Henrich’s The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter

When humans compete against chimps in tests of working memory, information processing or strategic play, chimps often come out on top. If you briefly flash 10 digits on a screen before covering them up, a trained chimp will often better identify the order in which the numbers appeared (see here). Have us play matching pennies, and the chimp can converge on the predicted (Nash equilibrium) result faster than the slow to adapt humans.

So given humans don’t appear to dominate chimps in raw brain power (I’ll leave contesting this particular fact until another day), what can explain the ecological dominance of humans?

Joe Henrich’s answer to this question, laid out in The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter, is that humans are superior learning machines. Once there is an accumulated stock of products of cultural evolution – fire, cutting tools, clothing, hunting tools and so on – natural selection favoured those who were better cultural learners. Natural selection shaped us to be a cultural species, as Henrich explains:

The central argument in this book is that relatively early in our species’ evolutionary history, perhaps around the origin of our genus (Homo) about 2 million years ago … cultural evolution became the primary driver of our species genetic evolution. The interaction between cultural and genetic evolution generated a process that can be described as autocatalytic, meaning that it produces the fuel that propels it. Once cultural information began to accumulate and produce cultural adaptations, the main selection pressure on genes revolved around improving our psychological abilities to acquire, store, process, and organize the array of fitness-enhancing skills and practices that became increasingly available in the minds of the others in one’s group. As genetic evolution improved our brains and abilities for learning from others, cultural evolution spontaneously generated more and better cultural adaptations, which kept the pressure on for brains that were better at acquiring and storing this cultural information.

The products of cultural evolution make us (in a sense) smarter. We receive a huge cultural download when growing up, from a base 10 counting system, to a large vocabulary allowing us to communicate complex concepts, to the ability to read and write, not to mention the knowhow to survive. Henrich argues that we don’t have all these tools because we are smart – we are smart because we have these tools. These cultural downloads can’t be devised in a few years by a few smart people. They comprise packages of adaptations developed over generations.

As one illustration of this point, Henrich produces a model where people can be either geniuses who produce more ideas, or social with more friends. Parameterise the model right and social groups end up much “smarter” with a larger stock of ideas. It is better to be able to learn and have more friends to learn from (again, within certain parameters) than have a fewer number of smarter friends. The natural extension of this is that larger populations will have more complex technologies (as Michael Kremer and others have argued – although see my extension on the evolving capacity to generate ideas).

One interesting feature of these cultural adaptations is that the bearers don’t necessarily understand how they work. They simply know how to effectively use them. An example Henrich draws on are food processing techniques developed over generations to remove toxins from otherwise inedible plants. People need, to a degree, to learn on faith. An unwillingness to learn can kill.

Take the consumption of unprocessed manioc (cassava), which can cause cyanide poisoning. South American groups that have consumed it for generations have developed multi-stage processes involving grating, scraping, separating, washing, boiling and waiting. Absent those, the poisoning emerges slowly after years of eating. Given the non-obvious nature of the negative outcomes and link between the practices and outcomes, the development of processing techniques is a long process.

When manioc was transported from South America to West Africa by the Portuguese, minus the cultural protocols, the result has been hundreds of years of cyanide poisoning. The problem that remains today. Some African groups have evolved processing techniques to remove the cyanide, but these are only slowly spreading.

Beyond the natural selection for learning ability, Henrich touches on a few other genetic and biological angles. One of the more interesting is the idea that gene-culture co-evolution can lead to non-genetic biological adaptations. The culture we are exposed to shapes our minds during development, leading to taxi drivers in London having a larger hippocampus, or people from different cultures having different perceptual ability when it comes to judging relative or absolute size. Growing up in different cultures also alters fairness motivations, patience, response to honour threats and so on.

Henrich is right to point out that his argument does not imply that seeing differences between groups implies cultural differences. They could be genetic, and different cultures over time could have moulded group differences. That said, Henrich also suggests genes play a tiny role, although it’s not a position brimming with analysis. As an example, he points out the high levels of violence among Scottish immigrants in the US Deep South who transported and retained an honour culture, compared to the low levels of violence in Scotland itself (or New England where there were also Scottish immigrants), without investing much effort in exploring other possibilities.

