists-including Albert Einstein-believed that the
universe was unchanging. They reasoned that ‘if life is found today in unchanging
universe, then it must always have been there’.

 How does the cosmozoan theory seek to explain life on Earth?

 According to this theory, life has reached this planet Earth from other cosmological
structures, such as meteorites, in the form of highly resistant spores.

Figure 4.5 Did meteorites bring life to Earth?

 The idea of cosmozoan theory was proposed by Richter in 1865 and supported by
Arrhenius in 1908 and by other contemporary scientists. The theory did not gain any
significant support as it lacks evidence. It strongly linked to the ‘eternity of life’ theory
of the origin of life on Earth.

 In the 19th C, Hermann Richter put forward the idea that life has always existed in the
universe, propagating itself from one place to another by means of ‘Cosmozoa’ (germs
of the cosmos). In this theory, life has existed and will exist for all eternity across the
universe, and so there is no need for an explanation of its origin. Two other eminent
scientists of the time- Lord Kelvin and Herman Von Helmholtz-also took the same
view.

 In 1908, the Swedish physical chemist Svante Arrhenius put forward a new version of
the cosmozoan theory, and gave it the name Panspermia.

 Arrhenius contribution was a new theory of the mechanism by which life could be
transported between planets; he proposed that bacterial spores were propelled through
inter-planetary space by radiation pressure.
 Cosmozoan theory had assumed transport was by means of meteorites or by comets.
However, the very high temperatures that meteorites create on entering the Earth’s
atmosphere seemed to rule this out.

 In Arrhenius version of the theory, spores arriving at the Earth (possibly attached to
grains of interstellar dust) could fall slowly to the ground without being subjected to
high temperatures due to air friction.

 One of the motivations for Arrhenius panspermia theory was that it also seemed to
provide a solution to disproof by Louis pasture’s Experiments of spontaneous
generation in bacteria. Arrhenius theory was dropped by most scientists when it became
apparent that the bacterial spores would be subject to UV radiation and X-radiation,
zones of charged particles which would inevitably destroy them.

However, another version of the cosmozoan theory or panspermia does have some evidence
to back it up. This version-called weak panspermia or pseudo-panspermia-is the theory
that organic compounds arrived from outer space and added to the chemicals on earth that
give rise to the first life.

In 1969 a meteorite landed in Australia that was 12% water and contained traces of 18
amino acids. This evidence points not only the presence of organic compounds in outer
space, but also to the capacity of such compounds to reach Earth. Complex organic
molecules have been detected in star-forming clouds, further adding to the evidence for
organic molecules in space.

The steady state theory of the universe is strongly linked to the eternity of life theory for
scientists now generally accept that the universe began with a ‘Big Bang’ and will either
expand forever or will eventually contract again, ending in a ‘Big Crunch’. However, for the
early part of the 20th C, a number of eminent astronomers and physicists believed that the
universe was in a steady state’. It had always existed the way it was and always would.
 Figure 4.6 Clouds of inter-stellar gas have been shown to contain
organic molecules.

 How does the biochemical theory seek to Explain Life on Earth?

This theory states that the first form of life evolved from a set of chemicals formed as a
result of biochemical reactions. The theory is sometimes called as abiogenesis which owe to
two biologists working early in the twentieth century.

The two Biologists who put forward ideas about abiogenesis are:
 Aleksandar Oparin (in 1924), a Russian Biologist
 John Haldane (in 1929), an English biologist.
These two biologists suggested that:
 The primitive atmosphere of the Earth was a reducing atmosphere with no free oxygen-
as opposed to the oxygen rich atmosphere of today.
 There was an appropriate supply of energy such as lightening or ultraviolet light and
this would provide the energy for reactions that would synthesize a wide range of
organic compounds, such as amino acids, sugar and fatty acids.

Oparin suggested that:

 The simple organic compounds could have undergone a series of reactions leading to
more and more complex molecules.
 The molecules have might have formed colloidal aggregates, or‘coacervates’ in an
aqueous environment.

 The coacervates were able to absorb and assimilate organic compounds from the
environment in a way similar to the metabolism of cells.

These coacervates were the precursors of cells and would be subject to natural selection,
eventually leading to the first true cells. Figure 4.7 below shows some coacervate droplets
containing amino acids and small polymers of one of the nitrogenous bases in DNA.
 Figure 4.7 Coacervate droplets – pre-cells?

Haldane proposed similarly that:-

 The primitive sea served as a vast chemical laboratory powered by solar energy.
 As a result of all the reactions powered by solar energy, the sea becomes a ‘hot dilute
soup’ of organic monomers and small polymers.
 He called this soup the ‘prebiotic soup’, and this came to symbolize the Oparin-
Haldane view of the origin of life.

As an evidence for the theory:

In 1953, Stanley Miller conducted his now-famous spark-discharge experiment. In this
investigation, he passed electric sparks repeatedly through a mixture of gases that were thought
to represent the primitive atmosphere of the Earth. These gases were

 Methane (CH4) * water(H2O) and

 Ammonia (NH3) * hydrogen (H2)
 Figure 4.8 Stanley Miller’s spark-discharge experiment

When he analyzed the liquid in the water trap, he found it contained a number of simple
organic molecules-hydrogen cyanide (HCN) was one of them. He found that by leaving the
equipment for longer periods of time, a larger variety and more complex organic molecules
were formed including:

 Amino acids-essential to form proteins

 Pentose sugars- needed to form nucleic acids
 Hexose sugars-needed for respiration and to form starch and cellulose
 Hydrogen cyanide- the nitrogenous bases found in nucleotides can be synthesized in the
laboratory using HCN as a starting point.

The Oparin- Haldane hypothesis has been supported by considerable evidence but with its
problems. These include:

 Why are only ‘Left handed’ amino acids found in living things when both Left-handed
and right-handed type are possible?
 Although nitrogenous bases can be synthesized in the laboratory, purines (adenine and
guanine) are not synthesized under the same conditions as pyrimidine (thymine, Uracil
and cytosine); this is quite a series problem for the theory.
 Although Miller was able to demonstrate the formation of monomers in his
investigation, he was unable to demonstrate the next significant step of polymerization
of these monomers.
In 2009, John Sutherland, a chemist at the University of Manchester in England, found that,
instead of making the nitrogenous base and sugar separately from chemicals likely to have
existed on the primitive earth, under the right conditions the base sugar could be built up as
a single unit (a nucleotide) and so did not need to be linked. It has been shown that
polymerization can occur under appropriate conditions and a solution is in sight for the
‘handedness’ problem.

John Desmond Bernal suggested that there were a number of clearly defined ‘stages’ in
explaining the origin of life.

 Stage 1= the origin of biological monomers

 Stage 2= the origin of biological polymers
 Stage 3= the evolution from molecules to cell

Bernal suggested that evolution may have commenced at sometime between stage 1 and
2.The first two stages have been demonstrated as being possible in the conditions of the
primitive earth, and research on stage 3 is well advanced.

How did Autotrophs Evolve on Earth?

Paleontological evidences suggest that the first forms of life were heterotrophic
prokaryotes which were also anaerobic, respiring without oxygen. These were dependent
on the organic molecules which had accumulated in the seas. Later, the organic molecules
were depleted. In the depleted organic compound environment, only organisms that could
synthesize organic compounds could survive. These were the autotrophs, either
chemosynthetic or photosynthetic.
Prokaryotes were the first organism appeared about 4 billion years ago. They had no true
nucleus. They had RNA rather than DNA as their genetic material. They gave rise to three
distinct lines of evolution leading to:

 Archeabacteria- prokaryotes including thermophilic sulphobacteria, methanobacteria

and halophilic bacteria
 Eubacteria- prokaryotes; ordinary bacteria and cyanobacteria (blue-green bacteria and
sometimes known as blue green algae).
 Eukarystes- eventually evolving into protoctistans, fungi, plants, animals (nearly all
are aerobic)
One great change that affected the evolution of early life forms was the shift from the
reducing atmosphere to an atmosphere containing oxygen. This took place about 2.4 billion
years ago. Where did this oxygen come from? There is only one process we know of that
can have produced it- photosynthesis.
Archaebacteria are found in extreme conditions:
 Thermophilic means “heat loving” and these bacteria are found at temperatures that
would kill other cells
 Methanobacteria- bacteria that can live in high concentrations of methane
 Halophilic bacteria- those bacteria that live at high salt concentrated area

The fossil record shows that cyanobacteria had been producing oxygen by photosynthesis
from about 3.5 billion years ago but that for almost 1 billion years the levels in the
atmosphere did not rise because the oxygen was absorbed by the vast among of iron in the
earth-it rusted!! But by 2.4 billion years ago, the concentration began to rise and the rate of
increase accelerated from 2.1 billion years ago.

Figure 4.9 Cyanobacteria have been around for a long time

Cyano-bacteria are photo-autotrophs. They use light as a source of energy, and CO2 as
source of carbon (photosynthesis). They are among the earliest of autotrophs using, not
chlorophyll, but another pigment, phycocyanin (which gives them their blue-green
appearance), to capture light energy.
 Figure 4.10 Phycocyanin absorbs different wavelengths of light from
chlorophyll

Other primitive autotrophs used not light as source of energy but chemical reactions and are
called chemo-autotrophs. Chemo-autotrophs use the energy from chemical reactions to
synthesis all necessary organic compounds, starting from carbon dioxide. They generally
only use inorganic energy sources. Most are bacteria or archea that live in hostile
environments such as deep sea vents and are primary producers in ecosystems on the sea
beds.

