A Hunter-Gatherer's Guide to the 21st Century: Evolution and the Challenges of Modern Life

by Heather E. Heying

The descendants of the Beringians would come to populate the Americas in total isolation from all human populations in the Old World. They arrived before any humans on Earth had invented written language or agriculture; independent of any input from their Old World relatives, they innovated these things from scratch. Their lineage would discover hundreds of new ways of being human, and rise to an estimated population of fifty million to one hundred million before Spanish conquistadors brought the Old and New World populations into violent reconnection many thousands of years later.

Conscious thoughts are those that can be communicated to others. We define consciousness, therefore, as “that fraction of cognition that is packaged for exchange.” This is no trick. We have not chosen a definition to make an intractable question simple. We have chosen the definition at the epicenter of what people mean when describing a thought as “conscious.”

We plug our minds into a shared problem-solving space and share what we know. Then we parallel process—proposing hypotheses, providing observations, offering challenges—until we arrive at a new answer, one that an individual would rarely reach alone. If the result works well when tested in the world, it gets refined and then driven into a more automatic, less deliberative layer. This is culture. The application of culture to the circumstances for which it is adapted is the population-level equivalent of an individual being in the zone.

All else being equal, a creature that is a better fit for the environment tends to produce more offspring, and when that is the case, biologists have excellent conceptual tools for unpacking the evolutionary process that leads to it. What happens when all else isn’t equal, however, and the creature with more offspring has cut corners in the pursuit of short-term fecundity? Under these conditions the ability of biologists to understand the story is compromised.

If the harm done to fitness shows up quickly—if an individual animal produces many offspring, all of which perish in the winter—we will likely come to understand that it failed in an evolutionary sense. If, however, the descendants prosper for a fairly long time, but die off in the next drought, or the next Ice Age, there is a good chance biologists will botch our analysis of “success.”

In the 21st century, nearly everyone accepts that evolution has created our limbs and our livers, our hair and our hearts. Yet many people still object when evolutionary theory is invoked to explain behavior or culture.14 Even for many scientists, this position is driven by the belief that some questions should not be asked if the answers to them might be ugly. This has led to ideologically driven censorship of ideas and research programs, which has slowed the rate at which we have enhanced our understanding of who we are, and why.

From the genome’s perspective, culture is anything but free. In fact, nothing is more costly. The brain that picks up culture is big and energetically expensive to run; the process by which culture is transmitted is prone to error; and the content of human culture frequently blocks off fitness-enhancing opportunities—thou shalt not kill, steal, covet, lay with, etcetera. Anthropomorphizing the genome for a moment: If culture did not pay the genome back for its astronomical expense, the genome would have reason to be livid. Culture appears to waste time, energy, and resources that would otherwise be at the genome’s disposal. One might get the impression that culture is effectively parasitizing the genome.

From the Omega principle we derive a powerful concept: any expensive and long-lasting cultural trait (such as traditions passed down within a lineage for thousands of years) should be presumed to be adaptive.

Other traits evolve once and then stick, suggesting that their value is nearly universal. No organisms that once evolved bony internal skeletons have since evolved a lifestyle without them. The same holds for neurons and for hearts.

There is still disagreement about how long it took mammals to begin to diversify, to turn into the great chaotic mess of nearly five thousand mammal species extant on the planet today—half of which are rodents, another quarter of which are bats, and the remaining quarter of which include forms as varied as dolphins and kangaroos, elephant seals and antelope, rhinoceroses and lemurs.

Just as mammals before us got brainier relative to their ancestors, we primates got brainier, too, compared to the other mammals. At the same time, gestation length expanded—babies cooked for longer inside mom before being born. Litter size fell, so mothers had fewer children at a time to tend to. The period of parental investment after birth lengthened and intensified, and sexual development happened later and later, giving ever more time for young primates to learn how to feel, how to think, how to be.

Monkeys have singletons or twins rather than litters—and accordingly, all the extra sets of nipples disappeared, the ones that would never be needed to feed young . . . except the ones on males. With even fewer babies to tend to at a time, monkey mothers—and far more rarely, monkey fathers—spent more time with each child, teaching it how to be a monkey.

