Uchiyama et al. conclude that “Nothing in behavioral genetics makes sense except in the light of cultural evolution” (sect. 6, para. 3). This claim may seem like an exaggeration, but like Uchiyama et al., I think human genetics cannot be considered without recourse to culture because so many of our behaviors – indeed most of what makes humans unique – do not exist outside of culture. Absent cultural support, not only do we lack skills like reading, arithmetic, and rugby, but also species-typical behaviors like a compositional and productive communication system (i.e., natural language). Absent culture, we can't even feed ourselves! Our digestive system has adapted to cooked food (Wrangham, Reference Wrangham2009) and how many of us would invent de novo control of fire and rediscover cooking? With such behaviors being at the mercy of cultural learning, can we really talk about heritability of a trait without understanding its cultural underpinnings? I will argue that we cannot.

A common way of thinking about environmental effects on heritability is in terms of environmental deprivation that masks genetic potential. For example, a person's height may be stunted by malnutrition preventing them from reaching their “genetic potential” and reducing measured heritability (Perkins, Subramanian, Davey Smith, & Özaltin, Reference Perkins, Subramanian, Davey Smith and Özaltin2016). The intuition is that the person's true potential is being masked. If only they had received the normal amount of nutrition, they would grow to the height their genes prescribe.

But just on the other side of this equation is the unmasking of traits by culture. And here, our intuitions begin to break down. Consider De Moor et al.'s (Reference De Moor, Spector, Cherkas, Falchi, Hottenga, Boomsma and De Geus2007) calculation of a 0.66 heritability of being a UK high school or university athlete. This seems impressive, but what would the calculated heritability be if the study took place in the United Kingdom 500 years ago? Or at a contemporary time, but in a place with no school sports? If the answer is that question doesn't even make sense because there would be no outcome to observe, that is precisely the point. Cultural institutions have created a domain – competitive sports – whose heritability we can measure. But that measurement is necessarily restricted to a particular time and place.

Perhaps, no other human trait has been the subject of more attempts at heritability estimates than intelligence, with estimates running as high as 0.8 (Plomin & Deary, Reference Plomin and Deary2015) leading to the puzzle of “missing heritability” (Feldman & Ramachandran, Reference Feldman and Ramachandran2018). Similarly to Feldman and Ramachandran, Uchiyama et al. argue that the resolution of the puzzle lies in integrating culture. It is worth elaborating on some of the problems with attempts to view intelligence as a culture-free trait.

While the goal of conventional tests is to measure knowledge or ability, the goal of IQ tests is to measure intelligence itself. This is justified by the observation that when people are tested on a variety of cognitive measures: vocabulary, analogies, figuring out what rule a sequences of shapes follow, remembering numbers, the scores are positively correlated. Some people excel more on some tasks than others, but in general, doing well on one means doing well on the others. This so-called positive manifold is reasoned to have a common cause which is g (Ritchie, Reference Ritchie2015). Estimates of heritability of intelligence are estimates of the heritability of g. The problem is that measures of intelligence (IQ tests) are ineluctably cultural products. Heritability of g is therefore necessarily linked to the culture.

There are several objections to the claim that IQ cannot be considered independently of culture. First, it may be argued that although some IQ subtests such as vocabulary are culturally loaded, others such as fluid reasoning are not (Jensen, Reference Jensen1980). A problem with this contention is that more culturally loaded tests show greater heritability than putatively culture-free tasks (Kan, Wicherts, Dolan, & van der Maas, Reference Kan, Wicherts, Dolan and van der Maas2013). The claim that assessments of fluid reasoning are culture free because they are nonverbal is also naïve to the reliance of these tests on culturally learned patterns and symbols (Richardson, Reference Richardson2002; Roebuck & Lupyan, Reference Roebuck and Lupyanunder review; Rosselli & Ardila, Reference Rosselli and Ardila2003).

Second, it may be argued that although any specific IQ test is a product of a specific time and place, the quantity it measures generalizes beyond cultures and time periods. We can make this claim more vivid using a thought experiment. Take 100 modern Americans whose measured adult IQ scores span a wide range and transport them (as infants) to various times and places. Allow them to grow up and be enculturated at their destinations, and then test them on that culture's version of an intelligence test (one having similarly high predictive validity in life outcomes as our IQ tests). If IQ tests measure g, then the person scoring in the top 1% would come out on top regardless of the time and place they were transported to thanks to the preservation of their intelligence-coding genes. The person at the 30th percentile would likewise stay around there. The rank correlation would be preserved. Perhaps it would. But this assumption has zero empirical support and there are good reasons to doubt it.

Consider: for most of human existence, someone with poor wayfinding abilities would be at an extreme disadvantage and likely considered rather unintelligent. Now, they can just use their phones. Variation in wayfinding has become masked and is certainly not something we include in IQ testing. If we did, it might decrease the strength of the positive manifold (Hegarty, Montello, Richardson, Ishikawa, & Lovelace, Reference Hegarty, Montello, Richardson, Ishikawa and Lovelace2006). Conversely, individual differences in logical reasoning, reading, and the ability to sit still for long periods would be of little consequence in times past, but have now been unmasked by the demands of modern culture. The former two skills are explicitly measured by intelligence testing; the latter is an implicit prerequisite (DeDeo, Reference DeDeo2018; Stephenson, Reference Stephenson2012). Is it not hubris to think that figuring out sequences of shapes – a mainstay of modern IQ tests – is a proper measure of “general intelligence” while wayfinding is a mere specialized skill? It is time to recognize that culture is not a peripheral appendage on the leash of our genes (pace Wilson, Reference Wilson2004), but is the vehicle that makes possible many of our most important behaviors.