The primitive sulphobacteria use hydrogen sulphide as the energy source.

Hydrothermalism, particularly in deep sea vents, maintains the bacterial life of
sulphobacteria and/or methanobacteria.

 Bacteria are the only life forms found in the rocks for a long time, 3.5 to 2.1 billion
years ago.
 Eukaryotes become numerous 1.9 to 2.1 billion years ago and
 Fungi- like organisms appeared about 0.9 billion years ago.

The oxygen produced by the photo-autotrophs had made it possible for aerobic respiration
to evolve as an energy releasing pathway. As this process release far more energy than does
the anaerobic pathway more active organisms could now evolve-the animals, perhaps 600 to
700 million years ago.
 Figure 4.11 Life on Earth has evolved over billions of years

Evolution is the change in genetic composition of a population over successive generations,

which may be caused by meiosis, hybridization, natural selection of mutation. This leads to
a sequence of events by which the population diverges from other populations of the same
species and may lead to the origin of a new species.

But how does this happen? What drives the population to become a new species? Among
many more theories Charles Darwin (natural selection), who put forward the idea to the
Royal society in 1858, suggested that those organisms that were best adapted to their
environment would have an advantage and be able to reproduce in greater numbers than
other types, and pass on the advantageous adaptations. Because he knew nothing of genetic,
he was unable to suggest how this takes place.

For many years in Europe, the christen belief had been that the Earth and all species had
been created about 6000 years ago. In the mid-1700s, George Buffon challenged this idea,
suggesting that:

 The earth was much older than this and

 Organisms changed over time in response to environmental pressures and random
events.
At the start of 19th Century, Lamarck made the first major advance towards modern
evolutionary thinking because he proposed a mechanism by which the gradual change in
species might take place.

In 1809, he published a paper entitled ‘Philosophie Zoologique’, in which he described a

two part mechanism by which change was gradually introduced into the species and passed
down through generations. His theory is called the ‘theory of transformation’ or, more
usually, simply ‘Lamarckism’. The two parts of his theory are:

 Use and disuse, and

 Inheritance of acquired traits

Use and Disuse

Lamarck suggests that by continually using a structure or process, that structures or process
will become enlarged or more developed. Conversely, any structure or process that is not
used or is little used will become reduced in size or less developed. The classic example he
used to explain the concept of use and disuse is the elongated neck of the giraffe.

Figure 4.12 Lamarck’s idea of use and disuse and the inheritance of acquired
traits of evolution
According to Lamarck, a given giraffe could, over a life time of straining to reach high
branches, develop an elongated neck. However, Lamarck could not explain how this might
happen. He talks about a natural tendency towards perfection - but this not really an
explanation.
Another example: - The toes of water birds – webbed toes.
Disuse example:-The wings of penguins have become smaller than those of other birds
because penguins do not use them to fly.

Inheritance of Acquired Traits

Lamarck believed that traits changed or acquired during an individual’s lifetime could be
passed on to its offspring. Giraffes that had acquired long necks would have offspring
with long necks rather than the short necks their parents were born with. However,
Lamarck did believe that evolutionary change takes place gradually and constantly.

He studied ancient seashells and noticed that the older they were, the simpler they appeared.
From this, he concluded that species started out simple and consistently moved towards
complexity, or as he termed it, closer to perfection. This idea we still retain today.

50 years later, in 1858, Charles Darwin published his famous paper on Natural selection. In
the same year, another Biologist, Alfred Russell Wallace, had come to similar conclusions
and they jointly published the scientific paper to the Linnaean society of London.

Some of the Darwin’s evidence came from a visit to the GalapagosIslands. Darwin visited
five of the Galapagos Islands and made drawings and collected specimens.

Darwin, particularly studied the finches found on the different islands and noted that there
were many similarities between them, as well as the obvious differences. He concluded that
the simplest explanation was that an ‘ancestral finch’ had colonized the islands from the
mainland and in the absence of predators, been able to adapt to the different conditions on
the islands and eventually evolve in to different species.
 Figure 4.13 Darwin’s finches

Some of the finches had evolved into insect eaters, those with pointed beaks. Others had
evolved into seed eaters with beaks capable of crushing the seeds.

150 years later on and geneticist have been able to confirm Darwin’s ideas and even
produced a ‘family tree based on the similarity of their DNA. Biologists wanted to test how
well the finches were adapted to their ‘niche’. They analyzed the size of the seeds eaten by
the three different ground finches.
 Figure 4.14 The different sizes of seeds eaten by three species of ground finch
from the Galapagos Islands

Although there is a little overlap, as fig 4.14 depicts, each finch eats seeds of a different size
and their beaks are adapted to obtain and crush these different-sized seeds.At the same time,
Darwin called this ‘descent with modification’ and believed it to be key evidence in support
of his theory of natural selection. Now this is called ‘adaptive radiation’.

Natural selection is the process by which individuals, which are well adapted to their
environment, survive. This increases their chances to survive and reproduce. Poorly adapted
individuals die. The theory of natural selection was based on the following observations and
deductions, overproduction, struggle for existence and variation.

1. Overproduction (fecundity). Darwin observed that the number of offspring produced

by a species is greater than the number that survive, reproduce and live to maturity. Most
organisms have a high reproductive rate. However, normally only a few survive and
reproduce.

2. Struggle for existence (competition). The struggle for existence arises largely from
competition. Individuals compete with one another for the limited resources that enable
them to survive such as food, space and light. Limitation of resources would result in a
struggle for existence between individuals of the same species. This kind of struggle is
called intraspecific struggle. If individuals of two different species compete, it is called
interspecific struggle.
3. The survival of the fittest or natural selection. In the struggle for existence only those
individuals that are best suited to new conditions of life will survive. The ones that are
the least fit will be the first to perish. This principle is known as Survival of the fittest.

4. Variation – In any species there is variation between individuals. Some individuals are
better adapted to the environment than others. These individuals will be more likely to
survive than others. They will be most likely to reproduce and pass on their good
characteristics to their offspring.

Altogether Darwin summarized his observations in two main ideas:

 All species tend to produce more offspring than can possibly survive.
 There is variation among the offspring
From these observations he deduced that:
 There will be a ‘struggle for existence’ between members of a species (because they
over-reproduce, and resources are limited)
 Some members of a species with be better adapted to their environment (because
there is variation in their offspring)

Combining these two deductions, Darwin proposed:

Those members of a species which are best adapted to their environment will survive
and reproduce in greater numbers than others less well adapted.
 Table 4.1 Comparison of Lamarck’s theory of use and disuse with Darwin’s theory
of natural selection

Aspect of Lamarck’s theory of use and disuse Darwin’s theory of natural

theory selection
Variation Environmental changes creating a There is a natural variation in
need for the organism to change features and the variations are
heritable
Survival Development of new features (e.g. Environment selects infavor of
longer neck) in order to survive those traits that adapt the orgm
to the environment and against
those that do not
Inheritance New features acquired during lifetime Individuals with advantageous
of an individual are passed to the variations of traits survive in
offspring greater numbers and pass on
these traits to their offspring
Evolution New species over time New species over time

What is neo- Darwinism?

Charles Darwin knew very little of genetics. At the time of Darwin published his book
on the origin of species, Mendel had not carried out his ground breaking work on
inheritance. Genes, or more accurately, alleles of genes determine features. But when
we think about how a population might evolve into a new species, we need to think not
in terms of the alleles each individual might carry, but also in terms of all the alleles (of
all genes) present in the population. That has to think of the gene pool of the population.

Suppose all allele determines a feature that gives an organism an advantage in its
environment. The following will happen
 Those individuals with the advantageous allele of the gene will survive to produce in
greater numbers than other types
 They will pass on their advantageous allele in greater numbers than other type
 The frequency of the advantageous allele in the gene pool of the population will be
higher in the next generation.
 This process repeats over many generations and the frequency of advantageous
allele in the gene pool increases with each generation that passes.

Mutations are important in introducing variation into populations. Any mutation could
produce an allele which:
 Confers a selective advantage; the frequency of the allele will increase over time.
 Is neutral in its overall effect; the frequency may increase slowly, remain stable or
decrease (the change in frequency will depend on what other genes /alleles are
associated with the mutant allele).
 Is advantageous; the frequency of the allele will be low and could disappear from the
population

Neo- Darwinism
 Take into account our knowledge of genetics
 It encompasses our understanding of animal behavior- sometimes referred to as
ethology.
 Many ethologists and evolutionary psychologist believe that behavioral patterns confer
survival advantage than physical features - or not.

E.g. Imprinting in geese

The evidences for evolution are derived from various branches of science. The important
sources of evidence are:
1. Evidence from paleontology (the study of fossils)
2. Evidence from body structure
3. Evidence from comparative embryology
4. Evidence from comparative biochemistry
5. Evidence from plant and animal breeding

How does paleontology support the theory of evolution?

