The authors have tackled the important question of how and why genetic effects are often obscured by effects of cumulative culture, applying a dual inheritance framework. They attribute this deficit in part to the WEIRD (western, educated, industrialized, rich, and democratic) sampling problem where western subjects are considered to be representative of our species. They then seek the cultural “generative processes that bring such complex objects and conditions into existence” (sect. 5.1, para. 1) proposing that answers can be reached through a cultural evolutionary framework. Fortunately, the WEIRD problem has never plagued anthropologists whose goal has always been to document cultural systems so that other societies do not appear weird. What can we learn from the vast body of ethnography collected over centuries to further our understanding of the dynamics of cultural clusters?

The authors take a diffusionist perspective with the unit of selection being cultural group selection. Innovations are proposed to spread by conformist biases, learning from successful others, and punishing norm violators to produce cultural clusters. However, this approach sidesteps the ethnographically documented agency of individuals and internal complexity of social groups which so drives cultural evolution. At least three forces of selection acting upon agents need to be considered to understand how cumulative culture and cultural clusters are generated and evolve. The first is adaptation to the natural or culturally altered environment. The second is social selection (Hrdy, Reference Hrdy2016; Nesse, Reference Nesse2007; West-Eberhard, Reference West-Eberhard1979), a frontline selection pressure that partially determines with whom one marries, cooperates in child rearing, and exchanges, as well as how many supporters and opponents one has over the life cycle. It has everything to do with shaping our psychology and masking or unmasking estimates of genetic heritability. Take the skin cancer example. The use of ochre and other means for sun protection appears to over 100,000 years old (Lüpke et al., Reference Lüpke, Stenzel, Cabalzar, Chacon, da Cruz, Franchetto and Storto2020). Today, the Himba women in Namibia use fat and ochre to maintain sexually attractive skin; men do not. The heritability of cancer for one gender only will be masked (Summers et al., Reference Summers, Lategan, Rifkin, d'Errico and Garcia-Morenond).

Social selection appears to be responsible for our better angels and devils. Boehm (Reference Boehm2012) and Wrangham (Reference Wrangham2019) have proposed that it was the key process for our self-domestication. Nesse (Reference Nesse2016) has argued that only social selection can explain our extreme pro-sociality. Moreover, social selection is a strong force behind the universal human obsession with reputation. It can lead to oppression, exploitation, and manipulation, creating segments within societies. Knowing who benefits from innovations is essential for understanding the internal configurations of cultural clusters. Finally, there is cultural group selection for which evidence remains debated (commentary, Richerson et al., Reference Richerson, Baldini, Bell, Demps, Frost, Hillis and Zefferman2016). The impermeability of barriers created by mutually unintelligible languages or cultural clusters that would facilitate cultural group selection is often over-estimated. As Barth (Reference Barth1998) has proposed, ethnic distinctions do not depend on the absence of social interaction and acceptance, but on the contrary, are often the very foundations on which embracing social systems are built. Open boundaries are evidenced by the fact that many people in traditional and modern societies speak three to four languages, a trend pronounced in South America and West Africa (Lüpke et al., Reference Lüpke, Stenzel, Cabalzar, Chacon, da Cruz, Franchetto and Storto2020).

Cumulative culture comes in single tools or traits, complex subsistence strategies, and entire cultural institutions. The level of selection operant on different features of cumulative culture profoundly structures their import for obscuring genetic heritage. Many traits that distinguish social clusters are functionally equivalent and of purely symbolic value; they are products of social selection to define clusters of people who share obligations to one another. Examples from Highland Papua New Guinea abound as linguistic and dialect groups distinguish themselves by signature styles of body decoration and ceremonial dress. Some groups choose other means: The Etoro, Onabasulu, and Kakuli of the Bosavi area differentiate by customs in male initiations. Growth and maturation are contingent on insemination with the semen of elders; how semen is transmitted through different forms of intercourse is believed to produce culturally distinct beings (Kelly, Reference Kelly1974). Such traits marking identity stand fast at boundaries regardless of rates of interaction.

Traits that mark identity obscure many essential commonalities across cultures. Complex cultural packages that confer strong selective advantages spread rapidly across boundaries allowing people from distinct linguistic and cultural groups to share many behaviors and adaptations. I will give three examples. (1) Sweet potatoes, introduced to Highland Papua New Guinea cultures some 400 years ago, released constraints on agricultural production and spread widely in response to environmental pressures long before first contact with Europeans (Ballard, Brown, Bourke, & Harwood, Reference Ballard, Brown, Bourke and Harwood2005). Utilization of the new crop created homogeneity in subsistence practices and pig husbandry across vast areas, similarities which could be obscured by linguistic differences and expressions of cultural identity. (2) Among the Enga, bachelors' cults to discipline and educate cohorts of youths arose before European contact in some clans of central Enga under conditions of intense competition in trade, ceremonial exchange, and warfare. Big-men along trade routes identified successful clans from whom to purchase the transformative rites to improve clan fortune, while bachelors raised the wealth and went on journeys to do so (Wiessner & Tumu, Reference Wiessner and Tumu1998). Within two to three generations, bachelors' cults were adopted by 500 or more clans in the five dialect groups of Enga, fostering group loyalty and masking individualistic agendas. Meanwhile influential big-men exerted pressures to proclaim their enterprising sons as marriageable years before others to jump start their polygynous careers, creating reproductive inequalities. (3) Intraclan institutions applying restorative justice were adopted across linguistic groups in most Highland societies where intergroup competition was fierce. Social selection drove their development to bring potentially productive transgressors back into community, compensate for harm done, restore cooperation, and avoid the grudging conformity that ensues from punishment. Restorative measures fostered tolerance, openness, and innovation (Wiessner, Reference Wiessner2020).

The many selection pressures that operate on agents who steer the course of cultural evolution must be considered to understand how cultural heterogeneity and homogeneity are generated and whether their content is significant for masking or unmasking genetic inheritance. For this purpose, the ethnographic record is most valuable.