The Last Common Ancestor

In the last blog post I mentioned Sahelanthropus, who was potentially the first creature more human than ape. That leads us to a question that has had scientists scratching their heads for decades: What was the last common ancestor of us and chimps? Or, put more simply, what was the last species to evolve that gave rise to both humans and chimpanzees?

The date of the LCA split has been disputed from 5 to 13 million years ago, but based on other evidences like when gorillas split off and when fully bipedal hominins evolved we can safely put the date at 7 million years ago. Here, we have two main candidates: Sahelanthropus, who, again occupies a fickle position in our family tree, and Graecopithecus, a newly-discovered Miocene ape from Greece with little fossil material. Both of these have a lot of reasons against them.

If Graecopithecus is the LCA, then that would point to humans evolving in Europe and then moving to Africa. However, the rest of the fossils that we find from this time period are from Africa and there are no geographic intermediates. However, we cannot determine based on this whether Sahelanthropus is the LCA because there isn’t enough material to determine whether or not it was more human or not.

The LCA, whoever it was, gave rise to the first hominins, among which was Ardipithecus ramidus, the first ape to get bipedalism going. After “Ardi”, as the most complete specimen is known, came the genus Australopithecus, the first to master walking on two legs and to eat meat and use tools, and that’s what we’re going to be talking about in the next blog post.