Transactions of the Royal Society of South Africa, 2017
The hand metrics of Palaeolithic artists show a number of distinctive features that contrast with... more The hand metrics of Palaeolithic artists show a number of distinctive features that contrast with the low-variance hand metrics of modern Europeans, and with the majority of other modern humans. For example, the D2/D4 ratio in the Palaeolithic artists has a much greater spread of values and a greater degree of sexual dimorphism. We find that living San people, who represent the minority of modern humans that have high-variance genetics, also have a hand metric phenotype like the Palaeolithic artists, different from modern Europeans and other low-variance genetics modern humans. The increased variance and sexual dimorphism of the phenotypic D2/D4 ratio in the San measurements are in keeping with genetic evidence that the San represent one of the oldest human lineages with the greatest genetic diversity. The findings have the implication that the European Palaeolithic cave artists may have been derived from San-like migrants who brought an established artistic tradition from Africa to Europe, only to be replaced as a population, leaving no evidence of their genetics in modern Europeans, as observed for other Palaeolithic genes such as Oase 1.
The echidna, Tachyglossus aculeatus, a monotreme mammal, is thought to possess an all-rod retina ... more The echidna, Tachyglossus aculeatus, a monotreme mammal, is thought to possess an all-rod retina (O'Day, 1952). This study provides anatomical evidence for the presence of cone-like photoreceptors in the retina of the echidna. The cones, which constitute 10-15% of the photoreceptors, have all of the ultrastructural characteristics previously shown in the cones of placental mammals, and, like cones of other animals (Blanks & Johnson, 1984), they bind peanut agglutinin. Unlike the cones of another monotreme, the platypus, the cones of the echidna retina do not possess oil droplets. Twin cones, pairs of cones in which there is no obvious difference in the size, shape, or ultrastructural features of the members of a pair, are common. The density of cones varies from 9000 cells/mm2 in the superior periphery to 22,000 cells/mm2 in the central retina. Nearest-neighbor analysis suggests that the cone mosaic in the echidna retina results from the presence of single and twin cones in a re...
The primary structures of the hemoglobins of two Flying Foxes of the genus Pteropus are presented... more The primary structures of the hemoglobins of two Flying Foxes of the genus Pteropus are presented. Both comprise two components: in P. alecto hemoglobin two alpha-chains at a ratio of 1:1 and two beta-chains at a ratio of 4:1 were detected. The hemoglobin of P. poliocephalus comprises one alpha-chain and two beta-chains, the latter at a ratio of 1:1. The globin chains were separated by high-performance liquid chromatography and the sequences determined by automatic liquid and gas phase Edman degradation of the chains and their tryptic peptides. Compared with human hemoglobin, the alpha-chains of P. alecto and P. poliocephalus show 18 and 19 exchanges, respectively, whereas in the beta-chains 16/17 substitutions are found in both cases. In the alpha-chains of P. alecto, one exchange involves an alpha 1/beta 1-contact. In the beta-chains of both species one heme-, one alpha 1/beta 2- and two alpha 1/beta 1-contacts are exchanged. The relevant side chains are the same in both species. The functional and systematic aspects of these findings are discussed.
The primary structures of the alpha- and beta-chains of the single hemoglobin component from the ... more The primary structures of the alpha- and beta-chains of the single hemoglobin component from the tomb bat (Taphozous georgianus, Microchiroptera) are presented. After chain separation by reversed-phase HPLC the sequences could be determined by automatic gas and liquid phase Edman degradation of the chains and their tryptic peptides. The alpha- and beta-chains differ from human hemoglobin by 14 and 18 replacements, respectively. Compared to the total number of amino-acid exchanges, the exchange rate in the interhelical regions of the alpha-chains is surprisingly high (25%). It seems unlikely that substitutions at contact positions affect the oxygen binding properties of the hemoglobin.
The visual response properties of single neurons in the owl's visual Wulst suggest that t... more The visual response properties of single neurons in the owl's visual Wulst suggest that this forebrain structure is an analog of the mammalian visual cortex. Features in common with the cat and the monkey visual cortex include a precise topographic organization, a high degree of binocular interaction, and selectivity for orientation, direction of movement, and binocular disparity of straight-line contours.
