Did our ape ancestors really fall out of the trees? / Updated

New paper added at bottom, below large illustration. 

The usual story of human evolution goes like this:

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There were apes living in the forest just like chimpanzees do today, but something happened to make the trees go away, and the apes were forced to stay on the ground and eat grass instead of nuts and fruits. Why this only affected that particular ape, and not the other creatures in the forest, is ignored. Anyway – at times there were trees nearby, and the apes ran back, climbed the trees and like yoyos ran back and forth between habitats until they could walk on two legs.

What happened next is usually glossed over, but the apes end up walking around as savannah-living, walking, running, obligate bipeds who scavenge or hunt meat, having switched from eating grass, like a cow, to digesting meat, like a lion.

The problem is that most of this story is based on equating “us” (modern Homo sapiens) with the chimpanzee, which is not our ancestor. Our ape ancestors diverged from chimpanzee ancestors 5-7 m.y.a. – that’s what a split is. Their ancestors evolved into the chimpanzees we see today – living in tropical forests. Our common ancestor before the split was not a modern chimpanzee or a modern human. This mistake of confusing species that exist today with archaic forms is so egregious, that it makes talking about evolution nearly impossible.

Another example: Bipedalism dates back at least 3-4 million years ago, and that date is possibly conservative. Homo sapiens did not “become bipedal” – our ape ancestors evolved a bipedal habit. Homo sapiens is an obligate biped!

It is entirely possible that our ape ancestors were ground dwellers, not tree dwellers.

It makes far more sense to begin with a ground dwelling ape than to conjure a bipedal animal directly from a tree-swinging one – the structural changes are daunting, which doesn’t account for all the brain changes necessary to  reorganize how the body orients itself in space; balances gravitational force, coordinates muscles, reorients vision, etc. But here we are, stuck with a torturous scenario (and in a New York minute!) that must turn a shared chimpanzee blue print into a human blueprint.

It should be obvious that modern humans, archaic humans and our bipedal ape ancestors departed on distinct evolutionary path compared to chimpanzees, gorillas and orangutans, and yet the chimpanzee is a favorite model for the evolution of modern Humans.
Reconstruction of Australopithecus sediba ape skeleton 2 m.y.a. compared to those of a modern human (left) and a modern chimpanzee (right).

Reconstruction of Australopithecus sediba ape skeleton 2 m.y.a. compared to a modern human (left) and a modern chimpanzee (right).

 

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Neither chimpanzee nor human, Ardipithecus reveals the surprising ancestry of both

Tim D. White, C. Owen Lovejoy, Berhane Asfaw, Joshua P. Carlson and Gen Suwa

Abstract / Australopithecus fossils were regularly interpreted during the late 20th century in a framework that used living African apes, especially chimpanzees, as proxies for the immediate ancestors of the human clade. Such projection is now largely nullified by the discovery of Ardipithecus. In the context of accumulating evidence from genetics, developmental biology, anatomy, ecology, biogeography, and geology, Ardipithecus alters perspectives on how our earliest hominid ancestors—and our closest living relatives—evolved.

Charles Darwin famously suggested that Africa was humanity’s most probable birth continent, but warned that without fossils, it was “…useless to speculate on this subject” (2). Nevertheless, Darwin and his less cautious contemporaries and intellectual descendants used humans and modern apes to triangulate ancestral anatomy and behaviors, which promulgated the erroneous metaphor of a hominid “missing link.” Even today, despite thousands of available fossils, this deeply embedded metaphor reinforces the misconceptions that extant apes—particularly chimpanzees—can be viewed as “living missing links,” or that that modern African apes combined can be used to represent the past “as time machines” (3).

The notion that modern great apes are little changed from the last common ancestors we shared with them promoted the assumption that hominid fossils anatomically intermediate between living apes and ourselves would eventually be found. Now, however, long sought and recently discovered African fossils provide escape from such persistent but inaccurate projection. These paleontological discoveries do not yet include the common ancestor we shared with chimpanzees (the CLCA). However, they substantially reveal the early evolution of the hominid clade (the term “hominid” denoting all species on the human side of the human/chimpanzee phylogenetic split). These fossils have begun to rectify the mistaken notion that contemporary apes, in particular common chimpanzees, can serve as adequate representations of the ancestral past.

Much, much more!

 

One thought on “Did our ape ancestors really fall out of the trees? / Updated

  1. If you explore the posts in my blog you will find critiques of specific studies and ideas, not only by me, but from many scientists and science writers. As an Asperger I “pick on” psychologists, but I am honestly amazed at how much bad science is spread to the public, especially via the internet. It’s a real problem. I spend many hours investigating “research” that is presented as science: you can watch these articles proliferate – and become “truth” of the minute, with no one questioning the validity of methods, conclusions and reporting. In this case I am criticizing the argument structure: the same old outdated storyline is simply repeated over and over with “new” info inserted to make it seem valid or more important than it is. There is no way to scientifically validate such stories.

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