The National Geographic and the news services are touting a new ape fossil found in Ethiopia as “forcing a rethink on human evolution”. As usual, the headlines are hyperbolic. This ape is fragmentary, and so far only teeth and a jaw bone have been found, and the teeth are similar to gorilla teeth. Gorillas are thought on molecular grounds to have split off from the chimp-human clade about 7 million years ago, but this specimen is 10 million years old. What gives?
I can think of a couple of options. One is that, as I have reported previously, teeth are not great diagnostic material for phylogeny. They are very adaptable, and if a species finds itself in a similar environment with a similar diet, the teeth will tend to evolve rapidly to a particular morphology similar to that of relatives who later evolve in the same situation.
Another is that the ancestral state (called a plesiomorphy, from the Greek for “neighbour” + “form”) may have had teeth rather like this, and the chimp/human dental formula is the derived one. Non-human ape fossils are rather rare, so we may not know this. If it is true, then this species may have diverged millions of years before the chimp/human lineage split from the gorilla lineage.
One of the things that greatly bothers me about how the media frame this sort of thing, is that every revision to what is, after all, a historical claim rather than a theoretical one about the process by which we or any other species evolved, is called a “major reformulation”. It’s as if the origins of the United States was found on the basis of new evidence to have derived from German-speaking settlers rather than English speaking ones; the story about the origins of the USA would change, but not the idea that the USA arose in a historical fashion. Creationists of course leap onto these headlines as evidence that evolution isn’t true, when in fact this is further evidence that the evolutionary model is fruitful and sensitive to evidence. The USA did not exist for all time, and neither did the present ape species.
History is hard to grasp if the evidence is not there. Finding out that Washington never chopped down the cherry tree ought not cause people to deny that Washington existed, and finding out that things occurred somewhat differently to earlier hypotheses in human and ape evolution doesn’t undercut the idea of evolution itself. New evidence is welcomed in biology, if not in religiously motivated ideologies.
Late note: John Hawks has a nice review of the paper here.