Other conditions, though, are particular to the individual: Is your body ready for its first pregnancy? If you’ve had previous pregnancies, how old is your youngest child? Is she weaned? Do you have older children around to help? Sisters or friends? Your preferred mate? When breeding seasons were the rule, reproductive timing was synced up, so there was lower variance in the answers to these questions. It was also easier, with breeding seasons, for a single male to monopolize the reproductive efforts of several females. With individual cycles, male monopolization of female reproduction is more difficult, which lays the groundwork for relationships between individual males and females to evolve—for monogamy, and biparental care, to evolve.

Among those imagining a chimpy past, without recognizing that this is what he was doing, was 17th-century philosopher Thomas Hobbes, who famously declared that humans, in our “state of nature” (that is, without government), are destined to live lives that are “solitary, poor, nasty, brutish, and short.”21 More recently, intellectual luminaries from Sigmund Freud to Steven Pinker have, similarly, imagined that humans need civilization to save us from our basest instincts. It is true that chimps tend toward war rather than peace, and are often found fighting at the edges of their territories. Bonobos, in comparison, tend toward peace rather than war, and at the edges of their territories, they’re more likely to be sharing food with another troop than beating up on each other. But humans engage in both war and peace. Whether we take up arms when strangers show up at our door, or provide alms and invite them in to share food with us, is highly variable across both cultures and contexts. Given that we are exactly as equally related to both chimps and bonobos, looking to one rather than the other for insight into what humans are makes little sense. We have much to learn from both.

Furthermore, standing up on two legs had cascading effects throughout the body, including, ultimately, the restructuring of the human vocal tract, such that we can now create more sounds than any other animal of similar cognitive ability. It is possible that becoming bipedal was a necessary precursor to having speech.

Ten to twelve thousand years ago, people were beginning to farm. By nine thousand years ago, permanent settlements were forming; in the Middle East, Jericho may have been Earth’s first city. Eight thousand years ago, at Chobshi, in the Andes of modern Ecuador, people took cover in a shallow cave, and hunted by funneling guinea pigs, rabbits, and porcupines off a short cliff, retrieving the corpses at the bottom, with which they made food and clothing.30 By three thousand years ago, much of Earth’s landscape had been modified by human activity—by hunter-gatherers, by agriculturalists, and by pastoralists.31 Seven hundred years ago, some humans were in Europe, and many of them died of famine. Not too many years later, many more succumbed to the Black Death. Some humans were in China, living under Kublai Khan’s rule, whose empire had greater geographic reach than any empire before. Some humans were in Mesoamerica, beyond the reach of Khan, living in the embrace of the Mayan Enlightenment.32 Across the planet, humans lived in a multitude of cultures, political systems, and social systems. Most populations knew little about life beyond their borders—they knew only of their nearest neighbors. Seven hundred years ago, only a very few people were connecting with others halfway around the world, sharing ideas, food, language. And those few were restricted to the speed of sail and horses, rather than nearly the speed of light.

Now that we understand something of our deep history, and how long it has taken to become human, we can begin to explore modern innovations—and understand more fully the implications of our ancient history and how it shapes our relationship with modernity. We are experiencing changes across the full spectrum of our experience: to our bodies, our diet, our sleep, and so much more. Many of these changes have come so fast and furious that we should not be surprised when they create damage that is difficult to undo.

Thus, appendicitis is a disorder of the WEIRD world. So, too, are many allergies and autoimmune disorders, for which there is solid, and growing, evidence to support the “hygiene hypothesis.” The hygiene hypothesis posits that because we live in ever-cleaner surroundings, and are therefore exposed to ever fewer microorganisms, our immune systems are inadequately prepared, and so develop regulatory problems, such as allergies, autoimmune disorders, and perhaps even some cancers.17 Our immune systems are not functioning as they evolved to do, suggests the hygiene hypothesis, because we have cleansed our environments too thoroughly.

