WHY EVOLUTION’S DESIGN ENDURES

Evolution has hard-wired health to happiness, which means happiness is not as hard to assess as we make it out to be—not if you approach it from the wild side. Ultimately, we don’t need someone else (or a book, for that matter) to define our happiness. Our brains do that. Every single aspect of the way we are wired and evolved makes it our brain’s job to tell us if we are okay. Our survival depends on it being so.

Think of what our lives would be like if this were not true, if the body operated on perverse feedback loops that would tell us we are okay when we are, in biological terms, doing badly: we are hungry, cold, exhausted, and broken, and the brain says we are fine. Imagine such a feedback system, and then imagine the prospects of survival for an animal that has it. Imagine it being encoded and passed on in genes. But no need to imagine. This is precisely the perverse system that prevails in a drug addict, a hijacked system that says he is doing well when everybody can see he is not. Survival prospects? We know this answer without further study.

What we need most to understand from this is that our happiness is greatly dependent on our biological well-being, and the conditions of that well-being have been laid down by the imperatives of survival, by evolution.

All of this means we need to pay attention to the conditions of human evolution to ensure our happiness. But the problem is, we don’t. The popular understanding of human evolution is more or less wrong. But more important, the way we live is a clear and long-standing set of violations of the rules of human well-being, and it’s making us sick.

First, summon that image that invariably pops into mind when we begin to think about human evolution: the series of cartoon panels in progression—first ape, then caveman, then us, and then a punch line. These ubiquitous cartoons make great jokes, but the idea behind them is wrong in an important way. So is the concept of a “missing link.” The cartoon supports the idea that evolution gradually produced modifications and changes in human design in one neat, clear progression from our ape ancestors to who we are today, that the change was progressive, and that the process continues. All of this is wrong.

Since the time of Darwin, there has been a running debate among evolutionists, with Darwin himself taking the view that evolution was and is built on gradual transition, shade to new shade, almost imperceptibly between generations. The opposing and minority view through most of this debate has been that evolution makes sudden radical shifts, a view the controversial evolutionary biologists Stephen Jay Gould and Niles Eldredge labeled “punctuated equilibrium.” The consensus now in human evolution is with the latter point—punctuated equilibrium—and we agree.

In fact, the consensus view says the package we call human, Homo sapiens, emerged as a whole in Africa on the order of about fifty thousand years ago. Not much has happened since. This is Human 1.0 and there have been no significant upgrades.

The consensus view was laid out by Gould himself: “There’s been no biological change in humans in 40,000 or 50,000 years. Everything we call culture and civilization we’ve built with the same body and brain.”

Yet embedded in this same cartoon and in popular understanding is a second, wrong idea, the idea of a series of links and missing links. In fact, there was not a neat line of human ancestors, each shading to the next to become more and more humanlike every step of the way. The human family tree is not a towering pine with a dominant central trunk. It is more of a bush than a tree, with a series of side branches and dead ends. The most obvious example of this is the case of the Neanderthal, long known from the fossil record in Europe, Asia, and North Africa. Neanderthals are the knuckle draggers in the middle panels of the cartoon; they’re also a term of insult that we use for fellow humans we consider unrefined or “unevolved,” to cite one of the more egregious readings of the fundamentals of evolution. The assumption in this is clear. Neanderthals were simply a step along the way to the pinnacle, to us.

But human evolution is not a linear progression. Rather, there evolved and existed for literally millions of years—much longer than we have existed—a handful of species of viable, big-brained, upright, tool-wielding, hunting, social primates, each successful in its own niche and place. Yet modern Homo sapiens appear on the scene only fifty thousand or so years ago, after 90 percent of hominid evolutionary time has already passed, and suddenly we become a breakout species. Suddenly, all of those other perfectly viable hominid species are extinct, every single one. We are the only remaining species in the genus Homo.

