The only known non-human in which culture and genome have co-evolved.
Cultural practices can diffuse across generations, similar to the way that genes get transmitted from parents to offspring.
Until now, humans have been considered unique in that our culture has driven aspects of our genetic evolution. The best-known examples of this are the genetic changes underlying lactose tolerance that have spread through populations that practice dairy farming.
But culture is not a purely human phenomenon; it appears in pockets throughout nature. It can be seen in songbirds and humpback whales, who acquire their song by listening to others. The use of twigs by chimpanzees to fish for termites in the group can also be regarded as culture, as this skill is passed on to young through observational learning.
Hunting is the cultural forte of killer whales, who have devised sophisticated strategies to capture the prey available in their habitats. Fish-specialists cooperatively herd their prey before attacking, for instance, while some mammal-specialists beach themselves to target seals.
Because killer whales live in stable groups for several decades, mothers have ample time to transfer these specialized hunting skills to their calves.
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Their capacity to teach their young is best exemplified by whales that deliberately strand themselves on beaches, where “mothers have been seen pushing their calves on to the beach apparently to train them. This progresses over several years before the calves are able to hunt in this way themselves,” explained Andrew Foote from Uppsala University in Sweden, lead author of a study published in Nature Communications, in an interview with The Science Explorer.
The study authors identified five distinct killer whale cultural groups and obtained tissue samples from members of each.
Genetic sequences revealed that, despite the fact that the whales had diverged from their common ancestor only a short while ago, in that time, the groups had drifted apart genetically. Cultural evolution appeared to have driven genetic evolution in these killer whales, much like it is known to do in humans.
Some of the clearest indications that the genetic divergences are related to hunting practices were changes that have occurred in genes underlying the breakdown of dietary protein to obtain the amino acid methionine. As Foote explains, “given that mammal-eating killer whales likely get their dietary protein in one or two sittings per day, whereas fish-eating killer whales may be eating more constantly through the day, it may place different selection pressures on this cycle for managing the metabolism of methionine.”
As the cultural groups are now set on separate evolutionary tracks, we may be seeing the first hints of speciation among killer whales. “In our study we found that genes associated with reproduction were diverging rapidly, [which] could be the first steps to some intrinsic barriers to mating,” said Foote.
However, he cautions that any claims about speciation would need to be backed up by a thorough assessment, as changes in species status could have profound conservation implications for killer whales.
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