Our appendix seems likely to have suffered the same fate as our immune systems. Absent frequent bouts of diarrhea, which are the body’s way of ridding itself of pathogenic gut bacteria, the appendix turns from being an important repository of good bacteria to being a liability.

But because milk is meant to be consumed immediately, with little or no contact with the outside world, milk has no defense against environmental bacteria, and we moderns must go to extreme lengths—pasteurization, hermetic sealing followed by refrigeration—just to preserve milk for a week or two. Clearly, an ancestor who needed to preserve milk over a long and unproductive winter would have needed a better solution. One of those solutions is cheese. By rotting milk carefully, using specially cultivated bacteria and fungi that are not pathogenic to humans, milk can be preserved indefinitely. Cheese is such an elegant solution to the problem that, once made, even a block of cheese that is colonized by bad bacteria on the outside can have a thin layer of its surface removed to reveal the fresh, untainted cheese beneath.

Related to the reductionist thinking around vitamin D is the fact that for decades now, we have received a nearly universal recommendation to slather ourselves with sunscreen whenever we’re in the sun.15 Reduce your exposure to the sun, the logic goes, and skin cancer rates fall. True enough. Guess what goes up when sun exposure goes down, though: blood pressure. And as blood pressure climbs, so do rates of heart disease and stroke. People who avoid the sun have higher overall mortality rates than do people who seek it. A research study on Swedish women reported this remarkable result: “Nonsmokers who avoided sun exposure had a life expectancy similar to smokers in the highest sun exposure group, indicating that avoidance of sun exposure is a risk factor for death of a similar magnitude as smoking.”16 So reductionist scientism has misled us yet again, and likely caused many deaths. Should we stay out of the sun and take vitamin D, or seek moderate sun exposure and get the nutrients we need by seeking something closer to an ancestral diet? An evolutionary analysis suggests the latter. At least on this topic, the medical literature is catching

In February 2020, early in the COVID-19 pandemic, both the World Health Organization (WHO) and the US surgeon general repeatedly told the public that “masks aren’t helpful” in protecting against SARS-CoV-2.20 In this case, too many people listened to the authorities rather than thinking through the logic themselves. Why, for instance, if masks are pointless, are they exactly the equipment used by health professionals when trying to avoid infection from respiratory ailments? When the directives were later reversed, people who had followed them based on authority alone lost faith in those same authorities. It was then difficult to regain the public’s trust sufficiently to encourage a careful, nuanced approach to reducing the spread and impact of this novel coronavirus. Simple prescriptions make snappier sound bites, and they are easier to remember for those looking for set-and-forget solutions, but when they fail you, you are left with nowhere to stand, no ability to problem solve for yourself. Rather than blindly “trusting the science” or following the lead of authorities, learn to do at least some of the logic for yourself, and seek authorities who are willing to both show you how they arrived at their conclusions and admit when they have made mistakes. Again, our hope is that we can help you become a better problem solver.

Spend time in nature, the less constructed and controlled the better. This has many benefits, among them the dawning recognition that you cannot control everything in your life, and that experiencing discomfort—even the slight discomforts of a too-warm day, or rain for which you are unprepared—calibrates your appreciation for other aspects of your life.

Be barefoot as often as possible. Calluses are nature’s shoes, and they do a far better job of transmitting tactile information to your brain than do shoes.22

The second misguided assumption that many such diets reveal is that they seem to presume that food is merely for survival. The evolutionary truth is that food is for more than just survival. Food is more than nutrients, vitamins, and calories. Like all animals, indeed all heterotrophs, we eat to acquire the energy and nutrients necessary to be alive. But the human relationship with food, like that with sex, has expanded beyond its original purpose. Humans no longer eat merely to satisfy energetic requirements, any more than we have sex just to make babies.

Instead of chasing the newest diet advice with processed food—now with more B12!—we should be eating real food. Real food is that in which the base ingredients are recognizable as coming from a living organism (there are just a few exceptions, like salt).

When those journeys were across water, they could have been facilitated by fire, in part because, under many circumstances, burning out the hulls of trees to make them into canoes is a faster route to having a functional boat than is carving. Being able to take fire with us also opened up territory that was colder than anything we could have survived without it, allowing for exploration of the entire globe. And the control of fire led to the invention of cooking, which saved both time and energy, and ultimately led to the proliferation of cuisines and methods that we have today.