Interestingly enough, there was a corresponding decrease not just in species but in genetic diversity among Homo sapiens. All species of Homo, not just Homo sapiens, trace their lineage to Africa. There is no serious debate or disagreement about this. And there remains in Africa some genetic diversity among Homo sapiens, just as one might expect in a center of origin. But beyond Africa, there is very little genetic variation in humans. There’s a good explanation for this. Separation of populations is the sponsor of diversity and speciation. That is, branches occur in an evolutionary tree when some sort of usual natural event—sea level rise makes an island; glaciers divide a home range—isolates subpopulations and they begin to diverge genetically. But for at least fifty thousand years, all humans have been connected to one another through travel, trade networks, and migration. The result is a genetically homogeneous population. As a practical matter, this means when we speak of human nature, we speak of all humans, both through the time span of fifty thousand years and across the planet. Our long-standing networks of connection mean there is no pressure to drift toward a new species, no pressure to evolve.

Nonetheless, there is some variation and even innovation. Much is made of these differences among populations for deep-seated reasons having nothing to do with genetics. Take, for instance, the relatively recent experiment in light skin and blond hair. Through most of human history, maybe 80 percent of it, humans were universally dark-skinned. The experiment in light skin began in Europe only about twenty thousand years ago, an adaptation to inhabiting places with little sun. Think of how much we humans make of this tiny and insignificant blip in the total genetic makeup of our species, how much of recent human history hinges on who has it and who doesn’t, “it” being a subtle little tweak not even readable in the collective genome.

Other recent experiments include such genetic variations as lactose tolerance and resistance to malaria as evidenced in a tropical disposition toward sickle-cell anemia. In this sense, we humans are evolving, but over the course of fifty thousand years, the changes have been so slight as to border on inconsequential. At least by genetic predisposition, we are no taller, no faster or slower, no smarter than were the first Homo sapiens. We are to the core the same guys who somehow outcompeted, outsurvived a handful of very similar upright apes to do something no other species has done before or since: inhabit every square inch of land on our planet.

But no matter how it happened, it is clear that something unprecedented took place about fifty thousand years ago. This creature called “human” appeared all of a sudden and almost as suddenly was a breakout species. The evolutionary changes that powered this breakout are the core strengths of our species and the very characteristics that we ought to pay attention to. What are these traits?

BORN TO RUN?

Start with bipedalism and running. Our habit of walking on two legs is instructive in terms of what we might gain by reexamining the issue with a fresh set of eyes.

There’s a beat-up pair of Inov-8 running shoes parked under David Carrier’s desk in his office at the University of Utah, and the trained eye can spot these as every bit as telling as the shape of a thigh bone. This brand is British and happens to be favored by a subset of the tribe of minimalist runners who negotiate rough mountain trails. Carrier, a trim, genial middle-aged guy with oval metal-rimmed glasses, a brush of a mustache, and a frizz of curly hair, confirms for a visitor that he is indeed a mountain runner, but this is not his claim to fame, at least in the running world, and his claim to fame in the scientific world is different still. Runners know him as the guy who tried and failed to run an antelope to death in Wyoming but then eventually figured out how to get the job done with instruction from African bushmen. Turns out it wasn’t about running; it was about empathy.

Carrier’s work and that of his colleagues—his mentor Dennis Bramble, also of the University of Utah, and Daniel Lieberman of Harvard—is significant beyond dead antelope to those of us who run and those of us who should run. Their findings figure front and center in a way-too-common experience: a runner consults a doctor to complain of some injury and then hears the doctor intone the sober advice, “You know, the human body is just not made for running.” Thanks to Carrier’s work, the runner can confidently answer, “Nonsense.” Humans are in fact the best endurance runners on the planet. The best. Might this have something to do with our dominance of the planet, that we are the lone surviving upright ape?

Much is made of the fact that apes are our closest relatives, that humans are the third species of chimpanzee, and this has produced the related and wrong assumption that humans are simply apes with somehow more refined apelike features, a tweak here, a tweak there—new shades, not new colors. Yet the evidence from endurance running makes a very different case. Humans are a radical departure from chimp design.

