It was great to talk with Jeremy DeSilva on human evolution. I enjoyed reading his book First Steps: Why Upright Walking Made Us Human. Every page was a revelation. Are you imagining our hominin ancestors hunting? I did. But not so much. DeSilva says they were hunted. Let's have another look at the Taung childs skull as modern paleoanthropologists do. This is one of paleontologys most renowned fossils. It contains the remains of Australopithecus Africanus child, which was discovered in 1924. DeSilva says that the eye sockets of the Taung child showed talon marks after a reanalysis. DeSilva says that the Taung child was probably taken from the ground by a bird of prey. It was fun!DeSilvas' book and interview might be summarized as: Everything I thought about why humans stand upright is wrong. DeSilva is a Dartmouth College paleoanthropologist. I shared with him that I was moved by DeSilva's admission in First Steps, that my scanner, camera, and calipers remained idle for the first few minutes after each visit with a new fossil. He smiled. He said that he loves fossils. I consider each fossil as an individual when I sit down with them for the first time. When I first sit down with a group of fossils, I think, Hey, in a million years, if I'm lucky enough to be one, I hope that some paleontologist will take a moment and think about me as an individual. They can then use all the scientific information they have to extract information from my bones to tell my story.I started our interview by asking him about the misconceptions that still linger in his specialty and field.OSTRICH POWER: The human feet are a problem for bipedal locomotion. There are too many delicate moving parts. Jeremy DeSilva holds an ostrich foot. The ostrich took a quarter of billion years to learn bipedal locomotion, unlike the Johnny-comes-lately Homo sapiens. You get a foot that engineers would argue is much better for locomotion.What are the most common scientific errors in explaining why people stand upright?We can always change our minds as new evidence becomes available, right? One wrong idea is still with us. 2001: A Space Odysseyis based on the belief that we were a violent species and developed bipedalism to make it easier for us to use our weapons. This was based on misinterpretation fossils found at Makapansgat, South Africa. Australopithecus allegedly killed the bones. It turned out that they were hyena remains. Another popular belief is that bipedalism evolved to allow us to see through tall grass. It's true that if you look over tall grass and see predators, the best thing to do is run away with two legs. You were too slow. It would be logical to run on your hind legs, but you can gallop at twice as fast as a normal human.Even Usain Bolt would be toast.Yes. He would. Even Usain Bolt, the fastest human being we can imagine and probably the fastest person to have ever lived, is still pathetically slow when compared with a quadrupedal creature on an African savanna. Usain Bolt can travel approximately 28 miles per hour. This is half the speed of an antelope, leopard, lion or galloping zebra.This is not the story behind the T-shirt image of a chimpanzee becoming a human.Your research has shown me that we did not evolve from hominins who walked on all fours. Our evolution came from those who were able to walk upright.This topic is very hot in our field and there is much disagreement. We will see if we find more fossils. My interpretation of the time period when bipedalism emerged is that apes don't move on their knuckles. They are not well-adapted to life on the ground. They prefer to be high up in trees and use hand-assisted walking, just like gibbon, siamang, orangutans. We refer to them as lesser apes because they move bipedally quite a bit. It is interesting to note that chimpanzees, gorillas, and knuckle-walkers don't move bipedally as often.There are fossils from Southern Europe that show that apes have a slightly upright body position. It is possible that knuckle walking might be the most recent form of locomotion. This is not how the chimpanzee image we see on bumper stickers, coffee cups, and T-shirts might have turned out. It is possible that the common ancestor was taller and that chimpanzees were able to walk independently.This famous image is known as March of Progress. Let us know your thoughts.March of Progress was an illustration by Rudolph Zallinger (a Russian artist) in 1965 Time-Life called Early Man. This beautiful foldout shows ancient apes on all fours and they slowly rise up to meet modern humans. With the fossils available at the time, it was possible to create a story like this. We have made many incredible discoveries over the past half century that prove the human family tree is more diverse. It is interesting to see that evolutionary change happens at a different pace. In fact, upright walking was the first evolutionary step. Bipeds first appeared on the ground from upright trees. All that really happened was ecological change. These hominins lived in an environment with fewer trees. You already have the ability to stand upright and move on two legs to get you from A to B in order to continue your journey. Bipedalism would not be a new form of locomotion in that situation. It would be an old method of moving. It was only in a new environment on the ground than in trees.Uncle Leo / ShutterstockBipedalism is slow and easy prey. Why didn't our ancestors die? Why are we here?This is a very important question. Are there any advantages to letting go of your hands? You could also carry babies and food. Thermo-regulatory adaptations are also available. You can better disperse heat by being on two legs instead of four. Those things may have been factors that enabled us to survive.What is the most adaptive trait that early hominins have to be able to stand upright?I don't know. Any