Of the food that we eat, which of it has an interest in being eaten? That is, what foods were produced by the organism with the expectation that their product would be eaten? Milk, fruit, and nectar. That’s all.

Chewing on sugarcane is to eating refined sugar as chewing on coca leaves is to snorting cocaine. Highly refined foods (aka “highly processed foods”) are another example of hyper-novelty, as is plastic, so try to avoid food packaged in plastic, and especially avoid allowing hot plastic to touch your food.

Expose children to a diverse range of whole foods, especially ones that connect them to your culinary and ethnic background. Eat the same food that you put in front of them, and show obvious enjoyment of it. Keep seasonal produce on your counter, and let the children eat any fruit that they find there, encouraging them to develop their own preferences while they also learn how and when to explore a variety of whole foods.

When a hunter-gatherer finds honey that he can separate from its bees, he and his friends will likely gorge on it, for there is no knowing when the next burst of sugary goodness will come their way again.32 But since food resources are no longer scarce, gorging is not an effective strategy, because the scarcity never comes. Instead, we get more opportunities to gorge. We have to willfully override our evolutionary impulses in order not to suffer the hyper-novelty that the twenty-four-hour grocery store provides. Putting yourself on a schedule, as intermittent fasting recommends, of not eating for regular periods of time seems to be a healthful corrective.

Sleep almost certainly came to be part of our lives as the result of a simple trade-off: it is impossible to build an eye that is optimized for both day and night. You could have two sets of eyes, but it would be impossible to build a visual cortex optimized for both without vastly increasing the brain’s size and energy requirements.

For humans, in particular, it would be a shame to take the marvelous computer that we have riding around on our shoulders and totally sideline it during the night, just because our eyes are out of their depth. Because even when we can’t literally see what is going on in the world, we can consider what we’ve already seen. In response, selection has borrowed the incredible computing power that exists in our visual apparatus and repurposed it for a kind of moviemaking. We are physically dormant at night, but not mentally so.

In sleep, we predict and imagine what we might see in the future, and do a bit of scenario building around the possibilities. So that next time, we know what to say, how to feel. So that next time, we are prepared.

During slow-wave sleep, our brains fix memories in place—as do the brains of great apes, including chimpanzees.5 Our brains also prune out old and redundant information during slow-wave sleep and gain mastery over skills that we learn while awake—typing, skiing, calculus. Hence the adage to “sleep on it.”

Once selection discovers that there are useful ways to utilize a mind during bodily dormancy, it discovers all kinds of utility, and sooner or later, individuals become dependent on their ability to access this state. Our bodies and brains, linguistic and emotional lives, social and behavioral repertoire are all dependent on sleep.6

organisms put a lot of work into discouraging the consumption of their body parts. Structural barriers are one method—cactus spines, porcupine quills, turtle shells. Another is poison, but it is often too crude to be maximally effective. If a deer dies after eating foxglove, the deer will be replaced by another deer that knows nothing of the plant’s poison. On the other hand, if a deer expands its dietary repertoire to include Psilocybe mushrooms, and spends the rest of the day having a temporary psychotic break, it may well look elsewhere for its next meal, having been educated, and perhaps terrorized, rather than killed.

And caffeine, which disincentivizes herbivores from eating caffeinated seeds at high concentrations, may also be a kind of pharmacological social engineering on the part of the plants. When bees are given sugar rewards that contain caffeine, their spatial memory improves threefold; the caffeinated nectar of both citrus and coffee flowers may well be priming their pollinators, the bees, to remember them and to come back for more.7

In alligators, the temperature of an egg as it develops determines the sex of its inhabitant: low temperatures create females, high temps make males. The same is true for tortoises, but the outcomes are reversed—cool eggs produce males, warm ones produce females. And in crocodiles and snapping turtles, intermediate temperatures produce males, while either extreme produces females.

