![]() She didn't walk like an upright chimpanzee. They had a slightly flatter foot than we do, but if you could see Lucy just walking along at a distance, you wouldn't really notice a difference. They transferred a lot of their weight to their big toe, like we do. So from the footprints and the skeletons, we can infer from their gait that how they walked was a lot like ours. Her species even left us these extraordinary footprints in Tanzania known as the Laetoli footprints. With the famous Lucy, not only do we have her skeleton, but we have bones of lots of other individuals that were found near her. Human footprints discovered at Laetoli, a pre-historic site located in Tanzania. And there were different experiments going on in how to move from point A to point B. But it could be that uprightness goes back further than we once thought. It seems like there would be a better way to live in trees than standing on two legs. SP: Standing upright in trees sounds really counterintuitive. ![]() But what we're finding is these apes tend to be somewhat upright in the trees, holding onto branches above them and moving on two legs in the trees. They love trees that are producing fruit. The forests of Africa in this time period had spread north and hugged what is today the Mediterranean. They're from apes that were living in southern Europe - in France and Italy and Spain, Greece, Turkey. We don't have many, but what fossils we do have are not from knuckle-walkers. ![]() Now we can test this idea by looking at fossils from that time period, 6 to 10 million years ago. One of the hypotheses for years and years is that the common ancestor we shared with chimpanzees would have been a knuckle-walker, and that bipedalism evolved later. When they're getting around, they're usually on all fours, with the knuckles on the front hands down on the ground. They can't support their bodies on a single leg, so they fall over and they wobble. JDS: They can get up on two legs, but it's not a very efficient form of locomotion for them. SP: And yet our closest relatives - chimpanzees and gorillas - are not actually bipedal. All these things really have their roots in how we move. It set the stage for all the things that happened later, from our language and our dietary flexibility, to our reliance on technology and tools, to the way we give birth and raise our children. SP: So walking upright is essentially what made us human? ![]() Bipedalism is the most ancient human adaptation. They weren’t using sophisticated technology, and they weren’t talking. Jeremy DeSilva: What we can tell from studying these fossils is that the earliest members of our lineage didn’t have large brains like we have today. Steve Paulson: What do these fossils tell us about our evolutionary history? This interview has been edited for length and clarity. Steve Paulson with Wisconsin Public Radio's "To the Best of Our Knowldge" went to Dartmouth College to visit DeSilva in his basement lab, where he has drawers full of replicas of all the great fossil discoveries about human evolution. He outlines this argument in his book "First Steps: How Upright Walking Made Us Human." There’s still a lot we don’t know, but DeSilva is convinced about one thing: our ancient ancestors walked upright - and that changed everything. This requires meticulous detective work - finding a skull here, a bone there - and then reconstructing how these creatures moved around, found food and avoided giant lions and hyenas. He’s trying to crack the mystery of how exactly we evolved from a small ape living in trees to the species that would come to dominate the Earth. Paleoanthropologist Jeremy DeSilva loves fossils, especially remnants from our ancient hominin ancestors. ![]()
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