In their pivotal paper about this in the journal Nature, Bramble and Lieberman analyzed the whole issue in terms of running versus walking—a way of challenging the common assumption that humans are built to walk, not run. All apes can run, sort of, but not fast and not far, and certainly not gracefully. Humans can do all of this, and this simple fact can be clearly read in our anatomical structure, in the bones. The research detailed twenty-six adaptations of the human skeleton specific to running, not walking. Some of these are, as you might expect, in the legs and feet. For instance, running requires a springy arched foot, which humans have but no other apes do. Likewise mandatory are our elongated Achilles tendons and long legs relative to the rest of the body. Running, as opposed to walking, requires counterrotation, which is to say that the upper body rotates counter to the lower, negotiated by a pivot of the hips. So running requires a far greater commitment from the upper body than walking does, and a whole collection of features designed to cope with the shifting mass.

All of these features we share with other running species, even though all of the others are quadrupeds like horses and dogs (and the fact that these two elegant runners are our closest domesticated companions through time ought to serve as a hint to the basis of the relationship). We share none of these characteristics with other species of apes—that is, with the species one limb away on the family tree. To adapt humans to running, evolution reused some older adaptations from unrelated species, and all of this took place suddenly about two million years ago with the emergence of our genus, hominids.

This means that not only are we adapted to run, but running defines us.

Science has known some of this for a long time, but it was Carrier who demonstrated why this sudden departure from the rest of the ape line was so important. His working hypothesis was something called persistence hunting. True enough, many mammals, especially mammals long recognized as important food sources for humans, are terribly fast runners. Evolution takes care of them as well. But those creatures—usually ungulates like deer and antelope—are sprinters, meaning all flash but no endurance. Carrier believed that if running was so important as to deliver a watershed in evolution, humans must have used the skill to get food, persistently running game animals until they tired and faltered, and then closing in for the kill.

He gave this a try in Wyoming, where there are plenty of antelope. He found he could indeed single out an animal from the herd and track it and chase it long distances, but just as the chosen animal was beginning to tire, it would circle back to the herd and get lost in the crowd, and Carrier would be stuck on the trail of a fresh animal ready to run. Finally, though (and by chance), Carrier learned of tribesmen in South Africa who still practiced this form of hunting. He went to Africa and learned the trick, and it did indeed involve endurance running, but it also involved a sublime knowledge of the prey species and its habits, a knowledge bordering on a supernatural ability to predict what the animal would do. The running itself was meaningless without a big brain. This connection is a track worth following, but the success of the bushmen in Africa at least allowed Carrier, Bramble, and Lieberman to close their case. Humans are indeed Born to Run, to cite the title of Christopher McDougall’s popular book, which summarized their work.

End of the trail? Not really. In our conversation, Carrier mentioned almost none of this, and in fact took issue with some work by Bramble and Lieberman that says the human gluteus maximus buttresses the case that we are born to run. He says that the muscle in question, the butt muscle, plays almost no role in running but does show up in a host of other activities, and it is those other activities that have his attention now. He launches into a line of thought drawn from a concept pivotal in the original research—an enigma, really: a notion called cost of transport.

It’s a relatively simple concept that gets straight at the efficiency of locomotion. Imagine a graph, with one axis showing speed and the other axis graphing energy expended by the creature in motion. For most species this graph forms a U-shaped curve, and the bottom of the U is a sweet spot. At this speed, the animal in question covers the most distance with the least energy, just as a car might get its best gas mileage at, say, fifty-five miles per hour. It marks the point of maximum efficiency, the best speed in terms of units of energy expended. The very existence of the U shape says that most animals have bodies meant for a given speed, a point where energy use is minimized.

Humans match the rule, but only when walking. That is, human walkers lay out a curve with maximum energy efficiency of about 1.3 meters per second. That speed uses the least amount of energy to cover a given distance. But running, at least for humans, does not produce a similar curve with a defined sweet spot; it yields a flat one. We have no optimum speed in terms of energy spent. Meanwhile, all other running animals—horses, dogs, deer—do produce a U-shaped curve when running.

So if humans are born to run, where’s the sweet spot? Evolution likes nothing so much as energy efficiency. Species live and die on this issue alone, so why isn’t human running tuned for maximum efficiency?

