Non-chimp Animal Culture

By Bob Grant

Chimpanzees aren't the only animals that show glimmers of culture. Song birds, crows, whales, and even rats appear to behave in ways that approximate social custom or tradition sharing. Two recent examples of putative animal cultures come from apes in Southeast Asia, and a population of marine mammals that makes its home off the west coast of Australia.

In Shark Bay, some bottlenose dolphins break live sponges from the seafloor, shove them onto their slender beaks, and probe sediments for crustaceans and fish with the protection of this natural face mask. Though scientists first observed "sponging" in Shark Bay's bottlenose dolphins about 20 years ago, Michael Krtzen, a molecular ecologist and anthropologist at the University of Zurich, and colleagues suggested in a 2005 paper,¹ that sponging is a socially learned behavior and likely not the result of genetic inheritance.

"We were the first to consider extensive genetic data to actually exclude genetic explanations for the behavior," says Krtzen. He and his team took tissue samples from 185 dolphins in Shark Bay, thirteen of which were known adult spongers. Only one of these spongers was male. The researchers genotyped each individual for 12 bi-parentally inherited microsatellite loci and sequenced a maternally inherited control region of mitochondrial DNA for each dolphin.

They found, by considering the mtDNA profiles, that the spongers shared a recent common female ancestor, making them closely related and all part of the same matriline. The researchers considered ten different scenarios, including sex or mitochondrial chromosome linkage, in which the behavior is mediated by a single gene or several closely linked genes; they discounted all of them because their observations of sponging failed to match expected distributions of the behavior within the population.

Because both spongers and nonspongers forage in the same deep-water channels, Krtzen's team also largely dismissed ecological variation as a reason for why some of the Shark Bay dolphins sponge and some don't. This led Krtzen and his team to conclude that the female bottlenose dolphins were learning to sponge from their mothers and passing along this skill to their own daughters.

That conclusion was the subject of some discussion between the coauthors of a paper eventually published in PNAS, says coauthor Janet Mann, a Georgetown University biologist and psychologist. And since then, research by Mann and others has suggested that ecological factors, such as water depth, season, and marine sponge distribution, could play a part in determining the dolphins that sponge and those that don't.²

"I do agree that social learning does have to be involved in the sponge carrying," Mann says, "but the environment is clearly important. I think that the PNAS paper dismissed the ecological contribution more than it should have." Krtzen acknowledges that ecology might play a more important role than previously assumed, but says he's "still utterly convinced that [sponging] is an example of social learning."

Similar to chimps in Africa, wild orangutan populations in Borneo and Sumatra have developed regionally variable behavioral patterns that could potentially be used to differentiate one orangutan group from another (see Infographic: Primate customs). Carel van Schaik and an international team of researchers identified 19 different orangutan behaviors in a 2003 Science paper,³ calling them "very likely cultural variants." These behaviors include the use of foraging tools and seemingly arbitrary behaviors that may signal an individual's intentions to other orangutans, with the presence of these behaviors differing across the orangutan's ever-shrinking range.

Pointing to genetic and ecological similarities that exist between some orangutan populations and their tropical habitats, van Schaik and his team identify social transmission as the most likely vehicle for the spread and maintenance of these behaviors. They even suggest that material culture in orangutans places the ancient root of human culture farther back in evolutionary history: "The presence in orangutans of humanlike skill (material) culture pushes back its origin in the hominoid lineage to about 14 million years ago, when the orangutan and African ape clades last shared a common ancestor."