Humans are a puzzling species. On the one hand, we struggle to survive on our own in the wild, often unable to solve basic problems, like obtaining food, building shelters or avoiding predators. On the other hand, human groups have produced innovative technologies, sophisticated languages, and complex institutions that have permitted us to successfully expand into environments across the globe. What has enabled us to dominate such a vast range of environments, more than any other species? The Secret of Our Success lies not in our innate intelligence, but in our collective brains—in the ability of human groups to socially interconnect and to learn from one another.

Drawing insights from lost European explorers, clever chimpanzees, hunter-gatherers, neuroscientists, ancient bones, and the human genome, Joseph Henrich demonstrates how our collective brains have propelled our species’ genetic evolution, and shaped our biology. Our early capacities for learning from others produced many innovations, such as fire, cooking, water containers, plant knowledge and projectile weapons, which in turn drove the expansion of our brains and altered our physiology, anatomy and psychology in crucial ways. Further on, some collective brains generated and recombined powerful concepts, such as the lever, wheel, screw and writing. Henrich shows how our genetics and biology are inextricably interwoven with cultural evolution, and that this unique culture-gene interaction has propelled our species on a unique evolutionary trajectory.

Tracking clues from our ancient past to the present, The Secret of Our Success explores how our cultural and social natures produce a collective intelligence that explains both our species striking uniqueness and odd peculiarities.

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Much existing literature in anthropology suggests that teaching is rare in non-Western societies, and that cultural transmission is mostly vertical (parent-to-offspring). However, applications of evolutionary theory to humans predict both teaching and non-vertical transmission of culturally learned skills, behaviors, and knowledge should be common cross-culturally. Here, we review this body of theory to derive predictions about when teaching and non-vertical transmission should be adaptive, and thus more likely to be observed empirically. Using three interviews conducted with rural Fijian populations, we find that parents are more likely to teach than are other kin types, high-skill and highly valued domains are more likely to be taught, and oblique transmission is associated with high-skill domains, which are learned later in life. Finally, we conclude that the apparent conflict between theory and empirical evidence is due to a mismatch of theoretical hypotheses and empirical claims across disciplines, and we reconcile theory with the existing literature in light of our results.