The word ‘paleontology’ refers to the study of ancient life and comes from the Greek words
palaios (ancient) and logos (study). Fossils form the basis of this science as they are the
main direct evidence about past life. Fossils (from Latin word fossus, meaning ‘having been
dug up’) are the remains of animals, plants and other organisms from the remote past. We
can group fossils into two categories:

Category 1: the remains of the dead animals or plant or the imprint left from the remains,
including:
 Bones
 Teeth
 Skin impressions
 Hair
 The hardened shell of an ancientinvertebrate such as a trilobite or an ammonite
 An impression of an animal or plant, even if the actual parts are missing

Category 2: Something that was made by the animal while it was living that has since
hardened into stone; this are called trace fossils and include:

 Footprint
 Burrows
 Coprolite (animal faeces)

B
Figure 4.15 A - Dinosaur’s foot print; B – Dinosaur

Type 1 fossils can be the actual organism or part of the organism, like a piece of bone or
hair or feather as it actually was.
 For example: the spider trapped inside the amber for million years gets completely
unchanged Amber is a fossilized resin from trees. This is because; the spider is protected
from micro-organism within the amber. Amber is fossilized resin from trees.

Figure 4.16 A spider preserved in amber

In many fossils, the soft parts of the body have been lost, but the exoskeleton is perfectly
preserved. In some cases, however, the entire body remains.

There are four main stages in fossil formation: These are

1. Death without decomposition
 An animal or plant die in or so close to water covered immediately after, or shortly after
death.
 The water insulates the remains from many of the elements that contribute to
decomposition.
 Bacteria will still decay the soft body parts over a long period but leave any hard body
parts unaltered.

2. Sedimentation
 As time passes sediments bury the remaining hard parts of the organism.
 Fossilization is more likely if this happens quickly than if it happens more slowly.
 The chemical makeup of the sediments affects the color of the fossil will be.
 The nature of the sediments themselves influences the nature and quality of the fossil
 Iron-rich sediments could give the rock (and the fossil) a reddish color. Phosphates may
darken the rock so that it is grey or black.

3. Permineralisation
As the sediments accumulate, the lower layers become compacted by the weight of the
layers on top. Over time, this pressure turns the sediments into rock. If water rich in
minerals percolates (seeps) through the sediments, the mineral particles stick to the particles
of sediment and effectively glue them together into a solid mass. Over the course of
millions of years, these mineral particles dissolve away the original hard parts of the
organism, replacing the molecules of exoskeleton with molecules of calcite (calcium
carbonate) or another mineral. In time, the entire shell is replaced by mineral particles and
these also are compressed into rock in the shape of the original organism. As this rock is not
the same as the surrounding rock, it is visible as a fossil in the exact shape of the original
organism.

4. Uplift
As continental plates moves around the Earth, colliding with each other, mountains formed
sea floors are lifted up and become dry land.

Figure 4.17 Earth movements may expose rocks that were deep beneath the
surface

How can we date fossils?

Because sedimentary rocks are laid down in layers (strata) we can use the sequence of the
strata and the fossils that occur in them to deduce how the organism have changed overtime,
This is called stratigraphy. The oldest strata is the oldest fossils and will be in the lowest
layers and more recent rocks and fossils in the layer above them, with the most recent being
nearest to the surface.
 Figure 4.18 Stratigraphy allows us to deduce the relative age of fossils

Figure 4.17 shown above depicts, the depth of the strata is related to their age. The thickness
of each stratum is a measure of the time period during which that stratum is formed.

The commonest method used by scientists to determine the ages of rocks and hence fossils
trapped in them is radiometric dating. This method depends on the fact that some isotopes
of certain elements are radioactive. They are unstable and decay at a constant rate. This is
known as radioactive decay. Radioactive parent elements decay to stable daughter elements.
When a molten rock cools and solidifies and radioisotope trapped in the rock will begin to
decay into its daughter elements. Thus, by measuring the amount of parent and daughter
elements in the rock and by determining the rate at which the parent element decays into its
daughter element, the date at which the rock was formed and the fossil was deposited can be
estimated. The rate of decay is expressed in terms of the half – life of that isotope. Half –
life refers to the time taken for the radioactive isotope to fall by half. The shorter the half –
life, the faster is the rate of decay. Examples of radioisotopes commonly used in the
determination of the ages of rocks are carbon – 14, potassium 40 and uranium 235. Note
the number is the mass number.

14
The ratio of C to C12 in living things is about 1, 1x1012(trillion) this has always the same,
12
burring their lives living things lose C14 (as CO2 and other execratory products) and also
gain it in the food they eat (or make it in the case of autotrophs).
 Figure 4.19 Half-life of a radioactive element

But when living things die, the C14start to decay in to non-radioactive nitrogen, and clearly
not replaced. So after 5730 years (one half-life of C14), only 50% of the original carbon 14
atoms will remain and the ratio of C 14 to C12 will be 1 to 2 trillion (or 0.5 to 1 trillion). After
11,460 years, 25% of the original C 14 atoms remain and the ratio is 1 to 4 trillion (or 0.25 to
1 trillion). The percentage of C14 atoms and the ratio of carbon 14 to C12keep having with
each half-life that passes.

Figure 4.20 Converting the percentage of carbon 14 in a fossil to an age

So, if we analyzed a fossil and found that it had only 6.25% of its original C 14 atoms, we
would know that it was 22 920 years old. Potassium- argon dating works in the same way,
but the half-life in this case is 1.3 million years. This makes potassium-argon dating
suitable for dating rocks millions of years old, whereas radio carbon dating is really only
accurate with rocks up to 60,000 years old.
How does Comparative anatomy Support the theory of Evolution?
This is one of the strongest forms of evidence for evolution. Comparative anatomy looks at
structural similarities of organisms and uses these to determine their possible evolutionary
relationships. It assumes that organism with similar anatomical features are closely related
evolutionarily, and that they probably share a common ancestor.

Homologous structure- organisms with similar anatomical structure, but very different in
function best example of homologous structures is the forelimbs of mammals.
 The forelimbs of humans, whales, cats and bats are all very similar in structure.

Figure 4.21 The forelimbs of mammals are homologous structures

Each possesses the same number of bones, arranged in almost the same way, while they
have different external features and they function in different ways and
 Arm for manipulation in humans
 Leg for running in cats
 Flipper for swimming in whales
 Wing for flying in bats

Analogous structures- organisms which are morphologically and developmentally different

but with the same function. These organisms cannot indicate that two species share a
common ancestor.
Example: -The wings of a bird and a mosquito

How does Comparative Embryology Support the theory of Evolution?

Embryology deals with the study of organisms in the early stages of embryonic
development. Research in the late 1800s showed important evidence about evolution. These
were striking
similarities in the embryos of different organisms, making it difficult to distinguish between
embryos of various vertebrate groups in the early stages of their development. The
resemblance of the embryo was not only external but also internal, that is, the arrangement
of the arteries and the structure of the development of the arteries and the structure of the
developing hearts. This development shows similarities which supports a common
ancestory.

For examples, early in development, all vertebrate embryos (including us) have gill slits and
tails, shown in fig 4.21. However, the ‘gill slits’ are not gills; they connect the throat to the
outside, but in many species they close later in development. However, in fish and larval
amphibians they contribute to the development of gills.

Figure 4.22 Similarities in development of embryos

The embryonic tail does not develop into a tail in all species, but in humans, it is reduced
during development to the coccyx, or tailbone. The more similar the patterns of embryonic
development, the more closely related species are assumed to be. The similarity in the
pattern of development of the vertebrates suggests, again, a common ancestor.

How does comparative Biochemistry support the theory of evolution?

Biochemistry deals with biological compounds that the body is made up of. Various
chemicals have been studied in order to find evidence of evolutionary relationships. The
idea behind this is that if organisms share very similar molecules and biochemical
pathways, then they must be closely related evolutionarily. Chemicals that have been used
in such analysis include:
 DNA- the base sequences of DNA from different organisms is compared.
 Proteins such as Cytochrome C (found in the electron transport chain of respiration)
and Hemoglobin are compared in terms of amino acid sequences. Species that are closely
related have the most similar DNA and proteins. Those that are distantly related share fewer
similarities. Using DNA hybridization, 99.9% of chimpanzees DNA sequence are very
closer to humans.

DNA hybridization technique measures the extent to which a strand of DNA from one
species can bind with (or hybridize with) a strand of DNA from another species. In this
technique, the double Helix of the DNA molecule is heated to separate it into single strands
and then the single- stranded DNA (ss DNA) from both species is mixed and the mixture
cooled.

Although the ss DNA from species A and species B will hybridize (bind) as it cools, it will
not do so along all its length. There will be regions that are mismatched (the base pairs are
not complementary) and so do not bind and there are techniques available to measure the
percentage of this mismatching. The hemoglobin molecule is similar in all animals that
possess it, but there are differences. For example, the hemoglobin of the lamprey (a
primitive fish-like animal) has only one poly peptide chain, not four. Most animals have
hemoglobin with four chains, but the chains do vary.

Figure 4.23 The evolutionary relationships of some animals

shown by differences in haemoglobin
Figure 4.22 above shows the differences in the amino acid sequences of the ∝ chain of
human and several other animals. Difference in amino acid sequences of cytochrome C
gives a similar picture.

How does plant and animal breeding support the theory of Evolution?
Humans have been trying to improve the yields of their crop plants and stock animals for
thousand years using selective breeding, in which
 Those animals/ or plants/ that show the desired trait are selected and mated, and
E. g: High milk yield
Large number of seeds per pod
 The offspring are monitored carefully, and again only those with the desired trait are
allowed to breed
Over many generations, selective breeding can bring about significant changes to the
organisms involved. Example: the modification by selective breeding then natural selection
should also be able to produce new varieties, and eventually new species.

