Following on from last week’s installment about the pelvis, I’m going to take a look at the adaptations of the thigh bone (femur) to upright walking.
One of the most important requirements of being able to walk efficiently is keeping your body’s centre of mass (CoM) above your base of support (essentially the size of the area of ground your feet enclose when standing; fig. 1). This is especially important in upright walking since the base of support is so much smaller than for a quadrupedal animal.
Figure 1. Showing the relationship between centre of mass and base of support in a knuckle-walking chimp and an upright human.
Quite a while ago, I wrote a monster double post on something called the Chimpanzee Referential Doctrine, over which a two-sided debate continues to rage. The old guard of palaeoanthropology firmly believe that we can tell a lot about our ancestors from observing the anatomy, environment and behaviour of modern chimpanzees, while more and more people are adopting the viewpoint that our earliest ancestors were distinctly un-chimp-like. There’s also a question which constantly does the rounds of people curious about evolution or those trying to push Creationism: “if we evolved from monkeys/chimps then why are there still monkeys/chimps?”
In the next few posts, I hope the answer will become clear: we evolved from something that was neither human-like nor chimp-like, but gave rise to both.