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Out & About: Dartmouth professor talks the walk, how humans became upright

  • Liz Sauchelli. Copyright (c) Valley News. May not be reprinted or used online without permission. Send requests to permission@vnews.com.

Valley News Staff Writer
Published: 4/3/2021 9:41:29 PM
Modified: 4/5/2021 4:41:36 PM

We’ve all seen the illustrations of human evolution, where a knuckle-walking chimpanzee on the left gradually transforms into an upright-walking human on the right. It’s a straightforward explanation of how we got from Curious George to George Clooney.

But like so much else, the truth of how humans evolved to walk on two legs is far more nuanced. It’s also the topic of a new book by Dartmouth College professor Jeremy DeSilva titled First Steps: How Upright Walking Made Us Human, which he will discuss from 7 to 8 p.m. Tuesday during a virtual program hosted by the Montshire Museum of Science. People can register for the free program at montshire.org/calendar/event-detail/author-talk-first-steps.

“One of the things I loved about writing this book was my audience for the book was the general public, not my colleagues, and it was really intentional on my part,” said DeSilva, who previously worked as an educator at the Boston Museum of Science. “It took a while to reconsider that voice, how to write for someone who doesn’t think about human evolution every day like I do. Once I rediscovered that voice, it was just a really enjoyable process to write this book.”

DeSilva, an associate professor of anthropology at Dartmouth, has focused his area of study on hip, foot and leg bones of our earliest ancestors. One misconception people have — like that popular image portraying evolution — is that evolution is linear and we went from knuckle-walking to upright walking without any deviation. It didn’t happen that way.

“You’d find these different species of humans coexisting and walking in different ways,” DeSilva said. Fossils found throughout the world backed that up. “All of these things didn’t happen in lockstep with each other. Evolution doesn’t work by gradually transforming an ape into a human.”

In writing the book, DeSilva put together a MOOC — massive open online course — with help from Dartmouth staff, that thousands of people took titled “Bipedalism: The Science of Upright Walking.”

“It was so great to organize my thoughts and think about, ‘What are the big issues here? Why should people care about upright walking?’ ” he said.

The main conclusion he came to was this: “We’re the only mammals who do this all the time.”

“Whenever another mammal walks on two legs, we lose our minds,” he said, citing a viral video from a few years ago of an upright-walking gorilla named Louis at the Philadelphia Zoo. “These things together to me told this very fascinating story of something that we think is ordinary is actually really awesome and remarkable and set the stage for so many other things that make us human.”

During a sabbatical, DeSilva traveled to view fossils at the labs of other colleagues. He met with researchers who study what motivates children to walk on two legs when they are just as fast — if not faster — on four. He learned about how different cultures approach walking on two legs differently, with some encouraging kids to start younger and others wait until they’re older.

“There’s so much plasticity around the human form and the onset of walking,” DeSilva said.

Humans also weren’t the only species to ever walk upright: Discovered in North Carolina and dating back around 231 million years, a fossil of a crocodile nicknamed the “Carolina Butcher,” has bones showing that it primarily walked on its two back legs.

“Their ancestors were up on two legs sprinting. Their bones tell us that they could move on two legs and yet that was not a successful form of locomotion,” DeSilva said. “It probably couldn’t stealth-hunt, so that lineage became quadrupedal and lying in the bushes on all fours and waiting for something to come closer and then attack.”

DeSilva also looks at the physiological benefits of walking and how everyone has a different gait — you can tell someone’s mood from the way they walk.

“We’ve always been walkers, and what’s different now is not walking. In order to get food, in order to find water, in order to move camps for hundreds of thousands of years, we have walked,” DeSilva said. “We are a walking species. It’s only recently that we’ve become sedentary and sluggish and that walking has become a chore, and there have been real physiological effects.”

While other species such as emus and ostriches do walk upright, humans are the only mammals who regularly do so.

“I think a lot of people think that bipedalism confers so many advantages, and that’s true to an extent, but if that were entirely true, it would be a locomotion that would evolve over and over again and persist, and it doesn’t,” DeSilva said.

The bones DeSilva and others have studied also tell another story: one of compassion. Fossils of earlier humans have been found to have healed leg fractures. Instead of being left behind for dead by the group they traveled with, they survived.

“To me, it’s clear evidence that we took care of each other,” DeSilva said. “We are compassionate. We are caring. We are empathetic and when someone is injured, we help them out, and we’ve been doing that for millions of years, and it’s intimately tied to upright walking.”

Liz Sauchelli can be reached at esauchelli@vnews.com or 603-727-3221.

Correction

Jeremy DeSilva, an associate professor of anthropology at Dartmouth College, said a fossil indicates that some crocodiles once walked primarily on their two back legs but became “quadrupedal,” using all four legs for locomotion, over time. An earlier version of this story incorrectly quoted DeSilva. 

  




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