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Bonobo, Pan paniscus. Credit: iStock |
A paper published a few days ago is bound to cause a frenzy of denialism amongst creationists of all varieties and not just because of the length of its title. It appears to confirm what many people have suspected for a very long time - that the closest living relative of Homo sapiens is the bonobo, Pan paniscus.
In fact, in some respects the difference between humans and bonobos is less than the difference between different varieties of creationist. Creationism has been evolving and diversifying at warp speed since its invention in the 19th century in response to the discovery by science of biological evolution.
Now the differences are so wide it's difficult to find two creationists who agree on anything very much. They can't agree on such basic as whether evolution occurs at all, whether it occurs at a fantastic speed or slowly, how intelligent an intelligent (sic) designer would need to be, how well or badly the evidence fits old religious myths, whether there is any value in scientific evidence. They can't even agree on what shape Earth is, how old it is and whether it orbits the sun or the sun orbits Earth.
In fact, it's rather good fun watching creationism trying to evolve furiously with no where left to run to, as the tidal wave of scientific evidence engulfs it like a global flood.
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Differences between head muscles of common chimpanzees, bonobos and modern humans. There are no major consistent differences concerning the presence/absence of muscles in adult common chimpanzees (left) and bonobos (center), the only minor difference (shown in grey in the common chimpanzee scheme) being that the omohyoideus has no intermediate tendon in bonobos, contrary to common chimpanzees (and modern humans). In contrast, there are many differences between bonobos and modern humans (right) concerning the presence/absence of muscles in the normal phenotype (shown in colors and/or with labels in the human scheme). See paper for more details.* Click image to enlarge |
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Differences between forelimb muscles of common chimpanzees, bonobos and modern humans. The only consistent difference between bonobos (center) and common chimpanzees (left) concerning the presence/absence of muscles (shown in colors in the common chimpanzee and bonobos schemes) is that in the former the intermetacarpales 1–4 are usually fused with the flexores breves profundi 3, 5, 6 and 8 to form the dorsal interossei muscles 1–4 (* in bonobo) figure, as is the case in modern humans. In contrast, there are many differences between bonobos and modern humans (right) concerning the presence/absence of muscles (shown in colors and/or with labels in the human scheme; muscles present in chimpanzees and not in humans are shown in black, in chimpanzees). See paper for more details.* Click image to enlarge |
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Differences between hindlimb muscles of common chimpanzees, bonobos and modern humans. The only consistent difference between bonobos (center) and common chimpanzees (left) concerning the presence/absence of muscles (shown in colors in the common chimpanzee scheme) is that the latter usually lack the scansorius, as is the case in humans. In contrast, there are many differences between bonobos and modern humans (right) concerning the presence/absence of muscles (shown in colors and/or with labels in the human scheme; muscles present in chimpanzees and not in humans are shown in black, in chimps). See paper for more details.* Click image to enlarge |
The paper, published open access in Scientific Reports a couple of days ago by scientists from the Department of Anatomy, Howard University College of Medicine, Washington, DC, USA and Department of Anthropology, George Washington University, Washington, DC, USA show that there have only bee four minor changes in the bonobo's musculature since they split of from our last common ancestor.
From studying the anatomy of seven bonobo cadavers from Antwerp Zoo it was clear that the common chimpanzee, Pan troglodytes, has diverged most and the bonobo least from the last common ancestor of all three species.
Abstract
Common chimps and bonobos are our closest living relatives but almost nothing is known about bonobo internal anatomy. We present the first phylogenetic analysis to include musculoskeletal data obtained from a recent dissection of bonobos. Notably, chimpanzees, and in particular bonobos, provide a remarkable case of evolutionary stasis for since the chimpanzee-human split c.8 Ma among >120 head-neck (HN) and forelimb (FL) muscles there were only four minor changes in the chimpanzee clade, and all were reversions to the ancestral condition. Moreover, since the common chimpanzee-bonobo split c.2 Ma there have been no changes in bonobos, so with respect to HN-FL musculature bonobos are the better model for the last common ancestor (LCA) of chimpanzees/bonobos and humans. Moreover, in the hindlimb there are only two muscle absence/presence differences between common chimpanzees and bonobos. Puzzlingly, there is an evolutionary mosaicism between each of these species and humans. We discuss these data in the context of available genomic information and debates on whether the common chimpanzee-bonobo divergence is linked to heterochrony.*
However, the closeness of bonobos to humans doesn't so much reflect the chronology of the split as the fct that since then, bonobos have changed the least. This means that they are probably more representative of our common ancestor than is the common chimpanzee, P. troglodytes, or H. sapiens. In fact scientists believe that Homo and Pan lineages split about 8 million years ago with the two Panids diverging about 2 million years ago. As common chimpanzees and bonobos evolved after their split, they developed differently, separated as they were by the Congo River.
In addition, our study has shown that there is a mosaic evolution of the three species, in the sense that some features are shared by humans and bonobos, others by humans and common chimpanzees, and still others by the two ape species. Such a mosaic anatomical evolution may well be related to the somewhat similar molecular mosaic evolution between the three species revealed by previous genetic studies: each of the chimpanzees species share about 3 percent of genetic traits with humans that are not present in the other chimpanzee species.
Rui Diogo, lead author
Associate professor of anatomy at Howard University.
(Quoted in George Washington University press release.)
It was also clear that there is a great deal of what scientists term 'mosaicism' in all three species reflecting not only the closeness of our relationship and relative recency of the split. It also suggests that the split was by no means sudden and that all three species continued to interbreed and so exchange genetic material for some considerable time.
Earlier studies, reported on in this blog, suggested that humans and chimpanzees continued to interbreed occasionally for maybe 2 million years as the species diverged, going through regional variety, subspecies, species with occasional interbreeding ability and finally full species status. So too did the panids.
In fact, just as with later hominid evolution, where different related species of Homo interbred and the complex of divergent species acted like a ring species, so it seems early Hominins and Panids also behaved similarly.
*© 2017 Macmillan Publishers Limited/The AuthorsOpen Access.
Reprinted under the terms of a Creative Commons Attribution 4.0 International License (CC-BY 4.0)
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