3. Human Nature and Hunter-Gatherer Communities

How and why did humans evolve away from their common ancestor with the chimpanzee? About five million years ago, chimp-like primates lived in the forests of Africa. At some point a serious drought caused the forest to shrink. Some animals stuck to the trees, but others ventured into the open land in search of food. This was tiring because four legs are good for short bursts of speed but less good for endurance. Natural selection gradually favored chimps that could walk upright. This freed up the front legs—or hands—that the chimps could then use for other endeavors; dexterity was especially advantageous. It also became evident that those with less hair were better at thermoregulation. They could stay active during the day when dangerous predators were hiding. The first primate with bipedal locomotion was Ardipithecus ramidus.

Homo habilis, Homo erectus, Homo heidelbergesis, Homo neanderthalensis, and finally Homo sapiens followed over the next few million years.  Tools were used, migration continued, fire was discovered, the brain expanded, and art was created. Hominid species began to evolve into hunter-gatherers. Homo sapiens lived in hunter-gatherer villages; it’s important to note that ninety-nine percent of humanity has lived in such communities, right up until the First Agricultural Revolution. Many of our unique human adaptations were designed for this hunter-gatherer environment. 

It was a highly active lifestyle. Women traveled around five or six miles a day gathering plants, fruits, nuts, seeds, potatoes, and mushrooms. Along with their collection, they also carried children and water. (Why do you think women like bags and totes?) Men hunted animals, both large and small. They covered up to ten miles a day, with periods of exertion including sprinting and spear throwing. Likely because of these activities, men evolved to be somewhat better at spatial navigation. (Modern-day sports contain shadows of our hunting past, requiring energy, skill, and most of all, teamwork.) Finding enough food was a full-time occupation involving everyone. Our nervous system values feelings of productivity because it generally results in the resources needed to survive. 

Similarly significant was these communities’ highly social nature. Villages consisted of thirty to 150 people, so you generally knew everyone and were never alone. Important relationships were with mates, friends, family, and trading partners. Women were pregnant more often than not. Life was dangerous and challenging, and this provided a foundation for very strong social bonds. Hunting and gathering worked best when humans cooperated. Natural selection began favoring qualities such as trust and loyalty and discarding the extreme aggression you see in chimps. Being able to read social cues became necessary. (In fact, if you can see the white in a species’ eye, it often means they are a social creature because it’s easier to read their intentions.) All this is also crucial to the trade that eventually happened within and between communities. There were strong feelings of group cohesion and alliance to your village, reflected in today’s in-group and out-group biases and wariness of strangers, especially if they do not look like you. Additionally, hunting encouraged reciprocal altruism (kindness with the expectation of a return) because one person cannot eat an entire animal. The successful hunter shared on his lucky week, someone else would share on another. A hunting victory meant more than merely food; it brought with it status that was crucial in finding a high-quality mate. Regardless of gender, individual contribution to the village was of utmost importance—a feeling we still seek today. 

Food and cooperation are key elements. So is brain size, and here is how they are related: It seems self-evident that a big brain is good for survival and reproduction. However, it’s a costly organ, using up a huge amount of the body’s resting energy budget. To a lesser degree, this is also true for our intestines; digesting raw meat and uncooked plants is energy-intensive. Yet once we learned to cook our meals, the gut shrank, and all that extra energy could go into brain development. It also cut down on disease, which freed up the pressure on the immune system. Additionally, humans began to form pair bonds, that is, relationships in which both parents invest in raising the child. This additional protection allowed the offspring to be born prematurely, and the brain could keep growing substantially outside of the womb. A bigger brain is useful for cooperation, communication, impulse control, complex interactions, and developing a theory of mind (predicting the thoughts and feelings of others), so evolution ran with it. 

Because this invaluable organ requires so much energy, and because hunter-gatherers are always on the move, the body became extremely good at storing fat so the brain wouldn’t run out of energy during frequent times of food scarcity. It also has an energy conservation mechanism, which tells us to rest whenever possible. This all works efficiently, providing that the environment doesn’t change too drastically. You’ll see children ostensibly wasting energy, but play actually is essential practice for skills later in life.

Such was the way of life for approximately 2.5 million years. However, about ten thousand to fifteen thousand years ago, humans began out-reproducing their food supplies. In response, they began farming and domesticating animals. This tied them to one place; the advent of private property led to a wealth disparity. In many ways accumulating wealth relies on delayed gratification (a quintessential human characteristic), and because the wealthy had more children, we began to see a rise in the trait of conscientiousness. Note how the changing environment shapes us, just as the transition from trees to land selected the agreeableness needed for collaboration. 

However, evolution takes place significantly slower than the environment can change, and this sometimes creates an evolutionary mismatch. The neural pathways created over millions of years continue to affect our psychology, but no longer always match our surroundings. Here are three examples, which will sound familiar based on the hallmark features of our hunter-gatherer past: the drive to seek food, high levels of activity, and tight-knit communities. 

Remember that the brain needs a lot of fuel to function, so we evolved preferences to consume as much calorie-dense food as possible. However, this assumes that our environment contains mainly plants and lean meat. Now we fervently continue to seek out nutrition, but many of our choices are highly processed food loaded with sugar and fat. This leads to a host of so-called mismatch-diseases, which will not be selected out because evolution depends on differential reproductive success—because such afflictions often affect people later in life, they can still pass on genes.   

Furthermore, most people no longer walk and run six to ten strenuous miles a day. Many of the body’s systems, such as the mood-regulating mechanism, do not function optimally under near-sedentary conditions. According to the costly repair hypothesis, the body doesn’t activate the natural repair mechanisms until it senses sufficient stress in the form of exercise. In its absence, many aversive processes take place, such as inflammation buildup in the cells. However, exercise goes against instinct because of the energy conservation mechanism. You are supposed to conserve calories, not burn them frivolously. However, this mechanism takes for granted that you are already active all day because this is what was happening for millions of years. 

The texture of our social environment has also changed, but our need for engagement and belonging has not. For the most part, we no longer spend our entire lives in close proximity eating, sleeping, working, and interacting with the same fifty people. Trusting others is no longer a matter of life and death, and the fierce intensity and vulnerability in relationship dynamics is lost. We were not designed to speak on a computer but rather to read body language and have physical contact. The result can be loneliness. Many people today report having no sense of purpose or meaning and long for more connection. Hunter-gatherers would likely not have felt such a longing due to the close community and the individual’s essential contributions to the village. 

The modern environment is also full of supernormal stimuli, or artificial input, that the system was not designed to handle. The result is maladaptive behavioral responses. Some examples of these stimuli include excessively sweet foods, alcohol, drugs, social media, technology, advertising, artificial lighting, pornography, and video games. They essentially exploit existing neural circuits by causing an exaggerated response that might be pleasurable in the short term but can lead to addiction, isolation, sleep disturbances, or other health problems. 

The take-home message is that our past matters because evolution shaped us to thrive in that environment. In the words of evolutionary psychologist David Buss, to understand the product you have to look at the process. Now that we have the background, we’ll dive right into some of the concepts at the core of evolutionary psychology in the next two sections. 

*The information from this section is primarily from A Troublesome Inheritance by Nicholas Wade, and The Story of the Human Body by Daniel E. Lieberman.