Further, the whole question offers a parallel line of inquiry, not among species but within the human body itself. That’s where Carrier is headed with this, but he first notes that the flat cost-of-transport curve for human running appears only when you summarize data for a number of humans. On the other hand, looking at data for each individual does indeed produce a U-shaped curve, but the sweet spot is in a different place for each human. That’s not true for other species, so right off, this suggests that there is far more variability in humans, and it has much to do with individual conditioning and experience.

But more interestingly, this whole line of reasoning can be and has been examined not just between species and among individual humans but among individual muscles within a given body. Muscle recruitment and efficiency vary according to activity, even with running. Running uphill requires one set of muscles, downhill another, on the flat or side hilling different ones still. So does running fast or running slow. But further still, so does jumping. And throwing, pushing, punching, lifting, and pressing.

Carrier says that the research on this shows no favoritism, no sweet spot according to any one activity, no real specialization, and this result is counter to what’s found with any other species. For other species, one can make a categorical statement like “born to gallop,” but for humans, no. Born to run? Yes indeed, but also born for doing other activities as well. Humans are the Swiss Army knives of motion.

“This is not a surprise to the vast majority of people who think about what humans do, but I think it is a surprise to the folks who are so focused on the running hypothesis. We are an animal that needs to do a variety of things with our locomotive system,” Carrier says. “We do more than just walk economically and run long distances.”

All of this movement dictates a couple of fundamental conditions of our existence: we need to take on enough nutrients (not just energy but nutrients) to power all of this motion, and we need outsize brains to control diverse types of locomotion. Thinking, creating, scheming, mating, coordinating—all those activities also require big brains, but locomotion alone is enough to seal the deal. The evolution of our unique brains was locked into the evolution of our wide range of movement. Mental and physical agility run on the same track.

FUEL

There is a paradox at the center of human nutrition. All the other parts of our body seem very good at what they do, are standouts in the animal kingdom, but we are truly lousy at digestion, which is limited and puny. Literally so, because we have to be lousy at it. First off, digestion is an energetically demanding process, so why burn the calories just to take on calories if there is a better solution? But second, if we are going to be able to move around rapidly upright, we need small guts, and small guts mean short intestines, less real estate for digestion. This bit of elemental engineering is a consequence of a number of design features, but the counterrotation we talked about with running is a good case in point. Unlike all the other apes, which are quadrupeds, we have a significant vertical gap between the bottom of our ribs and the top of our pelvis, the territory of the abdominal muscles. These muscles effect the leverage necessary to keep us reliably upright and control the twist of running, so we need a light, tight abdomen, or tight abs, which restricts room for intestines.

This anatomical adjustment explains much in human makeup and behavior, but start with a simple and profound fact: our short guts mean we can’t eat grass, and this is no small thing, especially if you consider that two million years of evolutionary history occurred in savannas and grasslands. Grasslands are enormously productive in biological terms; that is, they efficiently convert solar energy into carbohydrates. But that energy is wrapped in the building block of all grasses, cellulose, and humans cannot digest it, not at all.

Our primary method for overcoming our inability to digest is to outsource the job. Our prey animals, the ungulates—grazers and browsers, largely—happen to be very good at digesting cellulose. These quadrupeds can handle such tasks as chewing cuds, patiently feeding and refeeding wads and tangles of grass into a labyrinth of intestines contained in a monumental bulge of a gut.

There is no ambiguity in the fossil record, in paleoanthropology or anthropology, in everything we know about the human condition, past and present.

Humans are hunters and meat eaters. There is no such thing as a vegetarian society in all the record. Eating meat is a fundamental and defining fact of the human condition, at the gut level and bred in the bones.

Discussion about this has generally been cast in terms of protein. Essential amino acids—proteins—are necessary building blocks for that highly adapted body. The only complete source of those amino acids is meat. True as that may be, it misses some essential points, as have anthropologists and nutritionists in trying to do the calculations that explain our continued existence. When we think of meat today, we think of, well, meat, defined as muscle tissue. We disregard the rest, all those other tissues of the animal body. It’s not a new mistake.

