Starting in the late 1970s and early 1980s, a new program of research began to emerge in the study of human culture and behavior. Building on pre-existing tools from population genetics and evolutionary biology, researchers like Luigi Cavalli-Sforza, Marcus Feldman, Robert Boyd, and Peter Richerson began to construct a theory of cultural evolution rooted in Darwinian principles. They showed that attention to the functional roots of culture could be couched in a larger framework capable of explaining both the nature of culture and the processes behind cultural change.

The notion that cultures evolve was hardly new. Archaeologists and anthropologists had been working under that assumption for a few decades, striving to refine their theoretical and methodological approaches into the roots of a mature, rigorous science. Ultimately, these efforts yielded a framework that used a thoroughly Darwinian lexicon – adaptation, selection, evolution – in only loosely Darwinian ways. Researchers developed a focus on local ecological specialization – a useful step forward – but frequently situated their insights in a framework that was both incomplete and inconsistent. The recognition that cultural change was not only evolutionary, but sensibly Darwinian, provided the tools necessary to build formal – and testable – explanations of cultural phenomena.

In the years since Cavalli-Sforza, Feldman, Boyd, and Richerson laid down their pioneering work, the theory of cultural evolution as a Darwinian process – capable of both causing and responding to new patterns of biological evolution – has been consistently vindicated, demonstrating its utility in the lab and field. Joseph Henrich’s book, The Secret of Our Success is a thrilling exploration of the frontiers of that research. Henrich puts up a strong case that underlying humanity’s broad ecological success and expansive behavioral repertoire is our faculty for creating, transmitting, manipulating, storing, and accumulating massive amounts of non-genetic information in the form of culture.

Cumulative cultural evolution, as it is called, is unique to humans (putting aside emerging evidence for simple forms in New Caledonian crows – the difference in degree is large enough that we might as well call it one of kind). Other species have cultural traditions – those crows, for instance, make tools, as do chimpanzees – but none of them retain that information and build on it in any meaningful way over successive generations. The techniques individual chimps learn for termite fishing or nut-cracking are lost at death, inevitably hung up on the barriers that inhibit the transmission of all the other traits organisms acquire throughout their lifetimes.

In technical parlance, this is called Weismann’s barrier. Put simply, it means that inheritance is a one way street – information moves from germ (sex) cells to somatic (body/tissue) cells, but not the other way around. A chimp might learn a great deal about how to use tools to access otherwise inaccessible resources throughout its lifetime, but it has no way to get that information from the neurons in its brain to the eggs or sperm in its reproductive system.

Somewhere in the hominid line, our ancestors found a way around that obstacle, sidestepping the whole business of one-way genetic transmission by transmitting lifetime’s worth of acquired information from individual to individual in the form of culture. The foundations of this remarkable evolutionary transition rest in humanity’s a spectacular facility for social learning. Other species are, of course, capable of social learning, but these abilities are vastly enhanced in humans. We pay far more attention to each other than other animals, selectively targeting individuals that exhibit signals of above-average proficiency or expertise. In the same vein, we have a highly developed theory of mind (the ability to think about what other people are thinking) allowing us to understand each other in terms of intentionality and purpose. It has even been suggested that our unusually small iris, set against a very white sclera, is an adaptation for non-verbal communication – making it easier for us to keep track of other people’s attention and communicate our own.

Critically, growing evidence indicates our social learning expertise – unlike many other forms of human knowledge and behavior – is innate. Henrich discusses experiments in which children matched against adult chimps and orangutans on a variety of tasks. In most domains, they do about the same or a little worse than the other primates. But in social learning, human children massively outperform their hairier cousins.

Such highly evolved adaptations for social learning provide a scaffold for extraordinary levels of information sharing. Even absent language, humans watch one another and pay special attention to signals of above average proficiency and prestige in order to learn new or better ways to solve adaptive challenges. They create and maintain social norms that encourage cooperation, foster stable traditions, and aid in patterns of ingroup-outgroup competition. Social learning allows us to make and accumulate culture.

This, more than anything else, explains why a species with relatively little genetic variation displays such a sweeping range of behavioral variation and ecological specialization. It gets to the why of the of descriptive insights uncovered by earlier cultural evolutionists – that humans display local ecological adaptation – by presenting a plausible and, increasingly, empirically justified mechanism. Humans can meet the challenges of living on frigid ice sheets in the high arctic and sweltering jungles in the subtropics because we have the capacity to accumulate information about how to live in those environments at a rate far in excess of that afforded by strict biological adaptation. And critically, it’s not a matter of individual genius. Humans learn about how to live in new environments through the accumulated wisdom of generations of trial-and-error learning, resulting in cultural packages that are expertly tailored to the challenges of specific ecosystems.

