Homo naledi: Difference between revisions

Homo naledi Temporal range: not dated
A sample of the 1,550 skeletal pieces recovered
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Primates
Family:	Hominidae
Genus:	Homo
Species:	†H. naledi
Binomial name
Homo naledi Berger et al., 2015
Location of discovery in Guateng, South Africa

Homo naledi is an extinct species of hominin, provisionally assigned to the genus Homo. Discovered in 2013 and described in 2015, fossil skeletons were found in South Africa's Gauteng province, in the Dinaledi Chamber of the Rising Star Cave system, part of the Cradle of Humankind World Heritage Site.^[1][2] As of 10 September 2015^[update], fossils of at least fifteen individuals, amounting to 1550 specimens, have been excavated from the cave.^[2]

The species is characterized by a body mass and stature similar to small-bodied human populations, a smaller endocranial volume similar to Australopithecus, and a skull shape similar to early Homo species. The skeletal anatomy combines primitive features known from australopithecines with features known from early hominids. The fossils have not yet been dated.^[3]

The fossils were discovered by recreational cavers Rick Hunter and Steven Tucker in 2013.^[2][4][5] Homo naledi was formally described in September 2015 by a 47-member international team of authors led by Lee Berger who proposed the bones represent a new Homo species. Other experts contend more analysis and evidence is needed to support this classification.

The word naledi means "star" in the Sotho language. It was chosen to correspond to the name of the Dinaledi chamber ("chamber of stars") of the Rising Star cave system where the fossils were found.^[1]

In October 2013 while exploring the Rising Star cave system, recreational cavers Rick Hunter and Steven Tucker of the Speleological Exploration Club of South Africa found a narrow, vertically oriented "chimney" or "chute" measuring 12 m (39 ft) long with an average width of 20 cm (7.9 in).^[2][4][5] Then Hunter discovered a room 30 m (98 ft) underground (Site U.W. 101, the Dinaledi Chamber), the surface of which was littered with fossil bones. Before they entered the cave that day the cavers knew that a scientist in Johannesburg was looking for fossils.^[2] When the Dinaledi Chamber was first entered, the sediments along the cave floor consisted largely of loosely packed, semi-moist, clay-rich clumps of varying sizes in which bone material was distributed. The bone material was distributed across the surface in almost every area of the chamber, including narrow side passages and offshoots, with the highest concentration of bone material encountered near the southwest end of the chamber, about 10–12 m downslope from the entry point, where the floor levels out.^[4][2] On 1 October 2013 photos were shown to geologist Pedro Boshoff, and then to Lee Berger.^[5][6]

In November 2013, the National Geographic Society and the University of the Witwatersrand funded an expedition called Rising Star Expedition for a twenty-one day excavation at the cave,^[7] followed by a second expedition in March 2014 with a 4-week excavation in the Dinaledi Chamber. In total, the expedition retrieved 1,550 pieces of bone belonging to at least fifteen individuals, found within clay-rich sediments.^[8][1] The layered distribution of the bones suggests that they had been deposited over a long time, perhaps centuries.^[2] Only one square meter of the cave chamber has been excavated; other remains might still be there.^[9][10][11]

Around 300 bone fragments were collected from the surface of the Dinaledi Chamber, and ∼1250 fossil specimens were recovered by excavation.^[4] The fossils include skulls, jaws, ribs, teeth, bones of an almost complete foot, of a hand, and of an inner ear. The bones of old, young and infants were found.^[2] Although much of the fossil material is disarticulated (separated at joints), the deposit contains articulated or near-articulated examples such as the maxilla and mandible of single individuals and the bones of the hands and feet.^[4]

The new species description was announced in a news conference and ceremony on 10 September 2015 in Johannesburg, South Africa.^[1][2][12] A display case of the fossils was unveiled during the ceremony.^[13]

The physical characteristics of H. naledi are described as having traits similar to the genus Australopithecus, mixed with traits more characteristic of the genus Homo, and traits not known in other hominin species.^[1]

Adult males stood around 150 cm (5 ft) tall and weighed around 45 kg (100 lb), while females were a little shorter and weighed a little less. These sizes fall within the range of small-bodied modern humans. An analysis of H. naledi's skeleton suggests it stood upright and was bipedal.^[14] Its hip mechanics, the flared shape of the pelvis are similar to australopithecines, but its legs, feet and ankles are more similar to the genus Homo.^[1][15]

The hands of H. naledi appear to have been better suited for object manipulation than those of australopithecines.^[1] Some of the bones resemble modern human bones, and other bones are more primitive than the australopithecine, an early ancestor of humans. The thumb, wrist and palm bones are modern-like while the fingers are curved, more australopithecine, and useful for climbing.^[2] The shoulders are configured largely like those of australopith. The vertebrae are most similar to Pleistocene members of the genus Homo, whereas the ribcage is wide distally like A. afarensis.^[1] The arm has an Australopithecus-similar shoulder and fingers and a Homo-similar wrist and palm.^[15] The structure of the upper body seems to have been more primitive than that of other members of the genus Homo, even apelike.^[2]