In the nineteenth century, when Europeans were exploring North America, a few explorers and fur trappers made contact with the nomadic Indians of the northern plains, a people who, like many hunter-gatherers, lived almost exclusively off animals. The Europeans of necessity adopted that diet and soon found themselves quite ill, even to the point of sprouting open, running sores on their faces. They were like we are today and ate only muscle meat. But then the Indians showed them the choice parts, the bits of liver and spleen, bone marrow and brain and the fat, especially the fat. The Europeans ate as they were told and got better because the organ tissue contained some essential micronutrients lacking in the muscle meat.

The basic energetics of an animal diet involve not just protein but also and especially fat and micronutrients and minerals, a matter of bioaccumulation. Grazers store excess energy as fat, in and of itself a dense, rich source of calories to fuel our demanding bodies; but in doing so, they bioaccumulate a rich storehouse of elements like magnesium, iron, and iodine that the deep roots of grass pull from mineral soil. This is also an important factor. Certainly we could (and do) get many of these by eating plants directly, but they are far more concentrated in meat. To get everything we need from plants, we would have to eat far more than we literally have the stomach for. Further, these minerals and micronutrients tend to be unevenly distributed on the face of the planet, as any miner for magnesium, iron, or iodine will tell you. But the big grazers tend to be migratory and range over vast areas, thereby averaging out conditions and balancing geology’s uneven hand. Over time, grazing animals accumulate a full range of nutrients as no stationary plant can, and we take advantage of that life history as stored and accumulated in an animal’s body.

Yet our need for variety and diversity in diet also shows up in our omnivorous habit. Humans have for all human time eaten a wide array of plants and wandered far and wide to gather them, and this, too, is more than a simple matter of energetics. Diversity ensures the range of micronutrients to support the complexity of the human body, the importance of which will emerge in detail as we develop this story. All of this gets greatly aided by our cultural adaption involving the use of fire, which allows cooking and so further aids in concentration and digestion. Add to this our microbiomes, which are another way of outsourcing to compensate for our poor digestive abilities. Our guts are loaded with thousands of species of bacteria that break down food and add value—a lot more than we think.

By and large, though, these patterns—nomadism, bipedalism, and omnivory—are defining for our entire genus and have accrued over the course of two million years of hominid history. Yet there is a variation in this theme that illustrates its refinement and gets to our more central question: the difference between Homo sapiens and all other hominids, now extinct. The general approach to food outlined here is true of all the species of hominids, even Neanderthals; yet recall that our basic question is why the single species of humans, modern humans, beat out people like the Neanderthals.

Neanderthals were indeed hunters—in fact, highly skilled hunters—and, if anything, they were more selective to very large prey animals than Homo sapiens were, meaning that Neanderthals had the skills and social organization necessary to kill elephants with spears. They had big hunks of protein and fat, the very thing that gave all hominids the edge. Neanderthals had bodies that were as upright and graceful as ours. They had plenty big brains. What they did not have, compared with the Homo sapiens of their day, was fish. More to the point, they had not learned how to tap this source of nutrition that was all around them.

Their chief competitors, Homo sapiens, had. Evidence of fishing first appears in Africa, but only in Homo sapiens. When our species showed up in Europe and Asia about forty thousand years ago, fishing of marine and freshwater sources was widespread and important on both continents.

This is not to argue that fish gave Homo sapiens the edge that wiped out Neanderthals, Denisovans, and Homo floresiensis, the other hominid species already in Asia and Europe then—although it’s possible. But it does signal something important to modern nutrition, especially in the case of salmon. Remember: we can prove that those ancient Homo sapiens ate fish because of chemical signatures, which is to say that some elements not present in terrestrial species were present in fish, and those elements accumulate in human bones, the fossil record. Further, anyone who has ever witnessed a salmon migration, even in today’s relatively impoverished conditions, understands that collecting this protein took almost no effort, as it was an almost unimaginable abundance. Forget persistence hunting: salmon eaters need only sit at streamside and rake it in, literally tons of high-quality protein. But each of those salmon, one of the world’s most peripatetic species, has ranged thousands on thousands of miles across diverse marine and aquatic environments during its short life cycle. That is, each fish has sampled and bioaccumulated a diverse collection of micronutrients lacking in a terrestrial diet. Remember the value of diversity realized by nomads hunting across diverse environments. Nomads eating a nomadic marine species takes that idea up a notch: nomadism squared.

