Once the purview of humans, culture has been observed in all sorts of animals. But are these behaviors merely ephemeral fads or can they shape the genes and traits of future generations?

In Antarctic waters, a group of killer whales makes a wave big enough to knock a seal from its ice floe. Meanwhile, in the North Atlantic, another killer whale group blows bubbles and flashes white bellies to herd a school of herrings into a ball. And in the Crozet Archipelago in the Southern Ocean, still another group charges at seals on a beach, grasps the prey with their teeth, and then backs into the water (1). Some researchers see these as more than curious behaviors or YouTube photo ops: they see cultural mores—introduced into populations and passed to future generations—that can actually affect animals’ fitness.

Killer whales are divided into groups known as ecotypes, with highly specialized diets and hunting traditions passed down over generations. Here, a mammal-eating ecotype in the North Pacific hunts seal. Photograph by David Ellifrit, courtesy of Center for Whale Research.

Killer whales, also known as orcas (Orcinus orca), have a geographic range stretching from the Antarctic to the Arctic. As a species, their diet includes birds, fish, mammals, and reptiles. But as individuals, they typically fall into groups with highly specialized diets and hunting traditions passed down over generations. Increasingly, scientists refer to these learned feeding strategies as culture, roughly defined as information that affects behavior and is passed among individuals and across generations through social learning, such as teaching or imitation (2).

Scientists once placed culture squarely in the human domain. But discoveries in recent decades suggest that a wide range of cultural practices—from foraging tactics and vocal displays to habitat use and play—may influence the lives of other animals as well (3). Studies attribute additional orca behaviors, such as migration routes and song repertoires, to culture (4). Other research suggests that a finch’s song (5), a chimpanzee’s nut cracking (3), and a guppy’s foraging route (6) are all manifestations of culture. Between 2012 and 2014, over 100 research groups published work on animal culture covering 66 species, according to a recent review (7).

Now, scientists are exploring whether culture may shape not only the lives of nonhuman animals but the evolution of a species. “Culture affects animals’ lives and their survival and their fitness,” says the review’s (7) coauthor, behavioral scientist Andrew Whiten of the University of St Andrews in Scotland. “We’ve learned that’s the case to an extent that could hardly have been appreciated half a century ago.” Based on work in whales, dolphins, and birds, some researchers contend that animal culture is likely a common mechanism underlying animal evolution. But testing this hypothesis remains a monumental challenge.

Riding a Cultural Wave Animal populations essentially have two streams of information, genetic and cultural, explains ecologist and whale researcher Hal Whitehead of Dalhousie University in Canada. In the case of the cultural stream, he says, “things are being learned, sometimes from the mother, possibly from the father, as well as from peers and unrelated adults.” Whitehead and others want to understand how these streams interact. Lactose tolerance in humans is a classic example. Studies suggest that adult production of lactase—the enzyme necessary for digesting the sugar lactose in milk—coevolved with the cultural practice of dairy farming in Europe in the last 10,000 years (8). Showing that culture can influence the distribution of genes in an animal population would confirm its role as an evolutionary driver, and Whitehead believes he may have found evidence for exactly that. In the 1990s, Whitehead observed that matrilineal whale species—whose daughters stick with their mothers for life—have low genetic diversity of mitochondrial DNA (9). He coined the term “cultural hitchhiking” to explain how this pattern might emerge. In these species, cultures are passed from mothers to offspring. If a cultural behavior increases a descendant’s chances of survival and reproduction, then this behavior would persist and become more common in the population. The maternal line’s particular mitochondrial DNA haplotype, which also passes directly from mother to offspring, would simultaneously become more common. “The culture is driving and the gene is riding along,” says Whitehead. “There is no particular functional linkage between them.” Whitehead demonstrated through computer models that cultural hitchhiking is a plausible explanation for reduced genetic diversity in matrilineal whale species. Cultural hitchhiking, it seems, is also at work in a population of bottlenose dolphins in western Shark Bay, Western Australia, according to research by evolutionary geneticist Michael Krützen of the University of Zurich (10). In this population, some dolphins carry sponges on their rostrums, most likely for protection as they probe the rough seafloor for fish that they otherwise couldn’t reach (11). This behavior is passed from mothers to offspring through social learning and all “sponging” dolphins in the population share the same mitochondrial haplotype. Because the sponging dolphins primarily inhabit a deep channel where the sponges occur, this culture appears to affect the fine-scale geographic distribution of the mitochondrial genes. “What is really exciting here is that the cultural practice of sponging has led to a change in the genetic make-up of the population when you look at mitochondrial DNA,” says Krützen.

