Humans and chimps split from each other 7 - 14 million years ago. What did those first members of the human family look like?
Since chimps and other apes are all relatively similar; it was thought that represented the "default" condition. Thus, the first members of the human family (called hominins) should actually be quite chimp-like. Hairy, rainforest dwelling primates that didn't walk upright and with a fondness for fruit ( and maybe murder)
However, a recent review of early hominin fossils has revealed that they were actually a lot less chimp-like than was expected. Researchers examined Ardipithecus ramidus; one of the earliest hominin fossils we have. This African fossil clocks in at 4.4 million year ago and is certainly very ape-like. It lived in the trees and had a small body and brain.
Yet when they compared it directly to chimps they found a lot less similarities than you would expect. So whilst the earliest members of the human family were very ape-like; they weren't that similar to chimps specifically. These early humans/apes were something else entirely.
This is very significant since chimps are often used as models for research into human evolution. When we identify the circumstances that a chimp walks upright we might think that those circumstances are what drove our ancestors to walk upright.
What about isn't Ardi chimp-like?
Well, almost everything. Some of the key differences include:
- Ardi lived in open woodland, whilst chimps prefer tropical rainforest.
- Ardi didn't knuckle-walk like chimps; instead opting for a mixture of clambering on all fours, swinging through the trees and walking upright
- Ardi's teeth and head aren't very chimp-like; lacking their adaptations for a fruit-based diet.
- Ardi lacks chimps' self-sharpening teeth, suggesting they may not have been as violent as their close relatives
Plus, a whole hose of anatomical differences associated with these characteristics (such as changes to Ardi's hip that allowed them to walk upright).
Are chimps and Ardi still related?
Of course they are! The evidence for chimps being our closest living relatives is overwhelming. What this research indicates is that modern chimps have changed quite a lot over their evolution; they aren't living "missing links". It's just like how we've changed a lot since Ardi. Both chimps and humans evolved from a common ancestor that was quite different to these modern species.
Reference
White, T. D., Lovejoy, C. O., Asfaw, B., Carlson, J. P., & Suwa, G. (2015). Neither chimpanzee nor human, Ardipithecus reveals the surprising ancestry of both. Proceedings of the National Academy of Sciences, 112(16), 4877-4884.