Figure 4.24 The wild bear has been selectively bred to produce
the domestic pig

What are the different types of natural selection?

The modern view of natural selection states that those members of species which are best
adapted to their environment will survive and reproduce in greater numbers than others less
well adapted. They will pass on their advantageous alleles to their offspring and, in
successive generations, the frequency of these alleles will increase in their gene pool. The
advantageous type will, therefore, increase in frequency in successive generations.

Natural selection is the ‘driving force’ behind evolution. It is the process that brings about
changes (over time) in populations that can, eventually lead to different populations of the
same
species becoming different species. Natural selection eventually leads to speciation (the
formation of new species).

Species is defined as a group of similar organisms with a similar biochemistry, physiology

and evolutionary history that can interbreed to produce offspring that are fertile.

The different types of selection include

 Directional selection
 Stabilizing selection
 Disruptive selection

What is directional Selection?

 Directional selection operates in response to gradual changes in environmental
conditions. It favors one extreme phenotype from the population. In this way the
population genetic diversity is reduced and it leads to a shift in the population average
for the selected character over successive generations, one phenotype gradually replaces
another.

For example: - thicker fur (longer hair) in foxes is an advantage in cold climate. Thinner fur
in foxes is advantage in a hot climate.

Overtime, selection operates against the disadvantaged extreme and in favour of the other
extreme. The mean and range of values shift towards the favored extreme.

Figure 4.25 Directional selection

What is Stabilizing Selection?
In stable environment, individuals at both ends of the range of values for a feature are the
least well adapted. Selection often operates against both these extremes to reduce the
variability in the population and to make the population more uniformly adapted.

Figure 4.26 Stabilizing selection

What is disruptive Selection?

Disruptive selection is, in effect, the converse of stabilizing selection. In this instance,
individuals at both extremes of a range have some advantage over those displaying the
mean value. As a result, the frequency of those individuals at the extremes of the range will
increase over time and those in the middle of the range will decrease over time. This is the
part of explanation of the evolution of Darwin’s finches.

Figure 4.27 Disruptive selection

How can natural Selection lead to the formation of New Species?
Natural selection provides a mechanism by which new populations of a species can arise.
But at what point can these populations be considered as distinct species? Species are a
group of similar, interbreeding organisms that produce fertile offspring. There are a number
of ways in which individuals from different population cannot interbreed to produce fertile
offspring. The two main ways are:

 Allopatric speciation, and

 Sympatric speciation

Both allopatric and sympatric speciation involves isolating mechanisms that prevent
different populations from interbreeding for a period of time. The two population become
‘reproductively isolated’ and effectively become distinct species when mutations that arise
in one population cannot be passed to the other, different selection pressures in the different
environments, genetic differences between the two populations increases.

What is allopatric Speciation?

It is speciation caused by geographic isolating mechanism; the species become isolated by
some physical feature such as:

 A mountain range being created

 A land mass separating two bodies of water
 A river changing course

This is a type of geographical isolation. Interbreeding between the populations becomes

impossible and speciation could result. In this instance, two distinct species have evolved
from one original species as a result of geographical isolation and allopatric speciation.
Figure 4.28 Allopatric speciation in the shrimp population of the North Pacific Ocean and

the Caribbean Sea

What is Sympatric Speciation?

Speciation need not involve physical separation. The two diverging populations may inhabit
the same area, but be prevented from breeding in a number of ways, including
 Seasonal Isolation: members of the two populations reproduce at different times of the
year
 Temporal isolation: members of the two populations reproduce at different times of the
day.
 Behavioral isolation: members of the two populations have different courtship patterns.

What is polyploidy and why is it important in plant Evolution?

Diploid- chromosome in pairs- there are two sets of chromosomes in a cell
Haploid- chromosomes are single- there are one set of chromosomes in a cell.
Polyploidy Cells - have many sets of chromosomes per cell- sometimes four sets, sometimes
eight or more some human liver cells have 92 chromosomes per cell-they are tetraploid -
they have four sets of chromosome per cell.

Polyploidy has been important in plant evolution because it has allowed otherwise infertile
hybrids to become fertile again. When different species form hybrids, very often the hybrids
cannot produce offspring because all the chromosomes cannot form bivalents (homologous
pairs) in meiosis. So they cannot form sex cells and cannot reproduce.
 Figure 4.29 Hybridization and polyploidy in the evolution of modern wheat

If the chromosome number were to double, then all chromosomes are able to form
homologous pairs. Meiosis and sex-cell formation can take place and the hybrid is now
fertile. Hybridization and polyploidy have been important in the evolution of modern
wheat from

wild grasses. Fig 4.28 shown above depicts how Hybrid B is infertile because each cell
contains one set of chromosome (7) that came from Aegilops squarrosa and one set of
chromosomes (14) that came from Triticum durum. Clearly, with 21 chromosomes per
cell, there are not enough chromosomes for them all to form homologous pairs- even if
they were homologous. But when the hybrid doubled its chromosome number, there
were two of each chromosome. Now homologous pairs can form in meiosis and the
hybrid is fertile.

Triticum vulgare is one form of modern wheat polyploidy in addition to restoring

fertility to infertile hybrids, often results in bigger plants with more and bigger seeds.
What are divergent evolution and convergent evolution?

What is Divergent Evolution?

Divergent evolution is another name for a process called adaptive radiation. In
divergent evolution, a basic type diverges along different lines because of different
selection pressures in different environments.

If different selection pressures are placed on populations of a particular species, a wide

variety of adaptive traits may result. If only one structure on the organism is considered
(such as a limb), these changes can either improve the original function of the structure,
or they can change it totally. Divergent evolution leads to the development of a new
species.

Figure 4.30 Diverging evolutions of finches on the Galapagos Islands

Examples of divergent evolution (adaptive radiation) include:

 The evolution of different species of finches on the Galapagos Islands.
 The evolution of the different forms of the pent dactyl limb.

What is Convergent Evolution?

Convergent evolution takes place when different organisms occupy similar niches. The
selection pressures on the populations are the same and so similar adaptations evolve
over
time. In convergent evolution, on the other hand, unrelated species become more and
more similar in appearance as they adapt to the same kind of environment.
Example: - the convergent evolution of the giant armadillo, giant pangolin, giant
anteater and spiny anteater.

Figure4.31 Convergent evolution in anteater

They are not related evolutionary, but all feed on ants and must obtain ant from narrow
cracks in the ground. The similarity between the four is the result of convergent
evolution. Convergent evolution is also responsible for the wings of a bird, a bat and the
extinct pterodactyl.

Who are we and where have we come from? A loose language used in describing human
evolution. We heard people saying we evolved from chimpanzees’ or we evolved from
monkeys or ‘we evolved from apes’. None of these statements are accurate.

There has been a ‘line of evolution’ for millions of years that has given rise to old world
monkeys, a new world monkeys, the great apes and the different species of humans that
have lived. But we are Homo sapiens and we are the latest of several humans to live on
the planet. We have two features in particular that distinguish us from other primates.
These are:
 A very large brain, and
 Bipedalism the ability to truly walk on just two legs

Figure 4.32 The evolutionary tree for modern primates

Even though there existed debate among biologist about which comes first and about
exactly how this evolutionary tree has given rise to the various groups, and disagree
over the details, they all agreed about the idea- a line of evolution that has branched to
give the different groups of primates (including apes and humans) that exist today and
have existed in the not
too distant past. Humans and chimpanzees both evolved from a common ancestor that
lived about 6 million years ago.

Fig 4.32 shows a timeline for the major hominin and hominid species according to
currently available fossil evidence. Fossils of many of the species along the early part of
the timeline were found in Ethiopia. It is indeed the ‘cradle of mankind’.
Figure 4.33 A timeline for the major hominin and hominid species

What is Significant about Lucy and Ardi?

Both Lucy and Ardi are important fossils in explaining the evolution of modern humans
and chimpanzees from a common ancestor.
Lucy: was discovered by Donad Johanson and Tom Gray in 1974 at Hadar in Ethiopia

 Is a fossil dated at about 3.2million years

 Was an adult female of about 25 years

 Belong to the species Australopithecus afarensis

 Here skeleton was about 40% completed, an unusually high proportion for a fossil
skeleton. Her pelvis, femur and tibia show that she was bipedal. There is, however, also
evidence that

Lucy was also partly arboreal (tree-dwelling). She was about 107cm (3’6’’) tall and
about 28Kg (62lbs) in weight. When she was discovered, Lucy represented one of the
oldest fossil hominis. The proportions of her humerus and femur were mid-way between
those modern humans and chimpanzees.

Figure 4.34 A- The original Lucy fossil; B- The Lucy display including the reconstructed
parts

Lucy had brain size about the same size as that of a chimpanzee, so her discovery was
able to settle a debate amongst biologists at the same time which came first, large brain
or bipedalism? Clearly bipedalism came before big brains.

The Ardi fossil (together with many other similar fossils) was first discovered in 1992,
in the Afar desert in Ethiopia, but it was only in 2009, after many year analysis, that
research paper published that gave Ardi a unique position in human evolution.

Ardi – was 1.2million years older than Lucy

 Was a female and belonged to the species Ardipithecus ramidus
 She was also bipedal
 4.4millin years old
 Is the nearest fossil to the ‘common ancestor’ of humans and chimpanzees

How has brain size Changed during Human Evolution?

