Coevolving Genes and Culture
- Taxa: Cetaceans
- Topics: Cultural Evolution
Hal Whitehead is advancing a perspective he and Luke Rendell developed in The Cultural Lives of Whales and Dolphins (2015). After demonstrating from many angles the relevance of culture to understanding cetaceans, now he is directing that perspective to rethinking evolution. He aims to contribute to the developing case for revising the “modern synthesis” (fusing Darwin with Mendel) by way of an “extended evolutionary synthesis,” which sees inheritance operating in multiple registers (epigenetic, physiological, ecological, social and cultural). For social theory, the key point in this view is that culture has the capacity to shape evolution, which should prompt a rethinking of the founding theoretical insistence on keeping the two apart. Gene-culture coevolution is the larger speculative frame, and its dynamics are being tentatively worked out in humans. Whitehead’s basic point is that this frame ought to encompass nonhumans, starting with whales and dolphins. Simply, they’re simpler: “simple cultural systems…could accentuate the effects of culture on genes or make them more discernible.” The case for culture shaping genes and biology may advance more rapidly by focusing on nonhumans.
Cetaceans, generally, are a great choice because their social life features evidence “for cultural transmission in song, migrations, foraging, behavior, social conventions, cooperative associations with humans, and play.” Most importantly, culture seems to play a potential role in speciation, or at least its incipient form, ecotypes—a genetically distinct, geographically located grouping within a species, adapted to specific environmental conditions. This requires great stability in the cultural form, which Whitehead sees indicated in whale matrilineal social systems, wherein calves learn migration routes, dialects, and foraging strategies. In this paper, he reviews, “four general hypotheses for gene–culture coevolution in whales and dolphins: (i) that culture has led to incipient speciation of killer whale ecotypes; (ii) that culture has driven the evolution of functional genes in killer whales; (iii) that low levels of mtDNA diversity in five species of matrilineal odontocete result from cultural hitchhiking; and (iv) that geographical patterns of mtDNA result from cultural behavior.” The case of killer whales is central because this diverse species features at least six ecotypes, ranging across the North Pacific, North Atlantic and Arctic. Ecotypes arise from some ecological source of divergent selection linked via some mechanism to reproductive isolation. Whitehead observes, “The killer whale scenario is especially interesting because culture seems to play a key role in all three components”— different matrilineal social units have distinctive lifeways. Foraging tactics are acquired socially within these units; as they “become more efficient through cultural selection, they will tend to become more specialized, so that matrilines, or groups of socially connected matrilines, develop new ways of life. These matrilines are thought to be the progenitors of the ecotypes.”
An interesting aspect of all this is the work entailed of thinking in parallel with humans—extending the case for cultural influences on gene distribution. Much as with humans, “the geographical distribution of cetacean genes has a strong cultural imprint,” one that might be far more legible: “the clear phylogenetic and cultural divisions between killer whale ecotypes make it easier, in some respects, to pin down gene–culture coevolution in these species than in the messier trajectory of human evolutionary history.” The case might be even more intriguing with whales and dolphins because this distribution does not seem to be geographically determined—as with mountain chains or seas, for humans—and may be the product of cultural boundary work. Whitehead reports that some former summering of baleen whales remain empty, an artifact of over-fishing, while adjacent ones are actively occupied. “This distinction has been maintained over several thousand generations even though there are no physical barriers between the summering grounds and the migration routes and wintering grounds of the two populations, where the animals mate, overlap so that there is mating between them.” These distinctions may just be the result of “social learning” or they may additionally reflect boundary work maintenance by these whales—in teaching their calves where to go they may also be instructing them on where not too; the latter involves cultural interpretation of belonging and difference. As well, it entails doing more than documenting analogous interplays of culture and genes in humans and nonhumans, but also adopting and applying a more fulsome understanding of how this dynamic is analyzed in humans.
But this is more than a matter of tapping cultural theory; ethnographic techniques also are potentially quite relevant. Whiten comments that, though our understanding of gene-culture evolution in whales and dolphins is pretty good, “in contrast, studies of cetacean social structure and culture are naturally slow and painstaking and are not getting any cheaper.” But they’re what’s required to advance this thinking in parallel: “the socio-cultural side needs innovation, commitment, and investment.” Is there an ethnographer ready to go?
Hal Whitehead, “Gene–Culture Coevolution in Whales and Dolphins,” PNAS 114, no. 30: 7814–21, https://doi.org/10.1073/pnas.1620736114.
Whales and dolphins (Cetacea) have excellent social learning skills as well as a long and strong mother–calf bond. These features produce stable cultures, and, in some species, sympatric groups with different cultures. There is evidence and speculation that this cultural transmission of behavior has affected gene distributions. Culture seems to have driven killer whales into distinct ecotypes, which may be incipient species or subspecies. There are ecotype-specific signals of selection in functional genes that correspond to cultural foraging behavior and habitat use by the different ecotypes. The five species of whale with matrilineal social systems have remarkably low diversity of mtDNA. Cultural hitchhiking, the transmission of functionally neutral genes in parallel with selective cultural traits, is a plausible hypothesis for this low diversity, especially in sperm whales. In killer whales the ecotype divisions, together with founding bottlenecks, selection, and cultural hitchhiking, likely explain the low mtDNA diversity. Several cetacean species show habitat-specific distributions of mtDNA haplotypes, probably the result of mother–offspring cultural transmission of migration routes or destinations. In bottlenose dolphins, remarkable small-scale differences in haplotype distribution result from maternal cultural transmission of foraging methods, and large-scale redistributions of sperm whale cultural clans in the Pacific have likely changed mitochondrial genetic geography. With the acceleration of genomics new results should come fast, but understanding gene–culture coevolution will be hampered by the measured pace of research on the socio-cultural side of cetacean biology.