Motion-induced blindness (MIB) is a phenomenon, perhaps related to perceptual rivalry, where stat... more Motion-induced blindness (MIB) is a phenomenon, perhaps related to perceptual rivalry, where stationary targets disappear and reappear in a cyclic mode when viewed against a background (mask) of coherent, apparent 3-D motion. Since MIB has recently been shown to share similar temporal properties with binocular rivalry, we probed the appearance-disappearance cycle of MIB using unilateral, single-pulse transcranial magnetic stimulation (TMS)--a manipulation that has previously been shown to influence binocular rivalry. Effects were seen for both hemispheres when the timing of TMS was determined prospectively on the basis of a given subject's appearance-disappearance cycle, so that it occurred on average around 300 ms before the time of perceptual switch. Magnetic stimulation of either hemisphere shortened the time to switch from appearance to disappearance and vice versa. However, TMS of left posterior parietal cortex more selectively shortened the disappearance time of the targets if delivered in phase with the disappearance cycle, but lengthened it if TMS was delivered in the appearance phase after the perceptual switch. Opposite effects were seen in the right hemisphere, although less marked than the left-hemisphere effects. As well as sharing temporal characteristics with binocular rivalry, MIB therefore seems to share a similar underlying mechanism of interhemispheric modulation. Interhemispheric switching may thus provide a common temporal framework for uniting the diverse, multilevel phenomena of perceptual rivalry.
Abstract As fundamental researchers in the neuroethology of efference copy, we were stimulated by... more Abstract As fundamental researchers in the neuroethology of efference copy, we were stimulated by Grush's bold and original synthesis. In the following critique, we draw attention to ways in which it might be tested in the future, we point out an avoidable conceptual error concerning emulation that Grush seems to share with other workers in the field, and we raise questions about the neural correlates of Grush's schemata that might be probed by neurophysiologists.
ABSTRACT Background: Interpreting the symbols found in the rock art of an extinct culture is hamp... more ABSTRACT Background: Interpreting the symbols found in the rock art of an extinct culture is hampered by the fact that such symbols are culturally determined. How does one break the circularity inherent in the fact that the knowledge of both the symbols and the culture comes from the same source? In this study, the circularity is broken for the Bradshaw rock art of the Kimberley by seeking anchors from outside the culture.Methods: Bradshaw rock art in the Kimberley region of Australia and Sandawe rock art in the Kolo region of Eastern Tanzania were surveyed in six visits on foot, by vehicle, by helicopter and from published or shared images, as well as from the published and online images of Khoisan rock art.Results: Uniquely shared images between Bradshaw and Sandawe art, such as the ‘mushroom head’ symbol of psilocybin use, link the two cultures and indicate that they were shamanistic. Therefore, many mysterious features in the art can be understood in terms of trance visualisations. A number of other features uniquely link Bradshaw and Sandawe cultures, such as a special affinity for small mammals. There are also many references to baobabs in early Bradshaw art but not later. This can be explained in the context of the Toba super‐volcano, the likely human transport of baobabs to the Kimberley and the extraordinary utility of the baobab.Conclusion: Many more mysterious symbols in Bradshaw rock art might await interpretation using the approaches adopted here.
Transactions of the Royal Society of South Africa, 2017
The hand metrics of Palaeolithic artists show a number of distinctive features that contrast with... more The hand metrics of Palaeolithic artists show a number of distinctive features that contrast with the low-variance hand metrics of modern Europeans, and with the majority of other modern humans. For example, the D2/D4 ratio in the Palaeolithic artists has a much greater spread of values and a greater degree of sexual dimorphism. We find that living San people, who represent the minority of modern humans that have high-variance genetics, also have a hand metric phenotype like the Palaeolithic artists, different from modern Europeans and other low-variance genetics modern humans. The increased variance and sexual dimorphism of the phenotypic D2/D4 ratio in the San measurements are in keeping with genetic evidence that the San represent one of the oldest human lineages with the greatest genetic diversity. The findings have the implication that the European Palaeolithic cave artists may have been derived from San-like migrants who brought an established artistic tradition from Africa to Europe, only to be replaced as a population, leaving no evidence of their genetics in modern Europeans, as observed for other Palaeolithic genes such as Oase 1.
