Ardipithecus ramidus

Illustration by J.H. Matternes; graphic by The Washington Post (Oct. 1, 2009)

Illustration by J.H. Matternes; graphic by The Washington Post (Oct. 1, 2009)

Ethiopian paleoanthropologist Yohannes Haile-Selassie has discovered an interesting biological clue about our hominid ancestors.  They lacked a few of the traits that we associate with modern day ape-ness:

The story of Ardi takes us back 4.4 million years to a corner of northeast Ethiopia that today is a desert where erosion constantly exposes fossils from the dawn of humankind.

In all, scientists have discovered fossilized bones and teeth in the area representing three dozen individual Ardipithecus specimens, including much of Ardi’s skull, pelvis, lower arms and feet. Until now, Haile-Selassie says, much of what we knew about our ancient past derived from comparisons with the other apes, and especially chimps, and from Ardi’s younger ‘sister’ — Lucy, the 3.2-million-year-old specimen of another hominid species, Australopithecus afarensis, discovered in 1974, also in Ethiopia. Lucy’s discovery showed that human forebears walked upright that long ago.

But Ardi, Haile-Selassie says, shows our first erect steps took place more than a million years earlier and that is much closer to the last common ancestor (or LCA) that the human line shares with the ape line after the two split some six million years ago.

Until now, it has been assumed chimps and gorillas have retained many of the supposed traits of that last common ancestor, among them knuckle-walking and climbing ability.

Now, Haile-Selassie says, we know that isn’t true.

Ardi shows that unlike modern apes, which are knuckle-walkers, her species — and by extension all the ancestors of all apes and humans — descended from a common ancestor that in turn was not a knuckle-walker, he says.

…The researchers say the surprising findings mean chimps and gorillas have specialized greatly since then and are poor models for a common ancestor and for understanding human abilities such as walking.

— Meaney, Ken.  “Evolution: Discovery may change the way we think about evolution, ourselves.” Canwest News Service, 3 October 2009.  [Emphasis mine]

This further underlines the somewhat little-understood distinction that humanity is not descended from “monkeys”, but that apes and humans shared a common ancestor. It’s a big difference, and it’s important to remember that a lot of the ape traits that we see today actually evolved long after our developmental paths began to diverge.  So while we can learn something from our modern simian relatives, they offer limited utility in understanding how we developed the unique capabilities that make us Homo sapiens.  For that we have to go to the fossil record and continue to mine our own history.

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