characterization that stated there was only one reason would be wrong. We would know if there was a reason. It would be obvious. Bipedalism could have evolved independently from other hominins in Africa. There is a chance that bipedalism didn't happen just once, based on the fossils available. We know that evolutionary trends are a constant process. Good ideas can evolve over time. The evolution of feathers, dinosaurs, and other species has happened three times independently. Multiple independent evolutions of bipedalism could be possible.Is it not a misnomer to believe that only one hominin exists at any given time?It is. It is. One of the many things we learned from fossil discoveries was that there appear to have been different species of early humans, or hominins, living on the same landscape. They may have had different anatomies and adaptations in their feet or legs. They would have walked differently. Lucys species Australopithecus Afarensis is a classic example. It lived approximately 3.5 million years ago and covered the entire continent from Ethiopia to Tanzania.Yohannes Haile Selassie, a colleague of mys, found a foot skeleton in Ethiopia a few years back. It was in sediments that were the same age as Lucy. It was expected that it would be a foot like Lucy's species. However, Lucy's species did not have a big grasping toe. This one does. Other bony parts are consistent with the ability to push off the ground with two legs. This is how we see something that walks on two legs but uses two legs differently to Lucy and her type.My students tell me all the time how much fun it would have to travel back in time to Africa three or four million years ago. All these hominins would be coexisting in a landscape eating slightly different foods and moving in slightly different ways.Usain Bolt can travel at 28 miles per hour. This is half the speed of a leopard, lion or zebra.It is clear that Lucy's life would have been difficult. You are right.You are the slowest living thing in your environment. You are small. Lucy, an adult Australopithecus, was three-and-a-half feet tall. She couldn't have been any taller. Her wisdom teeth have erupted, and her growth plates are fused. She shares the scene with a Homotherium, which is a large saber-tooth cat. They were the ancestors and giants of hyenas. Some of them were the ancestors leopards and lions. These animals would happily eat an Australopithecus. We actually have fossils that show puncture marks on the back of their heads. They were eaten.Lucy would have woken in a tree. This is how you avoid getting eaten at night. As large cats finished their dinners that night, she would have needed to hold on tight. She would have been hungry. Her group would need to descend from the trees in order to eat. You can't put a baby on your head if you are a biped. You're going to fall off the baby.Baboons and baby chimpanzees hold on to their mothers' backs or fronts. To be upright, we must physically carry our children. Lucy now physically carries her child. She now has a little meal for a carnivore in her arms and must go out to find food in a predatory environment. Yet, she survived! Amazing testament to the strength of our ancestors. Their survival is the reason we are here.What were the key characteristics of Lucy's survival?You share food if you live in a group that is cooperative, like early hominins. It is shared with your family, to your children and to other members of the group who in turn reciprocate. This builds trust and fosters a culture of cooperation that is vital for survival. I believe that hominins would have survived millions of years living in an environment full of predators if they were more cooperative and looked after one another.GregGrabowski/ShutterstockHow does paleoanthropologists know that early hominins were cooperative in their behavior?A fossil of a person who has broken a leg bone (a femur) is one of the most important pieces of evidence that we have. This was long before doctors, casts and hospitals. You can see a healed fracture in the fossil. Imagine that you have broken your leg 2 million years ago. It's impossible to survive. A hominin survived. He was healed. He was able to overcome that trauma. He could not have done it alone, I think.Was bipedalism the catalyst for cooperation?Yes, I believe so. Humans are thought to have evolved from chimpanzees, which can make them extremely aggressive and violent. We are also related to bonobos who aren't aggressive nor violent. They are female-dominated and don't display the same territorial behavior as chimpanzees. We didn't evolve from either one of these. They are our cousins. They share a common ancestor. They are a fascinating mirror that allows us to reflect on ourselves and the common ancestor.We all know how cruel people can be to one another. This is well-known. We forget to recognize that humans are extremely cooperative, kind, helpful, compassionate, and tolerant of one another. I believe that what made an ape survive millions of years in a harsh environment without weapons was the fact that they looked after one another, and took care of each others. We looked after each other. We helped someone injured to climb a tree.Perhaps it is better to say that cooperation is a side effect of being vulnerable bipeds.This is exactly right. Apes that aren't bipedal and can't move in trees are destined for extinction. We are here. We were able to overcome the rigors natural selection. It also cooperated. Childbirth is one of the most prominent examples. Childbirth is quite easy in non-human primates. When the baby is born, it will usually face forward toward its mother's belly. Because of the pelvic changes associated with walking on two feet, babies in humans are forced to twist through the birth canal. As a result, they often have to be born facing the back. This is because it