Winnie Lim

Common chimps were the perfect place to start. Not only are they a classic example of the walking animal, but they’re also our closest living relative; after more than six million years of separate evolution, we still share 95 percent of our DNA sequence with chimps. But what we don’t share, Bramble noted, is an Achilles tendon, which connects the calf to the heel: we’ve got one, chimps don’t. We have very different feet: ours are arched, chimps’ are flat. Our toes are short and straight, which helps running, while chimps’ are long and splayed, much better for walking. And check out our butts: we’ve got a hefty gluteus maximus, chimps have virtually none. Dr. Bramble then focused on a little-known tendon behind the head known as the nuchal ligament. Chimps don’t have a nuchal ligament. Neither do pigs. Know who does? Dogs. Horses. And humans.