Humans are sexually dimorphic across many domains, extending far beyond reproduction. Men and women have different disease risks, etiology, and progression, for conditions from Alzheimer’s9 to migraine,10 from drug addiction11 to Parkinson’s disease.12 Our brains are structured differently.13 We tend to have different personality traits by sex, and they are mediated by our environment: personality differences are greater in countries that have abundant food and a low prevalence of pathogens.14 In general, women are more altruistic, trusting, and compliant as well as more prone to depression than men.15 Men are more likely to be diagnosed with ADHD,16 women are more likely to have anxiety disorders.17 Finally, on average, men prefer working with things, and women prefer working with people.18

Among sequential hermaphrodites like flame wrasses, after a female changes into a male, he has changed not only his sex—which gamete he produces, once eggs, now sperm—but also his “sex role,” which is the behavioral expression of his (new) sex. In humans, we call this gender, or sometimes, gender expression.

The usual rules of sex roles, then, are ones of male display and female choosiness. This stems from that long-ago difference in investment between the sexes—the large resource-rich egg and the small streamlined sperm. Furthermore, in those species in which parental care is necessary for the offspring to survive—which means all of mammals and birds, and a good proportion of reptiles, amphibians, fish, and insects as well—males tend to put more effort into what happens before sex, and females put more effort into what happens afterward.26

To put it in strictly evolutionary terms, in the vast majority of species, females are the limiting sex. Because females invest more in offspring—from eggs being larger than sperm through parental care typically (though not always) falling to females more than males—males must compete for access to females, and females get to choose among their suitors. Males thus tend to be larger (think elephant seals) or more aggressive (e.g., woolly monkeys); or gaudier (peacocks), louder (nearly all frogs), or more melodious (mockingbirds) than the females of the species.

Still, sex-role reversal—what we might call gender switching in humans—is not the same as changing sex. In mammals and birds, with our genetic sex determination, there is no sex change possible—no pigeon or parrot, no horse or human, has ever changed what sex they actually are. Behavior, though—call it sex role, call it gender—that is highly labile (open to change). We humans are the most labile, behaviorally, of all the animals. So it shouldn’t surprise us too much that many of us are abandoning some old gender norms—behaviors that have, in the past, been tightly coupled with our sex—and configuring new ones.

Gender is more fluid than sex, and has many more manifestations, but “acting feminine” (gender) is not the same as “being female” (sex).

In no other species of primate do breasts persist when there are no babies around to benefit. Human breasts are sexually selected, and they are doing more than feeding babies. They are also advertisements to men—just as a lyrebird’s song and a rutting boar’s smell28 and a red-capped manakin’s dance are advertisements to the females of those species.

The concealment of ovulation in humans is also sexually selected. While nearly all mammals advertise fertility by physiological means, humans do not—or at least, we do so far less than other species. We have also become sexually receptive throughout the year, rather than just seasonally. Concealment of ovulation serves some reproductive ends, but it also encourages something that humans do a lot of: we engage in nonreproductive sex—sex for pleasure, sex for bonding.

Jump forward to the human transformation of landscapes with agriculture, and gender roles became even more constrained. Being tied to a particular piece of land, we were now more sedentary and had ample grain stores with which to supplement our and our children’s diets at any time. Agriculturalist women thus experienced a decrease in the birth interval—babies came at a faster rate—and so the birth rate climbed.31 This increase in fertility tied women to hearth and home, and we saw a concomitant decrease in women’s roles in economic, religious, and other culturally important realms.

Some of the average differences between the sexes include that men have more “investigative” interests, while women have more “artistic” and “social” interests.32 Men are also, on average, more interested in math, science, and engineering.33 On tests, girls score higher in literacy, while boys score higher in math.34 And although average intelligence is the same between boys and girls, the variability in intelligence is not: there are more boy geniuses, and more boy complete dullards, than there are girls in either category.

One interesting piece of neuroscience reveals that, across several domains—including both emotional memory and spatial ability—women are better at details, men are better at “gist.” This finding manifests, for instance, in the average man’s superior ability to remember a route, and the average woman’s superior ability to remember the location of the keys, the cup of coffee, the document in need of being signed.