requires assistance. Humans have a cultural universal that requires assistance during birth. This is usually provided by an experienced midwife. Trusting another member of your family during childbirth is a sign that you will trust them later.When someone asks about the Paleo diet I will answer, "Which human population are you referring to?"What is the secret to brain development through bipedalism?These are more speculation. We weren't sure. Darwin proposed that bipedalism, tool use, canine reduction and brain growth all evolve together. The March of Progress illustration illustrates Darwin's ideas. Brains are growing larger as bipedalism becomes more sophisticated. However, this is not the case. We find that bipedalism is rooted in the roots of the lineage. The brain size does not increase until much later. Around 2 million years ago, brain size began to increase. Australopithecus brains grow a bit more than their predecessors but not as much as what we see with genus homo. This is because the brain, an energetically expensive organ, has enough energy to grow.It's a zero-sum game when it comes to energy, right? The body has a limit on the amount of energy it can use and allocates it to the most important organs.It's true. That's right. The digestive system is at the heart of this argument. The intestines shrink in volume and you can allocate more energy to a bigger brain by decreasing the cost of tissue. You can't digest plants as well if you don't cook them. There seems to be a relationship between diversifying our diet, eating meat and marrow more, scavenging and hunting. Fire is also important, as you can now cook. All of these things fuel brain growth.Bipedalism: Where is it?This is also reflected in an increase in leg size. The arch of the foot becomes more human-like. These final adjustments make bipedalism more efficient and allow us to travel further, expanding our home range. We can now extract more resources from the environment by expanding our home range. You can now eat both animals and plants in a wider area.Also in Paleontology: The Day the Mesozoic died By Sean B. Carroll. Understanding how to decipher historical events written in the book rocks may be as fascinating as the event itself.Is bipedalism a contributing factor to humans becoming omnivores, or is it?It did, I believe. It is possible to see the isotope signatures of teeth from our earliest ancestors and determine that they were eating in a forest environment. They were eating leaves and fruits, which is what an ape would eat. The profile of the isotopes changes dramatically when Lucy arrives in Australopithecus. They also show that Lucy began eating many different foods in different environments. This is consistent with the fact that a biped spends more time on the ground to get their food than they do in trees.Lucy's life was difficult. She cannot afford to be picky. She won't search endlessly for the one thing she is craving. Predators are everywhere. Shell will be eaten, and her child will also be eaten. She had to eat everything. She had to eat leaves, grasses, and fruits. She might find a carcass that has some meat on it and could eat that. She could also dig underground tubers to eat them. She would eat insects, termites, birds and eggs as well as eggs, lizards and snails. Humans do the same thing today.That seems to me to be the end of trendy diets that suggest we should eat a particular food type because that is what our ancestors ate.[Laughs]. When someone asks me about Paleo, I'll answer, "Which population?" You are referring to humans living in Northern Asia, Europe, Africa, or humans living in forested regions. Humans are unbelievably flexible when it comes to diet. You can eat almost anything. We could eat anything in these diverse habitats. Humans don't have a single diet that works for everyone.We are now in 2021 and live in a completely different world than our hominin ancestors. How can bipedalism be not adapted for modern life?A few weeks ago, I couldn't walk because my back was hurt. Our lower back is in a state of disarray. Mammals move on their hind legs, and the spine of mammals is horizontal. It acts like a suspension bridge. Bipedals have made the spine vertical. To ensure that our torso is aligned over the hips and all of our joints are balanced and aligned, a curve has been introduced to the spine. Bruce Latimer, a Case Western Reserve University colleague, calls this a series "cups and saucers". This is how unstable the spine can be. Slip discs are quite common. Were one of few mammals to develop scoliosis.The foot is the worst part. Engineers would be unable to design a structure that can absorb ground forces, yet rigid enough to push off ground and elastic enough to absorb energy. Your foot is made up of 26 bones. You have 52 bones between your feet. This is about 25% of your total skeleton. Foot bones make up a quarter of the human body's skeleton. Why is this? This is because they are modified apes and have all the foot bones needed to grab onto trees. They use their feet much like our hands. Natural selection cannot work with pre-existing forms of bipedalism. It experimented with the ape foot. It was like using paper clips and duct tape to fix up and stiffen this foot. It's good enough. We are here, and we can get from A to B. Evolution doesn't care about comfort and we have many problems.Are there more messages about evolutionary biology than our anatomical problems?Yes. It's back to what we talked about earlier. Culture helps humans to buffer themselves. Are humans still subject to natural selection? Yes. For the past 6 million years. It may not be optimal and cause problems. We solve our problems socially and culturally. We are not waiting for natural selection or twiddling our fingers to solve them.Kevin Berger is Nautilus' editor.Image by Roni Setiawan/Shutterstock
