[一日遊] moly! he thought

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Common chimps were the perfect place to start. Not only are they a classic example of the walkinganimal, but they’re also our closest living relative; after more

than six million years of separateevolution, 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, chimpsdon’t. We have very different feet: ours are arched, chimps’ are flat. Our toes are short

andstraight, which helps running, while chimps’ are long and splayed, much better for walking. Andcheck out our butts: we’ve got a hefty gluteus maximus, chimps

have virtually none. Dr. Bramblethen focused on a little-known tendon behind the head known as the nuchal ligament. Chimpsdon’t have a nuchal ligament. Neither do

pigs. Know who does? Dogs. Horses. And humans.

Now this was perplexing. The nuchal ligament is useful only for stabilizing the head when ananimal is moving fast; if you’re a walker, you don’t need one. Big

butts are only necessary forrunning. (See for yourself: clutch your butt and walk around the room sometime. It’ll stay soft andfleshy, and only tighten up when you

start to run. Your butt’s job is to prevent the momentum ofyour upper body from flipping you onto your face.) Likewise, the Achilles tendon serves nopurpose at all  with her, he would sanction
everything at oncehe answered.


in walking, which is why chimps don’t have one. Neither did Australopithecus, oursemi-simian four-million-year-old ancestor; evidence of an Achilles tendon only

began to appeartwo million years later, in Homo erectus.

Dr. Bramble then took a closer look at the skulls and got a jolt. Holy . There’ssomething going on here. The back of the Australopithecus skull was

smooth, but when hechecked Homo erectus, he found a shallow groove for a nuchal ligament. A mystifying butunmistakable time line was taking shape: as the human body

changed over time, it adopted keyfeatures of a running animal.


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