During the course of human evolution, the brain has got bigger. When comparing
fossils, the cranial capacity increased with each new hominid species that evolved.
Besides becoming bigger overall, the brain has increased in size as a proportion of body
mass. Whereas species of Australopithecus have a brain that is between 0.7% and 1.0%
of their body mass, modern humans have a brain that is between 1.8% and 2.3% of their
body mass.

The brain of Homo sapiens uses 25% of the resting energy requirement, compared with
8% in the great apes. A large brain allows humans to:

 Run faster and in a more upright posture

 Plan in advance to avoid attack
 Develop and use tools and weapons

These abilities also depends on other physical adaptations such as

 Longer legs
 More nimble fingers, and
 A straighter spine

Are we still Evolving?

Homo sapiens (modern humans) first appeared in Africa and have since migrated to all
other parts of the world. Figure 4.34 shows migratory patterns together with the time.
 Figure 4.35 The migration of Humans out of Africa- it all begins near
Ethiopia. Number indicates the time (in years) since each stage of the
migration.

As humans moved from Africa into different areas of the world, they encountered
different environments. Different selection pressures in the different environments
resulted in the different human populations evolving along different lines.

For example, as humans encountered colder climates body features that gave a survival
advantage by helping to conserve heat were selected. These include:
 A shorter, squatter body shape
 These reduces the surface-area-to volume ratio and so reduces the rate of heat loss
by radiation
 An increased layer of adipose time under the skin to act as insulation.
 Increased hairiness; this reduces heat loss by convection

Humans have been evolving into different ‘races’ for thousands of years. There are three
main races with several subdivisions with difficult and disagreement on classification
bases of these races. Of course it is based on a recent genetic analysis of different races.

 African (Negroid), 100 million people from Africa and Melanesians of the south
pacific
 Eurasian (Caucasoid), 1000 million people with variable skin color ranging from
white to dark brown. Three subdivisions exit.
 Nordic- often tall, blonde and narrow-headed includes people from Scandinavian
and Baltic countries, Germany, France, and Britain.
 Mediterranean- usually lighter in body build, dark and narrow headed; includes
people from southern France, Spain, Italy, Wales, Egypt, Jews, Arabs, Afghanistan,
Pakistan, India.
 Alpine- usually broad-headed, square Jaws, olive skin, brown hair; includes people
from countries from Mediterranean to Asia.
 East Asia (Mongoloid), most numerous of the present-day populations and split into
three groups:

 Eastern Siberians, Eskimos and the Northern American Indians

 Japanese, Koreans and Chinese
 Indonesians and Malays
 A B C
Fig. 4.36 A - Example of African features; B - Example of Eurasian features; C -
Example of East Asian features

However, this classification does not include the central African pigmies, the Bushmen
and the Australoids. Some thousands of years ago the human populations or races might
have been beginning to evolve into separate species with certain physical and genetic
difference emerged between the different races. However, our large brain has intervened
into major ways:

 We developed the skill to design and manufacture all kinds of thinner from
buildings to tools to clothes. This effectively allowed us to become able to adapt to
it.

 We developed global travel. This has allowed humans of all races to interbreed,
throwing many of the genetic differences that have revolved into a huge human
melting pot.
5.1 AN INTRODUCTION TO BEHAVIOR

What is behavior?
Behavior can be defined in a number of ways, depending on our perspective, or view point.
Some definitions of behavior are listed below:
 The observable response a person make to any situation
 A manner of acting or conducting yourself
 The way a person behaves towards other people
 The actions or reactions of a person or animal in response to external or internal
stimuli
 The response or reactions or movements made by an organism in any situation.

However, from a biological view point, none of these is quite complete. Therefore, Behavior is
defined as co-ordinated response of an organism to an internal or external stimulus. It is
brought about because of sensory, neural and hormonal factors. Behavior includes activities
of organisms such as feeding, mating, courtship, nest building and communications. Ethology
is the study of behavior in its natural habitat. It involves investigating the relationship of
animals to their physical environment as well as to other organisms.

For an organism to show a co-ordinated response, then any behavior must have these
components
 A receptor of some kind to detect the stimulus
 An effector of some kind to produce the response and
 Some kind of linking system or co-ordinating system that is influenced by the
receptor and can influence the effector.

Stimulus Receptor
Co-ordinating system

Response Effector

Figure 5.1A generalized model of the components of behavior

How do plants respond to Unidirectional Stimuli?

 Tropisms are growth responses of plants. The growth movements are either toward the
direction of the stimulus (Positive tropism) or away from the direction of the stimulus (negative
tropism). If you put a plant on a windowsill, the plant shoots grow towards the window for the
intensity of light is greater on the window than the other side. Shoots grow toward light
stimulus, are positively phototropic but away from gravity, and are negatively phototropic.
This behavior is called phototropism.

Figure 5.2 Plant stems grow towards the area of greatest light intensity

The benefit in plant stems growing towards the greatest intensity of light is that stem
automatically direct their leaves for the chlorophyll and other pigments in the leaf cells can
absorb the maximum amount of light for photosynthesis.

This response is co-ordinated by plant growth substances called auxins which are produced in
the short tip in response to light and move downwards and away from light to the ‘dark’ side of
the shoot. The auxins stimulate the shoot cells to divide and enlarge so that growth is greatest
on the side away from light. As this side grows more, it causes the shoot to bend towards light.

Light from one side Receptor cells in the shoot tip

Auxins produced and move away from light

Cells on dark side of stem grow fastest

Shoot grows towards light
Figure 5.3 phototropism in plant shoots

The root grows more or less downwards because of the unidirectional stimulus called gravity.
The response of plants to this stimulus is called geotropism. Plant roots are positively
geotropic while plant shoots are negatively geotropic. This means that the roots will grow
towards an environment in which they can anchor the plant, absorb water and absorb mineral
ions.
How do Simple Animals respond to Stimuli?
There are two different types of responses in simple organisms. These are:
 Taxes (sing Taxis) – in which the animals moves along a gradient of intensity of a
stimulus towards the greatest intensity of the stimulus (a positive taxis) and
sometimes away from the greatest intensity (a negative taxis).
For example: a unicellular protoctistan Euglena swims (using its flagellum)
towards areas of increased light intensity. This is positive photo taxis and allows the
organism to photosynthesis efficiently.

 Kinesis (sing Kinesis), in which a change in the intensity of the stimulus brings
about a change in the rate of movement.
For example: woodlice increase their rate of movement in bright light. This
increases the probability that they will move into a dark area, where it is usually
more humid and they will lose less water.

How do woodlice respond to a change in the intensity of light?

Woodlice are small land-dwelling crustaceans. There are many different species, but are quite
similar. Because of their flattened shape and small size, they have a relatively large surface
area-to-volume ratio. This means that they tend to lose water quickly through body surface.
This happens because they have no waxy cuticle covering their bodies to limit loss of water.
They are typically found under logs, stones, bark and amongst leaf litter. These areas all have a
more humid atmosphere, which reduces the rate of water loss from the wood lice. When
brought into light, the woodlice start to move around much more quickly. This increased rate of
movement is a response to the increased intensity of light- it is a kinesis.

Detected by ocelli
(Simple eyes)
Nerve cells transmit impulses to/from central Nervous system

Increased movement Increased rate of muscle contraction

Figure 5.4The response of woodlice to Light

Why is it important to study behavior?

The study of animal behavior is often called ethology and the biologists who work in this field
are known as ethologists. Studying animal behavior has made many contributions to other
areas of science, in particular to the study of human behavior, but also including:
 Neuroscience
 The environment and resource management
 Animal welfare
 Science education
The Impact of the study of animal behavior on human society
Many problems in human society can be related to the interaction of environment and
behavior, or genetics and behavior. Social scientists turn to animal behavior as a basis for
interpreting human society and understanding possible causes of problems in society. Specific
example includes:
 Research by de Waal on chimpanzees and monkeys has illustrated the importance of co-
operation and reconciliation in social groups. This work has implications for aggressive
behavior among human beings.
 Harlow’s work on social development in rhesus monkeys has been of major importance
to theories of child development and attachment formation. Research in humans
triggered by this shows that feeding is not a major stimulus for attachment formation.

Figure 5.5 One of Harlow’s monkeys and its two ‘mothers’

 Basic research on circadian and other endogenous rhythms in animals has led on to
research relevant to humans in areas such as coping with jet-lag or shift-working.

The Impact of Study of animal behavior on Neuroscience

 Neuroethology: carefully collected behavioral data allows neurobiologists to focus their
studies on specific stimuli and specific response to determine neural pathways.
 Recent work in animal behavior has demonstrated the influence of behavior and social
organization on physiological and cellular processes. Variation in social environment
can inhibit or stimulate ovulation, induce miscarriages and so on.
 Other animal studies show that the quality of the social environment has a direct effect on
immune system functioning.
The Impact of the study of animal behavior on management of the environment and
resources
The behavior of animals often provides early clue of environmental damage. Change in sexual
and other behavior occurs much sooner and at lower levels of environmental disruption than
changes in population size.
Specific examples related to resource management include:
 Research on how salmon migrate back to their home streams has taught us much about
the mechanisms of migration. This has been valuable in preserving the salmon industry,
in the Pacific Northwest and has also helped in the development of a salmon fishing
industry in the great lakes of the USA.
 Knowledge of honeybees’ foraging behavior has given important information about
mechanisms of pollination, which in turn has been important for plant breeding and
propagation.