EMPATHY

The message here is diversity, and we will hear it again. But this is a small element of the larger success of humans. The details remain somewhat in dispute, but from such evidence paleoanthropologists have through the years assembled a list of traits they believe defined us as humans. In a recent book, the British scholar of humanity’s roots Chris Stringer offered one such list, as good as any:

Complex tools, the styles of which may change rapidly through time and space; formal artifacts shaped from bone, ivory, antler, shell, and similar materials; art, including abstract and figurative symbols; structures such as tents or huts for living or working that are organized for different activities (such as toolmaking, food preparation, sleeping, and for hearths); long-distance transport of valued materials such as stone, shells, beads, amber; ceremonies or rituals, which may include art, structures, or complex treatment of the dead; increased cultural “buffering” to adapt to more extreme environments such as deserts or cold steppes; greater complexity of food-gathering and food-processing procedures, such as the use of nets, traps, fishing gear, and complex cooking; and higher population densities approaching those of modern hunter-gatherers.

It is a long list that accounts for much, but its elements, the traits, are derivative. They certainly derive from how we move, our athleticism, and what we eat and how we get it. But there are activities in here that do not derive from simple biological energetics, how we translate energy into life. Symbols (and remember: words are symbols, so this includes language)? Art? Music? Ritual? Clearly this list is telling us that something important and unprecedented has happened in our brains, something well beyond bipedalism, tight guts, voracious appetites, salmon, and the big brains that were characteristic of the hominid line for the preceding two million years.

The biologically unprecedented structures in the brain that enable these abilities don’t leave much of an impression in the fossil record, so there is no hard evidence of when they appeared. We have come to know them only recently through neuroscience, an exploding field that continues almost daily with discoveries that illuminate the complexity of the brain. Yet a couple of structures, a class of cells or parts of the brain we’ve known about for some time, give us some hint as to why human abilities exploded on the scene fifty thousand years ago. For instance, since the 1920s, we’ve known about spindle neurons—a uniquely shaped set of cells that first showed up in ape brains, and to a lesser extent in dolphins, whales, and elephants, all animals known for having unique abilities. Humans have many more of them in very specific areas of the brain, and they are involved in complex reactions like trust, empathy, and guilt, but also in practical matters like planning. (You might ask why empathy and planning run together. Good question. Answer coming.)

Add to that a related and even more wondrous set of cells that neuroscientists call “mirror neurons,” first discovered in the 1980s and ’90s by a group of scientists in Italy. These get more to the point of empathy. The term “mirror” is apt. If we monitor a monkey’s brain while the monkey is eating a peanut, the readout shows a set of firing neurons associated with activities like using a hand to pick up the peanut, chewing, and registering the satisfaction delivered by the food. But if a monkey watches another monkey eat a peanut, that same set of neurons—the mirror neurons—fire in his brain, as if he himself were the one eating the peanut. This is a major part of the circuitry of empathy, which is defined as a notch up from sympathy. More than simply realizing the feelings of another, we also literally feel them ourselves.

It would be hard to overstate the importance of this in social cohesion, but a bit of reflection shows how far this extends. It gives us some sense of another person’s story, ascribing consciousness to other beings. It allows us to understand that they do not see the world as we see it, the importance of which is best understood by observing people who do not have this ability. For instance, people who have autism are notoriously altered in this very circuitry and these abilities, which is why they don’t lie. They don’t see the point of lying, because they think everyone else knows exactly what they know.

This consciousness of another’s point of view is exactly what enables the more elegant and refined form of lying so valuable to all humans: storytelling.

It allows abstraction and conceptualization, which in turn allows language. It allows a concept of the future, which in turn opens the door to planning and scheming and is why planning is related to empathy. But it also gives us a sense that others see us, and hence body adornment shows up in the archaeological record. So does art, which is an extension of adornment but also a mode of storytelling, a symbolic representation of the world external to us.