An Evolutionary Force Longstanding ecological and evolutionary theories suggest that culture could also more directly affect the evolution of traits, and even the making of species. Animal populations evolve through natural selection when a heritable trait, like beak size or fur color, varies and different versions of the trait allow some individuals to survive and reproduce more than others. Animal culture has the potential to affect this process in a number of ways, says Whiten. For one, cultural innovations, such as tools or predator-avoidance tactics, could increase an animal’s survival and reproduction, buffering them against some selection pressures. But culture could also enable animals to colonize regions they otherwise couldn’t, exposing them to new selection pressures, such as novel temperatures, predators, or food sources. And culture could generate selection for animals to be better suited to a cultural behavior through physical changes, such as stronger arms for more powerful hammering, or cognitive ones, such as the ability to learn tool use by mirroring others. “And that, of course, may affect the evolution of the brain to match,” says Whiten. Furthermore, cultural differences, such as birdsong or migration patterns, could prevent groups from mating together, which could help maintain or even generate new species. Or anyway, those are the working theories. Finding definitive evidence is a tricky prospect, though recent research in whales and birds offers some substantive support. Scientists refer to the many orca groups with distinct hunting strategies as ecotypes, subsets of a species that occupy unique ecological niches. New genomics technologies allow researchers to search for evolutionary consequences of these various hunting cultures. “We came into the genomics era and really wanted to see whether these cultural traditions in killer whales led to enough of a long-term selection pressure that you would actually see changes in the genome,” says evolutionary biologist Andrew Foote of Bangor University in the United Kingdom. Foote and colleagues sequenced the genomes of 48 orcas across 5 ecotypes to identify whether the groups were truly genetically isolated, and whether their different cultures were associated with unique genomic changes (1). The sample included one mammal-eating and one salmon-eating ecotype from the North Pacific, and one mammal-eating, one penguin-eating, and one Antarctic toothfish-eating ecotype from the Antarctic. The researchers found that the groups were genetically distinct. “What is really surprising is just how differentiated the ones that live in the same area are,” says Foote. “The two North Pacific ones are really different genetically even though there is overlap in their range.” Foote estimated that these ecotypes began diverging within the last 250,000 years. He traced some of the genetic differences among groups to gene variants possibly associated with adaptation to the hunting traditions of each ecotype, and the unique geographic regions those ecotypes colonized. For example, the two mammal-eating ecotypes were each associated with gene variants that play key roles in regulating the metabolism of methionine, an essential amino acid that mammal eaters consume in a boom–bust cycle with influxes following each kill. And the ecotypes that live in the extreme cold of the Antarctic were associated with gene variants involved in the development of adipose tissue, which could protect individuals from the frigid climate. Foote doesn’t believe the cultural barrier between orca ecotypes is long-lasting enough to divide groups into different species altogether. “They probably radiate and collapse and radiate and collapse,” he says. “Maybe one or two might escape that process and go on to become fully fledged species. But looking at what we know now, knowing that they have a relatively recent common ancestor, it would suggest that [splitting into species] never happened in the past.” For birds in the tanager family, like this magpie tanager (Cissopis leveriana) in Brazil’s Itatiaia National Park, song is a cultural trait that must be learned. Song evolves faster in this family than in the ovenbird family, whose species have innate song. Image courtesy of Daniel J. Field (University of Bath, Bath, United Kingdom).

Speciation and Song Birdsong, often used to identify mates, offers another robust means for probing culture’s impact on speciation and animal evolution. For some bird species, song is innate. For others, it’s essentially cultural, a trait that must be learned. In both cases, song evolves over time as it passes through generations. Evolutionary biologist Elizabeth Derryberry of the University of Tennessee, Knoxville, and Nicholas Mason, a doctoral candidate in ecology and evolutionary biology at Cornell University, studied two families of birds: the tanagers (Thraupidae) that learn song and the ovenbirds (Furnariidae) that are innate singers (12). What they found suggests that culture could play a sizeable role. Derryberry and Mason analyzed nearly 4,500 song recordings across nearly 600 species within these families. For each recording, they measured eight vocal characters, including maximum volume, range of pitch, and length. By studying differences in these characters between species in the same family, the researchers estimated how quickly song evolved in different branches of the family tree. If song differed greatly between closely related species, for example, that would suggest a fast rate of song evolution. For each family, they merged this song dataset with a genetic one that showed rates of speciation; the idea was to identify any connection between the rates of song change and species divisions. Derryberry and Mason found that when the rate of song evolution sped up in a branch of a family tree, so too did the rate of speciation. But song evolved 1.4 times faster in the tanager family, with cultural transmission of song, than in the ovenbird family, with innate song. Culture, therefore, might actually ramp up the pace of speciation. Derryberry and Mason (12) acknowledge that they don’t know whether bird song evolution drives speciation or vice versa. In one scenario, bird song could diverge first, which would prevent individuals with different songs from mating together, setting their lineages on the path to becoming distinct species. Alternatively, the species could diverge first by some other mechanism, which would create strong natural selection for song divergence to follow. If song evolution comes first, then the faster bird song evolves, the more rapidly species diverge. “My inkling is that rapid evolution of birdsong could contribute to speciation,” says Mason. “At the scale we are looking at, we look at patterns, so interpreting process becomes tricky.” A separate, long-term study may offer insight into the speciation cause and effect. For four decades, evolutionary biologists Peter and Rosemary Grant of Princeton University carefully tracked the survival, mating, and reproduction success of about 12,000 individual birds in species of Darwin’s finches on the island of Daphne Major in the Galápagos (5). In these species, which belong to the tanager family included in Mason’s study, offspring learn song from their fathers. In 1981, a male bird from a nearby island arrived on Daphne Major singing a song the Grants had never heard. Genetic analyses (conducted decades later with microsatellite data) suggested that it was possibly a hybrid of the medium ground finch (Geospiza fortis) and the cactus finch (Geospiza scandens), two species that were also found on Daphne Major. But this bird, which the Grants call “Big Bird,” was much larger than the parent species. Big Bird survived for 13 years in his new home and found six mates: the first three hybrids like himself, the last three all medium ground finches. Together with one of the medium ground finches, Big Bird produced offspring that bred only with one another, resulting in the beginnings of an incipient species that the Grants have now followed through six generations. “My inkling is that rapid evolution of birdsong could contribute to speciation.”—Nicholas Mason The bird’s unique song passed on through generations helped members of his lineage recognize one another as potential mates. “It’s very important that it’s had cultural transmission of song,” says Rosemary Grant. There is no agreed upon standard for how many generations a lineage must remain reproductively isolated before it can be called a new species, so the Grants maintain only that the Big Bird lineage is a species in the making.