The Impact of the study of animal behavior on animal welfare

Animal behavior researchers look at the behavior and well-being of animals in the Lab and in
their natural environment. Such research has ensured reasonable and effective standards for
the care and well-being of research animals. Improved conditions for farm animals, breeding
of endangered species and proper care of companions’ animals all require information about
behavior patterns.

The impact of study of animal behavior on science education

Courses at universities in animal behavior and behavioral ecology often interest students in
behavioral biology so that partly boosts the interest for science.

5.2 INNATE BEHAVIOUR

What is innate behavior?

Innate behavior is a behavior that is present (potentially) at birth or hatching. It is also

described as patterns of inherited, pre-set behavioral responses, which develop along with
developing nervous system. It does not have to be learned.
Example: - The young herring gull ‘knows’ that if it pecks the orange spot on the beak of the
adult gull, it will receive food.
Characteristics of innate behavior
 It is performed in a reasonably complete form the first time it is shown under normal
condition.
 It is programmed by the genes.
 There is no learning or past experience needed.
 It is stereotypical for the species (all organisms of the same species perform the same
innate behavior the same way: there is no individuality), but may be developed,
modified and subjected to selection over many generations.
 It is behavior that is built in(inborn).
 It is common to all members of a species.
  It is fully functional the first time they are performed.

Figure 5.6 Innate behaviors in herring gulls

Types of Innate Behavior

There are three types of innate behavior
1. Reflex actions
Reflexes are often considered to be one of the simplest forms of behavior in which a single
action is performed in response to a specific stimulus. Responses over which we have no
control are known as reflexes. Reflexes are immediate, involuntary responses which are
not under the conscious control of the brain. Reflexes are necessary for organisms to
survive because they are always being protective.
Examples: -Blinking, sneezing, kneejerk, coughing, and withdrawal of your hand away
from a hot object.
2. Orientational
Orientational behaviors such as kinesis and taxes of woodlice and other simple
animals are more complex behaviors result in the organism behaving to move away
from unfavorable conditions and remain in favorable conditions.
3. Instinctive behavior
Often involve the most complex behavior but there is always a fixed action pattern for
each key stimulus. Once begun, the fixed action pattern is carried out to completion,
even if other stimuli intervene. The graylag goose always retrieves an egg that has been
bumped out of her nest in the same manner. This is a fixed action pattern (FAP). She
carries this sequence to completion, even if the egg slips away during the process.
 Figure 5.7 Fixed action patterns in graylag goose

Example: - Migratory behavior of some birds and locusts, spinning of a web by spider and the
way the honeybees share out all the work in the hive.
Examples of innate behavior include:
 The withdrawal of our hand from a hot object (reflex)
 Blinking when some dust gets in our eye (reflex)
 The kineses of woodlice in response to changes in light intensity and humidity
(orinetational)
 Nest-building (instinctive)
 Imprinting (instinctive)
 Weaving a web (instinctive)
How are Reflex actions brought about?
There are two main kinds of reflex actions:
A. Those that involve our special senses (eyes, ears, pressure detectors, etc.) and produce
a response by muscle, called Somatic Reflexes. These include the ‘knee-jerk reflex’ and
the ‘withdrawal from heat’ reflex many of these reflexes are protective.
B. Those that involve sensors in internal organs and produce responses also in internal
organs, called Automatic reflexes. These include the reflex actions controlling heart
rate and breathing rate.
One has to look at the structure of the nervous system to understand how these two types of
reflex action operate. Our nervous system is divided physically into two major components:
1. The central nervous system (CNS) - Comprises brain and spinal cord, and
2. The peripheral nervous system (PNS) - Comprising the cranial and spinal nerves each
containing many sensory and motor neurons.

Figure 5.8The components of nervous system

Our nervous system is also divided functionally into:

A. The somatic nervous system (SNS), which integrates information from the special senses
to produce responses in skeletal muscle, and
B. The autonomic nervous system (ANS), which integrates information from receptors in
internal organs and produces responses in the same or other organs or glands.

The autonomic nervous system is further divided into:

 The sensory division - transmits sensory nerve impulses into the central nervous system
 The sympathetic division - transmits impulses from the central nervous system to the
organs, generally preparing the body for ‘flight or fight’.
For example: -Increase cardiac output and pulmonary ventilation

  The parasympathetic division - acts antagonistically to the sympathetic branch and
prepares the body for ‘rest and repair’, decreasing cardiac output and pulmonary
ventilation.

What are Biological Clocks?

The term ‘biological clock’ is used to describe some internal regulatory mechanism that
controls various cyclical responses in living things. Both plants and animals show yearly,
monthly, daily and other cyclical changes that are genetically programmed.
Since biological clocks are present in so many different types of organisms, biologists believe
that they have evolved independently in these groups and are an example of convergent
evolution.
Daily rhythms are called circadian rhythms (from Latin words ‘circa’, meaning about, and
‘dies’, meaning a day). Circadian clocks have two main features:

 They will persist with a period of about 24-hours in the absence of environmental cues.
 They can synchronies to a 24 hour cue, such as the light-dark cycle; this is called
entrainment.

The biological clock of mammals and of some other animals is found in a small area of the
hypothalamus of the brain, called the suprachiasmatic nucleus. This sends impulses to a gland
called the pineal gland, which secretes a hormone called melatonin during the night, which
promotes sleepfulness and so controls the sleep-wake cycle. Because of this if we did not have
other cues to wake us and send us to sleep; we might expect to have a different sleep-wake
cycle in the summer compared to the winter.

Figure 5.8 The location of the supra-chiasmatic nucleus

In a study of 26 people maintained in a constant environments for six days in summer and six
days in winter, the result shown in table 5.1 were obtained.

Clearly the shorter nights of summer have an effect but not quite what one would expect. The
subjects woke earlier in summer, but also went to bed earlier. However, the shorter nights did
result in a reduction of 21 minutes of sleep.

Many other animals show circannual (Yearly) rhythms in behaviors such as

 Migration (E.g. swallows)
 Hibernation (E.g. hedgehogs)
 Coat growth (E.g. arctic foxes)
 Camouflage coloring (E.g. arctic foxes)

Figure 5.9 Examples of circannual rhythms. A) Hibernation B) Migration

What is instinctive behavior?

Instinctive behaviours are pre-programmed patterns of behavior. They are not single actions
in response to a simple change in the environment like reflex actions. Instinctive behavior often
involves a
complex sequence of actions. Example: - the spinning of a web by spiders Characteristic of
instinctive behavior:
 It is common to all members of a species
 It is fully functional the first time they are preformed (they require no learning)
 There is a key stimulus that triggers the behavior
 There is an innate releasing mechanism that links the stimulus to the response (this
may be nervous or hormonal).
 There is a fixed action pattern in response to the key stimulus that is always the same,
and
 Instinctive behavior are adaptive they have been retained in the species by natural
selection because they confer a survival advantage.

The feeding behavior of herring gulls is an example of instinctive behavior. The orange spot on
the beak is the key stimulus and pecking is the fixed action pattern. This is not much more
complex than some reflex actions. However, aggression in sticklebacks (fish) involved more
complex responses.

Male sticklebacks are very territorial; they will attack any other male that invades their
territory. The ethologist Niko Tinbergen, in some famous experiments, was able to show that
the key stimulus was the red belly of the entering male. The defending male attacked any non-
fish model that had red on its ventral (lower) surface.

Figure 5.10The models used by Niko Tinbergen

However, it turns out that the red belly-the key stimulus- provokes a very different fixed action
pattern in female sticklebacks. They find it irresistible and it stimulates mating behavior.

In an investigation into nesting behavior in lovebirds, there is some evidence that some fixed
action patterns can be modified slightly by experience- two different species of love birds with
different nesting behavior were interbred.
Female Fischer’s lovebirds cut short strips of nesting material, which are carried individually
to the nest. Female peach-faced love birds cut short strips and carry several at a time by
tucking them into their back feathers.

Hybrid females from the crosses exhibited the following behavior. In the first mating season
they
 Cut intermediate length strips
 Tried, but failed, to transport them by tucking into back feathers
 Learned to carry strips in their beaks

Imprinting is another kind of instinctive behavior in which the fixed action pattern is for newly
born/ hatched organisms to imprint on (or become attached to) the first thing they see that has
certain general features (those of an adult of its species). Many species of birds like swans,
chickens, ducks and geese will follow the first moving object they see for two or three days after
hatching and will continue to show this following response as they mature. The phenomenon is
known as imprinting. Under natural circumstances, the first object they would normally see is
their mother. Imprinting is a simple and specialized sort of learning which only occurs in very
young animals.

In his most famous study, Konrad Lorenz divided the newly hatched goslings (a gosling is a
young goose) leaving some with the mother and the rest are kept with himself for a few hours.
The goslings started to follow Lorenz around as if he was their mother. From that day on, they
followed Lorenz and showed no recognition of their own mother or other adults of their own
species. The young reared by the mother showed normal behavior following their mother. This
early imprinting lingered into adulthood. The birds continued to prefer the company of Lorenz
and other humans to that of their own species and sometimes even tried to mate with humans.

However, if the goslings are not offered any object to follow within a couple of days after
hatching, they lose their readiness to imprint. This shows us that imprinting will only take place
during a sensitive period in their lives and will never be repeated later on. Thus it appears that
the young animals are primed during a short sensitive period early in their lives to form a
learned attachment to a moving object, normally their mother. Imprinting is a type of learned
behavior with a significant innate component acquired during a limited critical period. Critical
period is a limited time during which learning can occur, a feature that distinguishes
imprinting from other forms of learning. Lorenz considered that imprinting, unlike other forms
of learning is irreversible, is restricted to the brief sensitive period just after hatching.
 Figure 5.11 Imprinting. A) Konrad Lorenz and the geeze B)The young goosling and
their mother

5.3 LEARNED BEHAVIOR

What is learned behavior?