All of this, on the other hand, comes at a great cost. As we have said, the brain is a costly organ in terms of the energy required to keep it humming along. Any additions simply increase that load, but these are more than simple additions, more than a few more cells tucked away in a discrete corner. The activities associated with spindle and mirror neurons are characterized not by the firing of a few cells but by the assembly of networks of cells all firing in concert, a glow of energy humming around the entire brain. These, unlike many of our more mundane tasks, are whole-brain activities, heavy calculation loads. This load translates into a requirement for even more calories to support it.

Yet there are more than these immediate costs involved, hinted at by one of the more intriguing and sobering bits of evidence in all the vast collection of bones: the case of a single individual, D3444. We know him only by his skull, but that’s enough to tell us he was a Dmanisi man, which places his life in what is now the nation of Georgia about 1.8 million years ago. He is not even Homo sapiens; Dmanisi people were like Neanderthals, a separate species of hominids that left Africa long before Homo sapiens and eventually settled the grasslands east of what is now Europe. D3444 is a special case simply because his skull has no teeth, but, in fact, he had no teeth long before he died. Anthropologists believe this is evidence of infirmities that would have made him dependent on others for his survival. He needed help, and he got it, because hominids take care of those who can’t take care of themselves and have done so since before they were humans. This generosity has real biological costs in terms of energy spent. All of this means that empathy must confer benefits greater than those costs, or it would not still be with us. This is axiomatic in evolutionary biology.

Yet any accounting of this matter can easily miss the even larger point in play. We need not look long and far for cases of humans caring for helpless humans, and this brings us to what is perhaps the most salient point of humanity, the fundamental fact of our existence largely overlooked in these discussions, because like many fundamental, important, and profound facts of life, it hides in plain sight. We take it for granted.

The biological term that we need now to move this discussion forward is “altricial,” meaning simply “helpless young.” Of course they are. Helpless is almost the very definition of the young of any species, from baby robins to newborn, sightless puppies. But this topic teases out probably the most significant difference between our species and all other animals now or ever. Our young are more or less helpless for a very long time, longer than any other species—fourteen, fifteen years. (Some present-day parents would insist that it’s twenty-five or thirty years.) No other species is even remotely close to us in this regard. This, too, is a defining fact of the human condition.

And it is not happenstance but a predictable, derivative trait, given our big brains. Humans cannot be born with fully formed brains simply because the resulting head would not fit through the birth canal. Rather, our brains are built and formed after we are born, like a ship in a bottle, a process that takes fifteen, maybe twenty years.

Volumes of understanding and entire disciplines and sets of wisdom derive from this simple fact, but applying it to paleoanthropology offers a new lens on the human condition. In fact, some in the field now argue that this simple fact of life is the most salient characteristic of human nature, the founding fact of our life. Our young are so dependent that no parent is capable of the task of supporting and caring for that infant—not just the attention and protection, but the teaching and feeding. Hunters and gatherers must meet the energy demands of lactating mothers back in camp. Mothers simply cannot raise infants alone, and this dictates social bonding. The basic social contract has babies as its bottom line. Without this, the human species cannot go on as it is. All evolution hinges on successful reproduction of the next generation. In the case of humans, this is an enormous task. Through all human time, across all human cultures, there emerges a number associated with this task. It takes a ratio of four adults to one child to allow humans to go on. This is the real cost of our big brains.

This is why we must cooperate, and why tools like empathy and language evolved to enable that cooperation. All else of human nature is derivative of this single human condition.

Empathy and violence, tribalism and warfare, storytelling, dance, and music—all derivative.

Our business as we go forward is to build the case for your well-being as it is built in humans: in mind, body, energetics, and motion, in the elements of life.

But understand from the beginning that evolution—working in bone, muscle, neurons, fat, food, and fight—finally built a creature that is human. How are we different from all the rest of life? The paleoanthropologist Ian Tattersall offers a good summary. “To put this at its most elementary, humans care at least to some extent about each other’s welfare; and chimpanzees—as well as probably all of our other primate relatives—do not.”

Our other primate relatives did not—at least not to the extent that we do—and they are extinct.

Excerpted from GO WILD: Free Your Body and Mind From the Afflictions of Civilization by John J. Ratey, MD and Richard Manning.

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