Astonishing fossils are found every year, but the original “missing link” remains as hopelessly elusive as ever. Where is the last common ancestor of humans and chimps? “I would love to know,” says of the George Washington University in Washington DC. “That question is keeping me awake at night.”
On the face of it, there is good reason to think that the last creature from which both humans and chimps – our closest cousins – can claim descent might eventually be found. After all, we have a pretty good idea when and where it was dragging its knuckles, or swinging through the trees. “It is universally accepted that the last common ancestor of chimps and humans lived in Africa, probably around 7 million years ago,” says of the Catalan Institute of Palaeontology in Barcelona, Spain.
The bad news is that any evidence of this animal will be very, very hard to find. After decades of searching we have a reasonably rich collection of fossils of our hominin ancestors, stretching back 4 million years. But fossil evidence of anything earlier than that would barely fill a couple of shoe boxes.
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There are many reasons for this, says at the University of California, San Francisco. “Hominins are comparatively more abundant both because they began living in regions that are more likely to fossilise, like lake shores and caves, and there are a lot more people actively searching for them.” Our earlier ancestors were fewer and further between, and would have left traces in less predictable places.
We might not even know them if we saw them. “One thing that worries me: since different scholars have very different expectations of how this ancestor looked, will we be able to recognise it for what it is in the hypothetical case that we find it?” asks Almécija.
By comparing early hominin fossils, ape fossils and large numbers of living primates, Almécija thinks our forebear had and bones that were more human-like than chimp-like. It probably still walked on all fours, he says, but not in the way that chimps do. Young and his colleagues have used a broadly similar approach to suggest that the – suggesting it swung through the trees like chimps do today.
Almécija thinks it is possible this ancestor had a combination of features – and maybe even some seen in neither group today. One hope is that comparing the genomes of living apes might provide evidence everyone can agree on.
There is a big caveat, however. All this assumes that there was a single ancestor. Genetic studies so far hint that some of our chromosomes , possibly indicating that there wasn’t a simple, clear split. Rather, primate-like populations separated for a time, came back together and hybridised, before they split permanently – all of this over the course of millions of years. Try picking a single ancestor out of that tangled mess.
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