Learned or acquired behavior is not a behavior that we have inherited from our parents.
Learning is the alteration of behavior by experience and most learning experiences take place
gradually and through repeating. They also have long-term effects. Most biologists define
learning as the strengthening of existing responses of the formation of new response to existing
stimuli that occurs because of practice or repetition.

Unlike innate behavior, learned behavior patterns are rarely fully functional the first time they
are performed. At the very simplest level of learning, trial and error brings about an
improvement in the effectiveness of the behavior pattern.

Table 5.2 describes the main differences between innate behavior and learned behavior.
Innate behavior Learned behavior
 Genetically determined and common to all  The behavior is changed by, or develops through,
members of a species experience and may vary from individual to individual

 Behavior is fully functional at the first  The animal develops the behavior through trial and
attempt error or by insight
 Generally no modification of the behavior  The behavior may be modified by new experiences
 Adaptive behavior that has been retained as  Behavior is learned a new by each member of the
a result of natural selection species and may not be adaptive
 It is more important in lower organisms  It is more important in higher organisms

Characteristics of learned behavior

1. Learning is a process through which experience changes an individual’s behavior
2. Not all behavioral changes are due to learning
 3. Most learning experiences must be repeated. Although some types of learning do occur
after a single trial, most learning needs experience and this occurs gradually over
several trails. For example, see how a small child learning to walk. How many times
does he fall over before he is able to walk on his own.
4. The behavioral change that results from learning may not be expressed immediately.
For example, a person may memorize facts for a test, but the learning could only be
demonstrated when answering the exam.
5. Learning ability is the product of natural selection. We should not be surprised. In fact,
we should expect to see differences in the mechanisms and processes of learning
among species.

There are many different kinds of learned behavior, including:

 Habituation  associative learning
 Sensitization  classical conditioning
 Insight learning  latent learning

What is habituation?
Habituation is the simplest form of learning. It is a progressive loss of responsiveness to
repeated stimulation. Habituation is the fall or elimination of response to frequently occurring
stimuli that have no effect on the animal’s well-being. Habituation- is a process which results a
decreased response to a stimulus after repeated exposure to that stimulus over a period of time.
Example: - noticing a strong smell on entering a room, but some time later we don’t even
notice that there is any odor present- i.e. our sense of smell has demonstrated habituation
smelling has stopped responding to the odor even though it is still present.

Habituation can occur at different levels in the nervous system. It can happen because:
 Sensory systems may stop, after a while, sending signals to the brain in response to a
continuously present or often repeated stimulus; this is sensory habituation.
 The brain still perceives the stimulus is still present, but has simply decided no longer to
pay attention.
Example: - Prairie dogs –habituated to humans when located near their areas regularly while
they give alarm calls when large mammals, large birds or snakes approach them.

What is Sensitization?
Sensitization is an increase in response to a harmless stimulus when that stimulus occurs after
a harmful stimulus. It is learning to be hypersensitive to a stimulus. After encountering an
intense stimulus, such as an electric shock, an animal may often react vigorously to a mild
stimulus that it would previously ignored. For example touching the siphon of Aplysia gently
causes the animal to withdraw its gill-until it becomes habituated to the harmless stimulus.
However, if the gentle touch on the siphon is preceded by an electric shock (or other mildly
harmful stimulus) to the tail, then the gill withdrawal response is much stronger. The events in
one pathway of neurons (the painful stimulation of the tail) are clearly affecting the reflex arc
that controls the gill withdrawal reflex. The strength and duration of the sensitized response
depend on the extent of the initial sensitization.

In higher animals, peripheral sensitization refers to the sensitizations that result from changes
in neurons of the peripheral nervous system. Central sensitization refers to the same process
occurring in neurons of the central nervous system.

What is Classical Conditioning?

In classical conditioning a naturally occurring stimulus becomes associated with a different
stimulus, which also produces the same response. In the 19th century, the Russian physiologist
Ivan Pavlov discovered classical conditioning, a form of associative learning. He found that
dogs automatically salivate at the sight of food (unconditioned stimulus), a stimulus to which
the animal did not have to learn the response to it. If Pavlov always rang a bell, conditioned
stimulus, when he offered food, the dogs began slowly to associate this irrelevant (conditioned)
stimulus with food. Eventually the sound of the bell alone could cause salivation. It is called a
conditioned stimulus because the animal’s response becomes conditional upon its
presentation. This means that the behavior is conditional upon something happening. A
conditioned stimulus is a reflex that is not innate and needs to be learned by experience. An
unconditioned stimulus is an original reflex that is inborn and does not depend on experience.
The conditioned stimulus must always come first before the unconditioned stimulus. If the
conditioned stimulus is not followed by the unconditioned stimulus there will be a loss of
response. The loss of the response is called extinction. Classical conditioning has an adaptive
importance because it prepares the organism for future events. In this theory the various
stimuli and response are:

Figure 5.12The phases of classical conditioning

 The unconditioned stimulus (US)
This ‘unconditionally’, naturally and automatically triggers a response.
E.g. when we smell a favorite food, we immediately feel very hungry. The smell of the
food is the unconditioned stimulus.
 The unconditioned Response (UR)
The uncondioned response is the unlearned response that occurs naturally to the unconditioned
stimulus. E.g. Feeling hungry is the unconditioned response.
 The conditioned Stimulus (CS)
This neutral stimulus does not initially produce the unconditioned response. But, after
association with the unconditioned stimulus, it triggers the same response.

 The Conditioned Response (CR)

The conditioned response is the response to the previously neutral stimulus (which is the same
as the unconditioned response to the unconditioned stimulus).

Figure 5.13 Pavlov’s famous experiment on classical conditioning

Pavlov’s research involved the following phases:

 He fed the dogs at regular intervals to establish a routine; as he fed them, they salivated:
this is a natural conditioned response to the (natural) unconditioned stimulus of food.
 Then, as he fed them, he rang a bell; they continued to produce the same unconditioned
response (salivation) as the food was presented and the bell was rang. After a period, the
dogs salivated when the bell was rung without food being presented; this is now a
conditioned response to a conditioned stimulus.
What is Operant Conditioning?
Classical conditioning involves modifying an innate response by pairing it with a previously
neutral stimulus. Operant conditioning can modify more complex, voluntary behaviors by the
animal/ person learning to associate the behavior with certain specific consequences.
Operant conditioning is conditioning in which an animal forms an association between a
particular behavior and a result that reinforces the behavior. A reinforcer is a stimulus that
alters the probability of a behavior being repeated. Operant conditioning is the result of trial
and error. Thus operant conditioning is a form of learning that depends on trying out several
ways of doing things and then selecting the correct way. We learn how to drive a car as a result
of trial and error. If a new behavior produces beneficial results, the animal will continue to
modify its behavior in this way. If the behavior produces unpleasant results, the animal will not
repeat it.

When behavior has favorable consequences, the probability that the act will be repeated is
increased. This relationship may result because the animal learns to perform the behavior in
order to be rewarded. In this type of associative learning, the timing of events is very
important. The difference between classical conditioning and operant conditioning is that in
operant conditioning, the behavior must be spontaneously emitted. It is not initiated by a
stimulus as it is in classical conditioning. But the favorable result or reinforcement must follow
it closely.

When the reinforcer is withheld the response rate gradually declines. This happens in the same
way as the strength of the conditioned reflex decreases when the conditioned reflex was
presented many times without the unconditioned reflex. The process similarly is also called
extinction.
Reinforcement Increased

Behavior Consequence Likelihood of repetition

Figure 5.14Operant Conditioning

Punishment Decreased

The term ‘operant conditioning’ was first used by B.F. skinner, a behaviorist psychologist who
carried out a great deal of pioneering research in this area. Skinner identified three types of
responses that he called operant that can follow behavior.
 Neutral operant: response from the environment that neither increases nor decreases the
probability of a behavior being repeated.
 Reinforces: response from the environment that increase the probability of a behavior
being repeated, rainforcers can be either positive or negative.
 Punishers: response from the environment that decreases the likelihood of a behavior
being repeated.
Skinner carried out much of his research on rats and other animals using a box called Skinner
box.

Figure 5.14 A Skinner box

The Skinner box has various signal stimuli that include:

 Different colored lights
 A speaker to deliver a sound stimulus
 An electric grid in the floor to deliver a mild electric shock
There is also a lever that the animal can press which is linked to the delivery of pellets of food.
The animal can be conditioned in several ways, such as by:
 Simply learning that pressing the lever will result in food being delivered- the ‘pressing
action’ is reinforced by the reward of food.
 Only pressing the lever when either light is lit up, resulting in the reinforcement of food
being delivered.
 Only pressing the lever when one of the lights is lit; the other is linked to the electric
shock system. The ‘punishment’ of the shock on pressing this light results in the behavior
being diminished or extinct.

