It’s not our intelligence. The immense dominance of our species is not due to our raw, innate intelligence, or our individual brainpower, as is commonly believed. 

When stripped of the relevant culturally-trained mental skills and acquired know-how, we humans do not outperform other apes in cognitive tests. When stranded in remote regions, where hunter-gatherers have survived and thrive for millennia, we flounder, unable to find food, locate water or travel effectively. If our big brains are for surviving as hunter-gatherers, or for solving novel problems, why are we so bad at tackling such basic challenges? 

It’s our collective brains. Instead of individual brainpower, our ability to generate sophisticated technologies, immense bodies of know-how, and cooperation-enhancing institutions arise from a combination of our imitative abilities and our sociality. 

Learning from each other over generations, often well outside of conscious awareness, gives rise to steadily improved practices, techniques and technologies that are not understood by those using them. This process easily generates innovations without invention or insight. For example, unbeknownst to most who love spicy foods, the particular spices used in hot climates kill the pathogens in meat, effectively protecting those using these recipes from infections. This is why hot climates are spicier. In the New World, many populations added wood ash or burnt seashells to their corn recipes. Without these chemical additions, relying on corn as a staple results in deficiencies and the horrible disease, pellagra. In Fiji, taboos on particular marine species protect pregnant and breastfeeding women from dangerous toxins.  

Culture became the primary driver in human genetic evolution, making us the world’s only cultural species. Our accumulating body of increasingly complex know-how about tools, plants, animals, fire, cooking, shelters and food processing as well as tools like spears, knives, and water containers drove, and continue to drive, our species’ genetic evolution.

People don’t instinctively know how to start fires or cook. Yet, these learned abilities and practices have altered our genetic evolution to shrink our teeth, gapes, stomachs and colons, in part to free up energy for building our big brains. Similarly, the complexity of our technologies and spoken languages have been created by cumulative cultural evolution, but these in turn have driven our larynx down, improved our dexterity, altered our hands, whitened our eyes and spring-loaded our shoulders. This culture-driven genetic evolution also gave us an entirely new form of status, called prestige. 

Over centuries or millennia the forces of intergroup competition have selected many social norms and institutions because of how they benefit societies.

Communal rituals often involve music, dance and synchrony as well as terrifying rites and pain. Such rituals have emerged and spread widely through human societies, including among the smallest scale populations of hunter-gatherers, because of how they galvanize our sociality. Psychologically, these rituals were selected by non-conscious cultural processes to build strong social bonds among individuals, often from distant groups, because of how various ritual elements tap into and manipulate basic aspects of our psychology. Rituals help even the smallest scale human societies build large and more enduring networks, societies and institutions.

Through a process of self-domestication, social norms and institutions, such as those related to rituals, food sharing and marriage, became the primary selection pressures shaping our genes to alter our sociality.

Culture directly shapes our brains, influences our hormonal response and immune reactions as well as our attention, perceptions, motivations and reasoning processes. People who grow up in different cultural environments are biologically different, even if they aren’t genetically different.

Learning to read, which has only become widespread in recent centuries, constructs a specialized network in the left ventral occipital temporal region of our brains, pushes face-processing into the right hemisphere and thickens the corpus callosum, the information highway that connects the two hemispheres of our brains. These neurological renovations result in (1) rapid, automatic and non-conscious recognition of the symbols of the particular writing system, (2) longer verbal memories, (3) broader patterns of brain activation for spoken words, (4) a greater awareness of the various sounds that make up words, and (5) reduced facial recognition skills. Most people, across most of human history, lacked these neurological and cognitive modifications.     

Human psychology and behavior cannot be fully understood except in the light of culture-driven genetic evolution. Culture has driven our species into what biologists call a major transition, a transformation into a new kind of animal. Our species has long been completely addicted to culture for our very survival; yet, the production of the know-how, innovations and institutions that permit us to thrive depend not on our individual intelligence, but on the institutions that hold our collective brains together. Only by understanding this coevolutionary duet between genes and culture can we explain (1) why humans are unique, (2) why we are so cooperative while at the same time so warlike, and (3) why we seem so smart compared to other animals.