Four skulls were discovered, thought to be two females and two males, with a cranial volume of 560 cm³ (34 cu in) for the males and Template:Covert for females, approximately half the volume of modern human skulls; average Homo erectus skulls are 900 cm³ (55 cu in). The H. naledi skulls are closer in cranial volume to australopithecine skulls.^[2] Nonetheless, the cranial structure is described as more similar to those found in the genus Homo than to australopithecines, particularly in its slender features, and the presence of temporal and occipital bossing, and the fact that the skulls do not narrow in behind the eye-sockets.^[1] The species' brains were markedly smaller than modern Homo sapiens, measuring between 450 and 550 cm³ (27–34 cu in). The teeth and mandible musculature are much smaller than those of most australopithecines, which suggests a diet that did not require heavy mastication.^[1] The teeth are small, similar to modern humans, but the third molar is larger than the other molars, similar to australopithecines.^[15]

The overall anatomical structure of the species has prompted scientists to classify the species within the genus Homo, rather than within the genus Australopithecus. The H. naledi skeletons indicate that the origins of the genus Homo were complex and may be polyphyletic (hybrid), and that the species may have evolved separately in different parts of Africa.^[16]

A reconstruction of a model of a H. naledi head was made by measuring the bones of the head, the eye sockets, and where the jaw muscles insert to the skull. The measurements were used to make the model, including skin, eyes, and hair.^[17]

The fossils have not been dated as of 10 September 2015. The discovery team waited until after the research article was published before trying radiocarbon dating of the fossils because radiocarbon dating will have to destroy parts of the fossils.^[18][19][20] Radiocarbon dating can only date fossils which are 50,000 or fewer years old, and can determine if the fossils are younger than 50,000 years old.^[20]

The bones were found lying on the cave floor or buried in shallow sediment. Two fossil dating techniques—dating fossils within volcanic ash by dating the ash, and dating fossils within layers of calcite flowstone deposited by running water by dating the flowstone—cannot be used because the fossils were not buried in volcanic ash or in flowstone layers.^[2] For example: in East Africa, volcanic ash layers, which are datable, has helped to determine the age of fossils.^[2]

Berger said that the anatomy of H. naledi suggests it originated at or near the start of the Homo genus, around 2.5 million to 2.8 million years ago. The excavated bones may be younger.^[21] Tim White says that it is hard to know if the fossils are much less than one million years old or older.^[19]

Geologists estimate that the cave in which the fossils were discovered is no older than three million years.^[22]

The University of the Witwatersrand is the curator of the fossils.^[23] The fossils are owned by South Africa and will likely stay there, in accord with a 1998 resolution by the International Association for the Study of Human Paleontology – approved also by a South African permanent council member of the organisation–^[24] "strongly recommending that original hominid fossils not be transported beyond the boundaries of the country of origin, unless there are compelling scientific reasons which must include the demonstration that the proposed investigations cannot proceed in the forseeable future in the country of origin".^[23]

• The research team proposes the bones represent a new species, naledi in the genus Homo, other experts contend further analysis is needed to support this classification.^[9][18]
• Paleoanthropologist Tim D. White said the significance of this discovery is unknown until dating has been completed and additional anatomical comparison with previously known fossils has been done.^[19]
• Rick Potts said that without an age there is no way to judge the evolutionary significance of this find.^[21] He stated that "it's hard to know without a date whether it's from that period, as one of those experiments that then went nowhere, or whether it's in fact much less than one million years old. In that case, we could be talking about something that also didn't go anywhere and was just an isolated, probably very small population that persisted for a long time in splendid isolation."^[19]
• New York University anthropologist Susan Anton stated that even after dating, experts will likely spend many years striving to put these fossils in the proper context because there is no consensus in paleoanthropology about exactly how such comparisons are used to define the genus Homo. "Some would argue that striding bipedalism is a defining feature, so that being Homo means using a specific way of moving around the environment. Other scholars may look more to cranial characteristics as Homo family features."^[19]
• Bernard Wood, paleoanthropologist (George Washington University), agrees the remains represent a new species, but thinks the bones may represent a relic population that may have evolved in near isolation in South Africa, similar to another relic population, a small-brained species of Homo floresiensis from the island of Flores in Indonesia.^[15]
• With the number of individuals, and the sexes and age groups represented, scientists consider the find to be the richest assemblage of associated fossil hominins ever discovered in Africa,^[15] and aside from the Sima de los Huesos collection and later Neanderthal and modern human samples, it (the excavation site) has the most comprehensive representation of skeletal elements across the lifespan, and from multiple individuals, in the hominin fossil record.^[1][6]
• Jeffrey H. Schwartz, an evolutionary biologist at the University of Pittsburgh in Pennsylvania, argues that the material is too varied to represent a single species.^[25]

• Tim D. White stated that based on the published descriptions, the fossils belong to a primitive Homo erectus.^[19]
• Anthropologist Chris Stringer stated that the material looks most similar to the small-bodied examples of Homo erectus from Dmanisi in Georgia, which have been dated at ∼1.8 million years old".^[16]
• Berger rejected the possibility of the fossils representing H. erectus at the announcement news conference.^[21]

There are some indications the individuals were deliberately placed in the cave near the time of their death. some experts state more evidence is needed to support this hypothesis.

