Jeremy DeSilva, anthropologist: “Empathy and compassion compensated for the physical limitations of a bipedal creature” | Science

Over the course of a lifetime, the average person takes about 150 million steps. Enough to circle the Earth three times. We may not realize it, but our gait—bipedal and upright—is a fairly rare phenomenon in nature, unique among mammals. Jeremy DeSilva (Attleboro, Massachusetts, 48) is an American anthropologist obsessed with human evolution as seen through the lens of bipedalism. He is part of the research team that discovered two ancient members of the human race: Australopithecus sediba And Homo naledi. He also studied wild chimpanzees in western Uganda and primitive fossils in museums in eastern and southern Africa. All this to answer a single question: how did walking upright make us human?

DeSilva searched everywhere for answers. Their analysis of the feet allowed us to reconstruct the motor skills of the first apes and our first hominid ancestors. Now he published in Spanish Step by step (Captain Swing) a book that combines history, science and culture to explore how walking on only two limbs allowed humans to become the dominant species on the planet. The scientist answers EL PAÍS’s questions via video call from his office at Dartmouth College (New Hampshire, USA) and remains standing throughout the interview.

Ask. Do you usually spend a lot of time on your feet?

Reply. As a scientist, you have to be as objective as possible, collect data and observe it from a distance. But the reality is that scientists do science, and scientists are people. The questions we ask affect us. I have been studying this topic and since writing the book I have been taking walks every day. I try to stay active. Some of these things include using a standing desk, like the one I have now, instead of sitting. Although there is recent data that shows that this is not so profitable.

TO. Throughout your career as an anthropologist, you have asked yourself many questions about our extinct human ancestors. Why did you ultimately decide to study upright walking?

R. As an anthropologist, I am interested in the unusual aspects of humans. One is a form of bipedal locomotion: we are the only mammal on the planet that typically walks on two legs. And we’ve been doing this for a long time. Based on the fossils we have, we can say that walking upright was one of the first adaptations that made us human.

TO. You focused on the morphology of the feet. Is this the key to understanding bipedal walking?

R. Partially yes. I find the feet fascinating because each foot is made up of 26 individual bones, for a total of 52 bones. This is a quarter of the bones that make up our skeleton. These parts interact with each other to form a structure that is rigid enough to push the body off the ground, but flexible enough to absorb the force. Bipedal walking is a great opportunity to raise questions about our origins and our evolution.

Bipedality makes us human because that was the starting point.

TO. Why do you claim that walking upright made us human?

R. Walking on two legs laid the foundation for everything that happened later in our evolutionary history: enlarging the brain, freeing up the hands to make tools, changes in the torso and waist that led to finely controlled breathing that allowed us to speak and create language. . All of these things that we celebrate and know are unique to humans would not have happened if not for this unusual form of movement. Walking upright makes us human because it was the starting point.

TO. Why is upright walking so unusual among mammals?

R. Because it makes you slow and vulnerable to predators.

TO. This is an evolutionary flaw. How did he manage to thrive?

R. We don’t know. There are many things about the evolution of bipedalism that we are still trying to figure out. We’ll need more fossils to really understand this and answer this question. However, one of my favorite things we have discovered in the fossil record of our ancestors is evidence of trauma to the feet and legs. Persons who have broken their ankles or hips and this did not result in death. Quite the opposite: they were healed and survived.

TO. Where is the advantage?

R. The fact that walking upright makes us so vulnerable, and that we have evidence of people who survived some of these injuries, is a good sign that this way of walking also coincided with social evolution. Let me explain: Millions of years ago, if you broke your ankle, you couldn’t walk and you were more likely to die, but someone took care of these injured people so they would survive. This is one of the first signs of compassion and empathy for others, which eventually became one of our basic social characteristics. The fact that we care for each other when we are hurt may also have been born out of the vulnerability that walking upright brings. Caring, empathy, and compassion are evolutionary advantages that compensate for the physical disadvantages of walking upright.

TO. Walking upright caused many changes in the anatomy and behavior of our ancestors, which of them do you think were the most decisive?

R. The first hominids to walk on two legs lived in Africa seven million years ago. Their behavior is very similar to that of monkeys. When we reach Australopithecusgroup that Lucy became famous, upright walking became established as a common form of locomotion. It is no coincidence that during this time their brains increased by 20% compared to the brains of chimpanzees.

TO. So did walking on two legs help our brains get bigger over time?

R. Brains are very expensive to cultivate energetically. So where does this energy come from that increased its size? Walking on two legs is actually a very efficient form of locomotion. We don’t use much energy, and the rest can go to other tissues in the body, including the brain, which eventually increases in size. The system was then optimized. in the genre homo a more efficient form of upright walking was developed. Changes to the feet and legs allowed them to explore more territory and find more food. Eventually, thanks to walking on two legs, we spread so far that we became a global lineage.

TO. He mentioned Lucy and this month marks the 50th anniversary of its discovery, has the discovery of this australopithecus changed our understanding of early hominin locomotion?

R. Yes, absolutely. Lucy This was very important and continues to be so for science. She was the missing piece of evidence to support the hypothesis that upright posture precedes significant brain enlargement. WITH Lucy You have an ape with a relatively small brain, but with a pelvis, knees, ankles and lower back that have the characteristics of a person who can walk on two legs.

We are constantly looking for a magic pill that will give us health and longevity. We’ve got it: take a walk every day

TO. Modern man inherits design a body that began when we had a completely different way of life. What role does walking play in a world where there are cars, bicycles, escalators and elevators?

R. There is very strong evidence that walking is still incredibly good for us. We humans are constantly looking for the magic pill that will give us health and longevity. We do it this way: take a walk every day. It’s that simple. Walking reduces the risk of heart disease, stroke and diabetes. Walking is good for brain health, memory and creativity. It also protects against certain types of cancer.

TO. We should walk more.

R. I recommend that if you are physically able to take the stairs rather than take the elevator, do so. If you have the opportunity to hold a meeting standing, try doing so instead of sitting at a table. The more we can move our bodies, the healthier we will be. Think of it this way: in our beginnings, if you wanted to get food, you had to go out and look for it, walk through the environment. There are groups in Tanzania, South America and Southeast Asia that are still hunter-gatherers today. Often these populations do not suffer from some of the diseases we call modern diseases. What has happened in our current lifestyle is that we have stopped walking. From a health perspective, I think the effects are very noticeable.

TO. Are there any aspects of the development of bipedal locomotion that are still a mystery or debated in the scientific community?

R. Yes, the most important questions remain unanswered. The main one is why and how it started. What actually allowed our ancestors to move around this way without being eaten by predators in their habitat? This is something we are still trying to figure out. We also want to know what benefits it brought. Some scientists argue that one of the main benefits, besides the empathy I already mentioned, is sharing food. When walking bipedally, the hands were free, which made it possible to collect more food and give it to others. This exchange would make the population healthier. But these are just hypotheses, we are still trying to solve these questions.