The echidna, Tachyglossus aculeatus, a monotreme mammal, is thought to possess an all-rod retina ... more The echidna, Tachyglossus aculeatus, a monotreme mammal, is thought to possess an all-rod retina (O'Day, 1952). This study provides anatomical evidence for the presence of cone-like photoreceptors in the retina of the echidna. The cones, which constitute 10-15% of the photoreceptors, have all of the ultrastructural characteristics previously shown in the cones of placental mammals, and, like cones of other animals (Blanks & Johnson, 1984), they bind peanut agglutinin. Unlike the cones of another monotreme, the platypus, the cones of the echidna retina do not possess oil droplets. Twin cones, pairs of cones in which there is no obvious difference in the size, shape, or ultrastructural features of the members of a pair, are common. The density of cones varies from 9000 cells/mm2 in the superior periphery to 22,000 cells/mm2 in the central retina. Nearest-neighbor analysis suggests that the cone mosaic in the echidna retina results from the presence of single and twin cones in a re...
The primary structures of the hemoglobins of two Flying Foxes of the genus Pteropus are presented... more The primary structures of the hemoglobins of two Flying Foxes of the genus Pteropus are presented. Both comprise two components: in P. alecto hemoglobin two alpha-chains at a ratio of 1:1 and two beta-chains at a ratio of 4:1 were detected. The hemoglobin of P. poliocephalus comprises one alpha-chain and two beta-chains, the latter at a ratio of 1:1. The globin chains were separated by high-performance liquid chromatography and the sequences determined by automatic liquid and gas phase Edman degradation of the chains and their tryptic peptides. Compared with human hemoglobin, the alpha-chains of P. alecto and P. poliocephalus show 18 and 19 exchanges, respectively, whereas in the beta-chains 16/17 substitutions are found in both cases. In the alpha-chains of P. alecto, one exchange involves an alpha 1/beta 1-contact. In the beta-chains of both species one heme-, one alpha 1/beta 2- and two alpha 1/beta 1-contacts are exchanged. The relevant side chains are the same in both species. The functional and systematic aspects of these findings are discussed.
The primary structures of the alpha- and beta-chains of the single hemoglobin component from the ... more The primary structures of the alpha- and beta-chains of the single hemoglobin component from the tomb bat (Taphozous georgianus, Microchiroptera) are presented. After chain separation by reversed-phase HPLC the sequences could be determined by automatic gas and liquid phase Edman degradation of the chains and their tryptic peptides. The alpha- and beta-chains differ from human hemoglobin by 14 and 18 replacements, respectively. Compared to the total number of amino-acid exchanges, the exchange rate in the interhelical regions of the alpha-chains is surprisingly high (25%). It seems unlikely that substitutions at contact positions affect the oxygen binding properties of the hemoglobin.
The visual response properties of single neurons in the owl's visual Wulst suggest that t... more The visual response properties of single neurons in the owl's visual Wulst suggest that this forebrain structure is an analog of the mammalian visual cortex. Features in common with the cat and the monkey visual cortex include a precise topographic organization, a high degree of binocular interaction, and selectivity for orientation, direction of movement, and binocular disparity of straight-line contours.