• Anthropologist John D. Hawks, from the University of Wisconsin-Madison who was a member of the team, stated that the scientific facts are that all the bones recovered are hominid, except for those of one owl; there are no signs of predation, and there is no predator that accumulates only hominids this way; the bones did not accumulate there all at once. There is no evidence of rocks or sediment having dropped into the cave from any opening in the surface; no evidence of water flowing into the cave carrying the bones into the cave.^[26] Hawks concluded that the best hypothesis is that the bodies were deliberately placed in the cave after death, by other members of the species.^[27]
• Dirks et al. say that "Mono-specific assemblages have been described from Tertiary and Mesozoic vertebrate fossil sites (...), linked to catastrophic events (...) Among deposits of non H. sapiens hominins, where evidence of catastrophic events is lacking, mono-specific assemblages have been associated typically with deliberate cultural deposition or burial". They stated that there is no evidence a catastrophe placed the bodies in the cave, and that the bodies were deliberately placed in cave.^[4]
• William Jungers, chair of anatomical sciences at Stony Brook University, does not dispute that the H. naledi bones belong in the genus Homo and were likely deposited deliberately, but he cautions against trying to argue for "complex social organization and symbolic behaviors." He suggests that "Dumping conspecifics down a hole may be better than letting them decay around you." He speculates that there may have been another, easier, way to access the chamber where the bones were found.^[7]
• Carol Ward, professor of pathology and anatomical sciences (University of Missouri) and not directly involved in the study, is also skeptical of the intentional burial explanation and asked, "If it’s really that hard to get to the cave, how do you get to that long dark cave carrying your dead grandmother?"^[28]

• Berger et al. speculate that "these individuals were capable of ritual behaviour". They speculate the placing of dead bodies in the cave was a ritualistic behaviour, a sign of symbolic thought.^[29] "Ritual" here means an intentional and repeated practice (disposing of dead bodies in the cave), and not implying any type of religious ritual.^[22] Ritualistic behavior has been generally considered to have emerged among Homo sapiens and Homo neanderthalensis.^[2] The oldest confirmed Neanderthal burial is 100,000 years ago.^[26]
• Potts describes it as more of a mystery: "There is no evidence of material culture, like tools, or any evidence any kind of symbolic ritual that we almost always associated with burial," he says. "These bodies seem to have simply been dropped down a hole and disposed of, and that really brings up a whodunit".^[19]
• Research article Dirks et al. (2015) states that "Every previously known case of cultural deposition has been attributed to species of the genus Homo with cranial capacities (brain size) near the modern human range. Unlike the Dinaledi assemblage, each of these hominin associated occurrences also contains at least some medium- to large-sized, non-hominin fauna".^[4]
• William Jungers is more dismissive of Berger's suggestion that H. sapiens may have inherited the practice of burying their dead from H. naledi, a creature with a much smaller brain than modern humans.^[7]
• Berger thinks that deliberate disposal of bodies within the intricate cave system would have required the species members to find their way through total darkness and back again, and he speculates that this would have required light in the form of torches or fires lit at intervals.^[2][30]

A PBS NOVA National Geographic documentary Dawn of Humanity, describing the discovery of H. naledi, was posted online on 10 September 2015, and broadcast nationwide in the United States on 16 September 2015.^[31] According to archeologist K. Kris Hirst, the Dawn of Humanity documentary film provides "a rich context for the discovery [of the fossils of Homo naledi], setting the historical and evolutionary background so that viewers can understand the significance of the discovery."^[32]

The National Geographic Society has videos on its website describing, explaining and showing different phases of the discovery, the scientists, the six women researchers, excavation of the fossils during a two-year period, and the process of making a model of a head of H. naledi from the fossils.^[33][34]

Fossil hand (palm and dorsum) of H. naledi

Fossil skull of H. naledi

Fossil foot of H. naledi – dorsal (A); medial (B); (C) arch – Scale = 10 cm (3.9 in)

Wikimedia Commons has media related to Homo naledi.

• Hominid species
• Prominent Hominid Fossils
• Exploring the Hominid Fossil Record
  Center for the Advanced Study of Hominid Paleobiology at George Washington University
• National Geographic blog of Rising Star Expedition members:
• Video (000:30) – Dawn of Humanity (trailer) on YouTube
• Video (113:07) – Dawn of Humanity (complete) (PBS WebSite)
• Three-dimensional scans of Homo naledi fossils at MorphoSource