Henrich briefly addresses some of the competing hypotheses for why we evolved large brains and developed a the theory of mind (the ability to infer others’ goals). For example the Machiavellian hypothesis posits that our brains evolved to outthink each other in strategic competition. As Henrich notes, possessing a theory of mind can also lead to us more effectively copy and learn from them (the cultural intelligence hypothesis). Successful Machiavellian’s must be good cultural learners – you need to learn the rules before you can bend them.

Since the release of Henrich’s book, I have seen little response from the Stephen Pinker’s and evolutionary psychologists of the world, and I am looking forward to some critiques of Henrich’s argument.

So let me pose a few questions. As a start, until the last few hundred years, most of the world’s population didn’t use a base 10 counting system, couldn’t write and so on. Small scale societies might have a vocabulary of 3,000 to 5,000 words, compared to the 40,000 to 60,000 words held in the mind of the typical American 17-year old. The cultural download has shifted from something that could be passed on in a few years to something that takes a couple of decades of solid learning. Why did humans have so much latent capacity to increase the size of the cultural download? Was that latent capacity possibly generated by other mechanisms? Or has there been strong selection to continue to increase the stock of cultural knowledge we can hold?

Second, is there any modern evidence for the success of those who have better cultural learning abilities? We have evidence the higher reproductive success of those who kill in battle (see Napoleon Chagnon’s work) or those with higher income. What would an equivalent study to show the higher reproductive success of better cultural learners look like (assuming selection for that trait is still ongoing)? Or is it superior learning ability that leads to people to have higher success in battle or greater income? And in that case, are we just talking IQ?

Having been reading about cultural evolution for a few years now, I still struggle to grasp the extent to which it is a useful framework.

Partly, this question arises due to the lack of a well-defined cultural evolution framework. The definition of culture is often loose (see Arnold Kling on Henrich’s definition) and it typically varies between cultural evolution proponents. Even once it is defined, what is the evolutionary mechanism? If it is natural selection, what is the unit of selection? And so on.

Then there is the question of whether evolution is the right framework for all the forms of cultural transmission? Are models for the spread of disease a better fit? You will find plenty of discussions of this type of question across the cultural evolution literature, but little convergence.

Contrast cultural evolution with genetic natural selection. In the latter, high fidelity information is transmitted from parent to offspring in particulate form. Cultural transmission (whatever the cultural unit is) is lower-fidelity and can be in multiple directions. For genetic natural selection, selection is at the level of the gene, but the future of a gene and its vessels are typically tightly coupled within a generation. Not so with culture. As a result we shouldn’t expect to see the types of results we see in population/quantitative genetics in the cultural sphere. But can cultural evolution get even close?

You get a flavour of this when you look through the bespoke models produced in Henrich’s past work or, say, the work by Boyd and Richerson. Lot’s of interesting thinking tools and models, but hardly a unified framework.

A feature of the book that I appreciated was that Henrich avoided framing the group-based cultural evolutionary mechanisms he describes as “group selection”, preferring instead to call them “intergroup competition” (the term group selection only appears in the notes). In the cultural evolution space, group selection is a label that tends to be attached to all sorts of dynamics – whether they resemble genetic group selection processes or not – only leading to confusion. Henrich notes at one point that there are five forms of intergroup competition. Perhaps one of these might be described as approaching a group selection mechanism. (See West and friends on this point that in much of the cultural evolution literature, group selection is used to refer to many different things). By avoiding going down this path, Henrich has thankfully not added to the confusion.

One thread that I have rarely seen picked up in discussion of the book (excepting Arnold Kling) is the inherently conservative message that can be taken out of it. A common story through the book is that the bearers of cultural adaptations rarely understand how they work. In that world, one should be wary of replacing existing institutions or frameworks.

When Henrich offers his closing eight “insights”, he also seems to be suggesting we use markets (despite the absence of that world). Don’t design what we believe will work and impose it on all:

Humans are bad at intentionally designing effective institutions and organizations, although I’m hoping that as we get deeper insights into human nature and cultural evolution this can improve. Until then, we should take a page from cultural evolution’s playbook and design “variation and selection systems” that will allow alternative institutions or organizational forms to compete. We can dump the losers, keep the winners, and hopefully gain some general insights during the process.