I hope you watched “Discovering Ardi” on Discovery Channel last Sunday evening. If you missed it, be sure to watch the repeat on October 15th. It’s a fascinating two-hour tale of a fifteen-year adventure:
Human-like fossil bones, 4,000,000 years old, dug up in
Ethiopia. A whole collection of such bones from a single
female, painstakingly extracted from a site nearby.
Preservation and examination of those bones.
Reconstructions of the body, locomotion, environment, and
life of this creature. Hypotheses about the selective
pressures that may have produced her species.
It would be hard to pick a “best” part of this story. But if I had to choose, my choice would have to do with Ardi’s feet and her way of getting around.
Until Ardi, the general belief in biology about human evolution has been that we evolved on the savannahs of East Africa. Savannahs are an ecosystem of grass and trees. The trees are far enough apart that a savannah feels mostly like grassland. Biologists thought the savannah could have favored our special human form of locomotion, bi-pedalism. That is, we walk upright on two legs. This is in contrast to our nearest relatives, the chimps and gorillas, who are knuckle-walkers, not fully four-legged, not really two-legged.
The savannah argument had us upright in order to see over the grasses. That way we could look for game to kill and eat, and we could see predators before they saw us. Our upright posture would have accompanied continual improvement in distance vision. And since we would have been traversing grassland rather than swinging in trees, our feet would have evolved the shape they have now, the apelike thumb and its joint changing into a big toe. Being upright would have freed our hands, so natural selection could have begun favoring near vision, hand-eye coordination, and a bigger and bigger brain, all of which could have led to tool production.
Tra-la, wrong. Here’s Ardi, definitely bi-pedal; you can tell from her pelvis and hip joints; definitely a hominid. But she had grasping feet. That’s right, thumbs on her feet, just like our ape cousins.
So the paleontologists and evolutionary biologists who found her went back and combed the site for other fossils of plants and animals to figure out the ecosystem Ardi lived in: Forest. Not savannah. Forest. Ardi was a very early hominid, and she was comfortable in trees as well as on the ground.
Therefore, as has happened so often in in biology, the facts have come along to show us that, as brilliant as we thought we were, we weren’t. I’ll have more to say about this in my next blog.