Motion-induced blindness (MIB) is a phenomenon, perhaps related to perceptual rivalry, where stat... more Motion-induced blindness (MIB) is a phenomenon, perhaps related to perceptual rivalry, where stationary targets disappear and reappear in a cyclic mode when viewed against a background (mask) of coherent, apparent 3-D motion. Since MIB has recently been shown to share similar temporal properties with binocular rivalry, we probed the appearance-disappearance cycle of MIB using unilateral, single-pulse transcranial magnetic stimulation (TMS)--a manipulation that has previously been shown to influence binocular rivalry. Effects were seen for both hemispheres when the timing of TMS was determined prospectively on the basis of a given subject's appearance-disappearance cycle, so that it occurred on average around 300 ms before the time of perceptual switch. Magnetic stimulation of either hemisphere shortened the time to switch from appearance to disappearance and vice versa. However, TMS of left posterior parietal cortex more selectively shortened the disappearance time of the targets if delivered in phase with the disappearance cycle, but lengthened it if TMS was delivered in the appearance phase after the perceptual switch. Opposite effects were seen in the right hemisphere, although less marked than the left-hemisphere effects. As well as sharing temporal characteristics with binocular rivalry, MIB therefore seems to share a similar underlying mechanism of interhemispheric modulation. Interhemispheric switching may thus provide a common temporal framework for uniting the diverse, multilevel phenomena of perceptual rivalry.
Abstract As fundamental researchers in the neuroethology of efference copy, we were stimulated by... more Abstract As fundamental researchers in the neuroethology of efference copy, we were stimulated by Grush's bold and original synthesis. In the following critique, we draw attention to ways in which it might be tested in the future, we point out an avoidable conceptual error concerning emulation that Grush seems to share with other workers in the field, and we raise questions about the neural correlates of Grush's schemata that might be probed by neurophysiologists.
ABSTRACT Background: Interpreting the symbols found in the rock art of an extinct culture is hamp... more ABSTRACT Background: Interpreting the symbols found in the rock art of an extinct culture is hampered by the fact that such symbols are culturally determined. How does one break the circularity inherent in the fact that the knowledge of both the symbols and the culture comes from the same source? In this study, the circularity is broken for the Bradshaw rock art of the Kimberley by seeking anchors from outside the culture.Methods: Bradshaw rock art in the Kimberley region of Australia and Sandawe rock art in the Kolo region of Eastern Tanzania were surveyed in six visits on foot, by vehicle, by helicopter and from published or shared images, as well as from the published and online images of Khoisan rock art.Results: Uniquely shared images between Bradshaw and Sandawe art, such as the ‘mushroom head’ symbol of psilocybin use, link the two cultures and indicate that they were shamanistic. Therefore, many mysterious features in the art can be understood in terms of trance visualisations. A number of other features uniquely link Bradshaw and Sandawe cultures, such as a special affinity for small mammals. There are also many references to baobabs in early Bradshaw art but not later. This can be explained in the context of the Toba super‐volcano, the likely human transport of baobabs to the Kimberley and the extraordinary utility of the baobab.Conclusion: Many more mysterious symbols in Bradshaw rock art might await interpretation using the approaches adopted here.
Uploads
Papers by John Pettigrew
the D2/D4 ratio in the Palaeolithic artists has a much greater spread of values and a greater degree of sexual dimorphism. We find that living San people, who represent the minority of modern humans that have
high-variance genetics, also have a hand metric phenotype like the Palaeolithic artists, different from modern Europeans and other low-variance genetics modern humans. The increased variance and sexual
dimorphism of the phenotypic D2/D4 ratio in the San measurements are in keeping with genetic evidence that the San represent one of the oldest human lineages with the greatest genetic diversity. The findings have the implication that the European Palaeolithic cave artists may have been derived from San-like migrants who brought an established artistic tradition from Africa to Europe, only to be replaced as a population, leaving no evidence of their genetics in modern Europeans, as observed for other Palaeolithic genes such as Oase 1.
the D2/D4 ratio in the Palaeolithic artists has a much greater spread of values and a greater degree of sexual dimorphism. We find that living San people, who represent the minority of modern humans that have
high-variance genetics, also have a hand metric phenotype like the Palaeolithic artists, different from modern Europeans and other low-variance genetics modern humans. The increased variance and sexual
dimorphism of the phenotypic D2/D4 ratio in the San measurements are in keeping with genetic evidence that the San represent one of the oldest human lineages with the greatest genetic diversity. The findings have the implication that the European Palaeolithic cave artists may have been derived from San-like migrants who brought an established artistic tradition from Africa to Europe, only to be replaced as a population, leaving no evidence of their genetics in modern Europeans, as observed for other Palaeolithic genes such as Oase 1.