Clearly, this point stands in contradiction to those who would link humanity’s extreme success as a species to extraordinary – and innate – individual intelligence. Individual humans can be pretty smart, but they rarely (if ever) have the cognitive horsepower necessary to build the sophisticated cultural innovations necessary to survive in novel environments from scratch. This is true of modern technology and scientific progress as much as it is of forager subsistence and ritual observance. There is a popular tendency to think of technological innovation as a matter of lone geniuses and marvelous insights. But James Watt’s steam engine was inspired by the earlier Newcomen steam engine. Similarly, Albert Einstein’s theories of special and general relativity drew inspiration and built on insights from the work of Gottfried Leibniz and Bernhard Reimann. Individual genius is real (who could argue that Einstein wasn’t a genius?) but the fruits of genius accrue incrementally.

For his purposes, Henrich makes this point another way. To illustrate the failings of individual intelligence – and, by contrast, the power of cumulative cultural evolution – he relates a variety of historical anecdotes . In this light, we might think of them a little natural experiments. In each, healthy, intelligent European explorers found themselves in a scenario where they are forced to survive on their wits alone in an unfamiliar environment. Be it the muggy, swampy coasts of the Gulf of Mexico, the icy wastes of the high arctic, or the arid sprawl of the Australian outback, the outcome is inevitably the same: suffering and death. Those that survived did so because kindly natives, with the cumulative knowledge necessary to survive in a particular ecosystem, lent the naive Europeans a hand.

Tellingly, the causal mechanics of successful cultural adaptations are usually opaque to the people who employ and perpetuate them. Most people don’t understand the physics of bow and arrow technology or the insulative properties of snow and ice. They don’t understand the chemistry of effective poisons for hunting or detoxifying otherwise inedible plants. Yet, using the cumulative intelligence of many individuals over multiple generations, they develop technologies that successfully exploit principles of aerodynamics, thermodynamics, and chemistry to build sophisticated suites of cultural know-how that allow them to live and thrive in almost any environment.

The breakthrough Henrich presents is not that culture is useful. That’s pretty obvious, intuitively speaking. It’s in the emerging understanding of how humans make culture – and how culture makes humans – in dynamic patterns of feedback and response between our genetic architecture and cultural developments over successive generations. Learning how to process plants and meat, and passing that information down from generation to generation, has worked extraordinary changes on our guts. Domesticating certain ungulates and incorporating their milk into their diets has modified certain population’s ability to metabolize milk well into adulthood. Specialized adaptations allowed humans to move up into otherwise inhospitable latitudes, eventually altering the skin pigmentation of some European populations. The Darwinian framework of gene-culture coevolution allows researchers to move beyond insightful explanation about the plausible roots of human cultural and behavioral variation and get down to the serious business of scientifically explaining these things.

And that is the core point. The revolution here isn’t descriptive, it’s explanatory. Placing our understanding of cultural change in a comprehensive, unified Darwinian framework has moved the study of human behavior forward in a way that other, similarly minded attempts have so far failed to achieve. As more and more researchers across the social sciences – from psychology and sociology to economics and anthropology – come to appreciate and accept the utility of the Darwinian perspective, these fields (particularly anthropology) are beginning to move out of the aimless shadows of what Thomas Kuhn called pre-paradigmatic science.

The reasons for this are simple: the more researchers who work within a coherent, mutually intelligible framework, the greater a field’s capacity for real scientific progress. This is because science itself is something of a Darwinian process. It works through patterns of competition and cooperation among individual researchers (and research groups), who collaborate on complex problems and criticize each other’s work where it falls short of established criteria. This process doesn’t work very well if everyone is working under an entirely different framework – Marxist anthropologists can’t add much to the discussion of Darwinian approaches because they lack both the specialized knowledge and the shared values needed to make sense of and properly evaluate Darwinian work (and vice versa).

In this line, the work of Henrich and other evolutionarily minded social scientists has been immensely beneficial, forging as it has a deeper, broader understanding of the roots of human behavior. And there’s a compelling case to be made that the growing popularity of this theoretical framework isn’t some intellectual fad. Rather, it’s a product of people who share similar goals (to explain things) and similar standards for judging how well those aims have been met (internal coherence, experimental and observational evidence, falsifiability) responding to relevant evidence. The array of approaches couched under the wider framework of gene-culture coevolution just seem to work.

Henrich’s synthesis of this research is among the best that I have read, carefully explaining how evolved psychological traits – like a bias toward watching and mimicking prestigious or successful individuals or a tendency to monitor and enforce social contracts – work in concert with our ever-increasing capacity for high-fidelity information storage and transmission – language evolution, writing technology, printing presses, internet – to create a potentially boundless realm of cultural innovation. Humans are a remarkable species. But, as Henrich argues, our singularity comes not from our innate intelligence – which has been much overblown. Instead, it comes from our ability to put our heads together, creating resilient forms of collective intelligence that allow us to survive – and thrive – practically anywhere we find ourselves.

The Secret of Our Success: How Culture is Driving Human Evolution, Domesticating Our Species, and Making us Smarter – by Joseph Henrich