Just-so stories are prominent in human evolution literature because of our tendency to create simple progressionist narratives about our “special” place in nature, despite the fact that these stories are almost exclusively based on hard tissue data. How can we be so certain about the evolution of human facial communication, bipedalism, tool use, or speech without detailed knowledge of the internal anatomy of for instance, one of the two extant species more closely related to us, the bonobos? Here I show how many of these stories now become obsolete, after such a comprehensive knowledge on the anatomy of bonobos and other primates is finally put together. Each and every muscle that has been long accepted to be “uniquely human” and to provide “crucial singular functional adaptations” for our bipedalism, tool use and/or vocal/facial communication, is actually present as an intra-specific variant or even as normal phenotype in bonobos and/or other apes.
Paper freely available here: https://www.frontiersin.org/articles/10.3389/fevo.2018.00053/full
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This is a very important paper in my opinion. It shows that many of the so-called "human" features in humans and fossil Homo are not human-derived, but are hominid-primitive or even hominoid-primitive, i.e. were already seen in the Mio-Pliocene ancestors and relatives of some or all living apes and humans. Diogo here shows this clearly for different muscular features, but we already argued this for several skeletal features, e.g. there are different indications that all or some early hominids (i.e. extinct relatives of Pan, Homo and Gorilla such as the australopithecines) were already orthograde (i.e. with vertical lumbar spine) and possibly even bipedal, probably not for running in African savannahs as often assumed traditionally and anthropocentrically, but more likely not only for climbing vertically but also for wading bipedally in the flooded forests or wetlands where many or even most Mio-Pliocene hominoids including the austalopithecines apparently fossilized (e.g. Verhaegen, Puech & Munro 2002 "Aquarboreal Ancestors?" Trends in Ecology & Evolution 17:212-7).
Diogo asks whether the muscular features he describes are no adaptations, but possibly by-products of other features. If we consider a possibly more climbing-wading locomotion (orthograde aquarborealism) for the early hominids or even hominoids, as exemplified by bonobos or lowland gorillas when wading bipedally in forest swamps (google e.g. "bonobo wading" or "gorilla bai"), it may well be that at least some of Diogo's findings do not have to be explained as evolutionary by-products, but simply as adaptations to the original hominid and/or hominoid environment (google e.g. "Ape and Human Evolution 2018 made easy" or "not Homo but Pan naledi? 2018").
Thanks Marc. It is in fact striking to see that in history of sciences we tended to do the mistake of thinking we are unique in almost everything, and even now that we realize those mistakes, most people cannot avoid thinking within that erroneous framework.. it will take some time (and buzz) to change that, but it will be done, soon..
:-) Thanks, Rui. The great anatomist Adolph Schultz (who dissected in his long career hundreds of apes and monkeys, but no bonobos as far as I know) already described many unexpected apelike features "retained" in human anatomy (in adult and/or premature humans). Thank you very much for your beautiful and detailed work on bonobo anatomy, which seems to confirm that the traditional idea that human ancestors became bipedal by evolving directly from forest- to open plain-dwelling is at least much too simplistic (anthropocentric).
More likely in my opinion (please google my recent update "Ape and Human Evolution 2018 biology vs anthropocentrism") is that the early "apes" (Miocene hominoids) adapted to living in flooded forests (possibly mangrove or swamp forests or wetlands), and that, much later, Plio- or early-Pleistocene Homo adapted "further" to a littoral lifestyle (Coastal Dispersal Model, e.g. S. Munro 2010 Molluscs as Ecological Indicators in Palaeoanthropological Contexts, PhD thesis Canberra University) - which helps explain not only the "fast" intercontinental diaspora of "archaic" Homo (along African and southern Eurasian coasts, and later also rivers), but also, for instance, Homo's drastic brain enlargement (littoral foods are extremely rich in brain-specific nutrients such as DHA, see e.g. S. Cunnane 2005 Survival of the Fattest, World Scientific).
Very interesting ideas. I will read your update right now
you know also another funny story, normally i have no problem at all publishing papers, in fact i think none of my last 30 papers or so were refused, and they go to top journals such as Nature, Evolution, Biol Rev, etc.. with one exception.. this one, which was refused in 4 or 5 journals.. I wonder why.. :) .. same style, same kind of images.. but story criticizes many a way of thinking that has been prevalent in a field, Bioanth, which is remarkably conservative, scientifically.. so it is good some people, like us, try to change that.. ok, will read your update now..
Yes, Rui, it's difficult to understand that you had so many problems in getting this very important paper published. The field of (paleo)anthropology is remarkably conservative and anthropocentric (just so). Traditional anthropological journals still happily publish papers on so-called adaptations of "hominins" (assuming, without scientific evidence, that australopithecines are closer relatives of Homo than of Pan or Gorilla) to running or using tools or even hunting in African savannahs (assuming, again without evidence, that quadru->bipedality = forest>open plain), but are reluctant to publish papers questioning these dogmas.
Since several decades, different students have argued (independently!) that some or all australopithecines might have been more bipedal and/or orthograde than extant apes, and might be closer relatives of Pan or Gorilla than of Homo (e.g. my paper "Australopithecines: Ancestors of the African Apes? Human Evolution 9:121-139, 1994). Nevertheless, traditional anthropologists keep assuming dogmatically that australopiths had already evolved in the human direction (together "hominins"), instead of considering the more parsimonious view that both humans and African apes had more australopith-like ancestors and then evolved in different directions, Pan and Gorilla (in parallel) becoming knuckle-walkers (less bipedal), and Homo becoming more bipedal (possibly for more frequent wading, rather than for running over open plains). For a recent example of extreme anthropocentrism, google e.g. "not Homo but Pan naledi? 2018".