Animal trainers use a technique called shaping; which is based on operant conditioning, to
train animals to perform in specific ways. Specific examples where shaping is used include:
 Training guide dogs for the blind
 Training horses
 Training dolphins and killer Whales at marine parks
 Training zoo animals
What is latent learning?
Latent learning can be defined as the association of stimuli or situations without reward. The
essential difference between latent learning and trial and error learning (operant conditioning)
is the absence of reward in latent learning. There are situations in which animals learn without
any obvious reward. Animals explore new surroundings and learn information which may be
useful at a later stage. The word latent means something that is stored or hidden until it is
needed in the future. Much of experiments about latent learning were conducted on rats by
Edward Tolman, a behaviorist psychologist, in 1938.

Example: - One teacher drives another to school every day. Then, on one day, the ‘driver’ is
ill. The other teacher drives himself to school without getting lost. He learned the route to
school without reinforcement, but never had to use it until the usual driver was ill.

What is insight learning?

Insight learning is the highest form of learning and in many ways the most difficult to
interpret. It does not result from immediate trial and error learning but may be based on
information previously learned by other behavioral activities. Insight learning is based on
thought and reasoning. It involves associating the previous experiences with the present
conditions. It involves the ability to combine two or more isolated experiences to form a new
experience. Insight learning is mainly seen in the higher primates, particularly human beings.
Insight learning:
 Involves finding solutions to problems that are not based on actual experience (with trial
and error) but on ‘trials’ occurring mentally.
 Often the solution is learned suddenly, such as when a person has been trying to solve a
problem for a period of time and the solution appears almost ‘out of nowhere’.

Much of the pioneering research on insight learning was carried out by Wolfgang Kohler,
working with chimpanzees. For the experiments, the chimpanzees were placed in an enclosed
area. Kohler placed desirable ‘Lures’ such as fruit outside the enclosure and out of their reach.
He placed a variety of objects that could be used to obtain it inside the enclosure. The
chimpanzees had to work out a way of using one or more of the objects to obtain the ‘Lure’.

The chimpanzees learned to use boxes to obtain bananas placed on the top of enclosure. They
dragged them under the banana and climbed on them to reach the fruit. They became quite
accomplished builders, piling box on box to erect structures with a height of four boxes.
Figure 5.15 A chimpanzee assesses the problem Figure 5.16 Through ‘building’ the
chimpanzee achieves
his goal

5.4 EXAMPLES OF BEHAVIOR PATTERNS

What is courtship behavior?

Courtship behavior is an activity that precedes and results in mating and reproduction. It
allows members of a species to recognize each other and prevents or reduces attempts at
interbreeding between different species. Courtship interactions are complex, species specific
behaviors. Courtship typically includes a series of fixed action patterns and releasers ensuring
that the participating individuals are non-threatening, of the proper species, sex and
physiological condition for mating. It may also involve selection of a specific mate from a
number of potential candidates. Courtship may simply involve a few chemical, visual or
auditory stimuli, or it may be a complex series of acts by two or more individuals using several
methods of communications.

There are many different methods of communication that are used to attract a mate. These
include:
 The use of pheromones by some female insects to attract males from a distance
 The use of touch by painted turtles
 The courtship songs of frogs heard on spring nights in many different countries
 The songs of humpback whale under the sea, which can be heard hundreds of miles away.
In most animals, courtship behavior is innate and consists of a pre-programmed set of fixed
action patterns in response to a key stimulus. Despite being innate, the fixed action patterns are
often complex behaviors with the fixed action pattern in one animal (say the male) serving as
the stimulus for another
fixed action pattern in the other animal (the female). This interaction of fixed action patterns
continues until courtship is successful or until one of the pair tires.

Figure 5.17 Courtship behaviors in Zebra fish.

Figure 5.18 The role of each fixed action pattern in the courtship behavior
Fixed action patterns in courtship form an important part of the mating displays of birds.

Figure 5.19 The courtship behavior of a mallard drake

What is territorial behavior?

Most animal behavioral biologists would define territory as ‘Any space that an animal defends
against intruders of the same species’. Territorial behavior is found in nearly every species of
animal, even humans. Possessing territory gives the holder areas to forage for food and so
increases the chance of attracting a mate. It also reduces vulnerability to predators. Animals
that do not have a territory of their own may contest with the owner for a territory that is
already occupied. Such contests are called conspecific (same species) conflicts.

Territorial animals usually defend areas that contain one or more of:
 A nest
 A den, or mating site
 Sufficient food for themselves and their young

Males are usually the territorial sex, but in some species (such as fiddler crabs) females
maintain a territory also. When conspecific conflicts occur, they usually involve ritualistic
displays and rarely involve the animals actually fighting. Residents of a territory are difficult to
dislodge as they are often older and more experienced.

Defense threat displays may be visual as in the coloring of feathers or fur, auditory as in
birdsong or the howls of gibbons or olfactory through deposition of scent marks. Many
territorial mammals use scent marking (containing pheromones) to signal the boundaries of
their territories. The resident animal usually holds on to his (or her) territory only by
expending considerable time and effort in its defense. Sunbird, for example, can use up to
13000Kjoules per hour patrolling and defending their territory.
 Figure 5.20 Ethiopian wolves

The Ethiopian Wolf (Canis simensis) is also a social animal; the wolves live and hunt in packs.
They maintain a group territory by marking with urine (containing pheromones). All adult
animals (male and female) contribute to this marking behavior, particularly during patrols of
the territory. Some of the younger males occasionally mark but younger females never mark.

Defending a territory
Some animals defend their territory by fighting with those who try to invade it. Fighting uses up
a large amount of energy, and can result in injury or death. Marking a territory usually ‘warns
off’ intruders. Animals that do not mark territories use threats from one, or more, of
vocalizations, smell and visual displays.

Figure 5.21 A male robin threatening an intruder by using vocalizations and by exaggerating
its size.

The songs of birds and loud calls of monkeys are warning that carry for considerable
distances, and warn intruders that they are approaching someone else’s territory. If these
warnings are ignored, and the intruder enters the territory, or two animals meet near the
border of their adjacent territories, they usually threaten each other with visual displays. This
displays often either:
 Exaggerate an animal’s size by the fluffing up of feathers or fur or

 Show off the animal’s weapons.

Ritual Fighting is a behavior in which the acts of fighting are displayed, without any physical
contact.

Figure 5.22A younger male zebra challenges the older resident male

What is social behavior?

Social behavior is the set of interactions that occur between two or more individuals of the
same species that modify the behavior of individuals of the same species in a way that is usually
beneficial to the group as a whole. Social behavior serves many purposes and found in a wide
variety of animals, including some invertebrates, Fish, Birds, and Mammals.

Some of the benefits of social behavior are that it allows animals to:
 Form stable group (intra-specific aggression is reduced)
 Improve the effectiveness of reproduction
 Forage more efficiently- especially if source of food is localized
 Protect themselves against attack more effectively
 Increase the chance of surviving migration - some birds travel in large group-many geese
fly in a ‘V’ formation-to reduce total wind resistance-the lead rotates in position
 Communicate across long distances
 Increase the chance of surviving extreme conditions
 Figure 5.23 Penguins ‘huddling’ to reduce heat loss

Social behavior in bees

Honey bees and bumble bees and other species of insects exhibit what is called eusociality.
Eusociality has three main features:
 There is cooperation in caring for the offspring as a consequence many individuals are
caring for offspring that are not their own.
 There are usually several generations in the colony so that it will sustain for longer and
allow offspring to assist parents and,
 There is division of labor-not every individual in the group is reproductively active; in
the case of bees, the queen is the only.
There are three different types or castes of bees in a nest. They are
 The queen- the only truly reproductively active female (1st caste)
 Workers- non-reproductively active female (2nd caste)
Drones- reproductively active male (3rd caste)

Table 5.3A summary of the roles of different casts of bees.

The queen secretes powerful pheromones within the nest that control the behavior of the
workers at different stages of their development and so help to maintain the social structure of
the nest. She also makes aggressive attacks on maturing worker bees.

If the queen does not produce these pheromones, or if she produces too few eggs, then the
structure of the nest breaks down. She may be attacked by mature workers, one of whom will
replace her. A honeybee colony may last for several years, with the male drones being driven
out of the nest over winter to preserve resources for the workers and the queen more drones
will emerge the following spring.

At the of the colony cycle, the queen, the drones and most workers will die, leaving just a few
large workers, who will assume the status of queens and the following spring, fly away to
establish their own colonies.

Figure 5.24 The roles of worker bee at different stages of development

Worker bees communicate with each other in a very special way to convey information about a
source of nectar. Foragers perform a ‘wag-dance’ on the honeycomb to inform other workers
of the direction of the nectar source and its distance. The dance takes the form of a ‘figure of
eight’ on the vertical face of the honey comb.

Information about the nectar is conveyed in two ways:

 The angle of the dance away from the vertical corresponds with the angle of the nectar
from the sun
  The length of the ‘straight-run’ part of the dance is proportional to the distance from the
nest.

Figure 5.25 A and B show the orientation of the wag-dance on the honeycomb while C shows
the relationship of this dance to the position of the sun and the position of the nectar source.

Recent research shows that the foraging bees also use sound to inform other bees about the
distance of the source, and, perhaps, to help to ‘recruit’ these other workers. The time for
which they produce their sounds is directly correlated with the distance to the nectar source, as
figure 5.26 shows.

Figure 5.26 The length of sound production by foraging workers is proportional to the
distance to a food source.

The roles of the casts are the same in bumblebees and the queen maintains ‘order’ in the same
way. However, these nests are annual nests and a new colony establishes itself every spring.