Evidence is growing that culture is an important determinant of the behavior of whales and dolphins. Among the many definitions of culture, one that is commonly used by evolutionary biologists and is useful when studying the phenomenon in whales and dolphins, is behavioral variation between sets of animals maintained and transmitted by social learning. There are two principal approaches to the study of nonhuman culture. Because some scientists will only ascribe culture to a behavioral pattern if it can be proved to be transmitted between animals by imitation or teaching, they investigate transmission mechanisms experimentally. Others, who use a broader definition of culture encompassing any form of social learning (not just imitation or teaching), look for patterns of behavioral variation in wild populations that cannot be explained by either genetic factors or environmental differences plus individual learning. This has been called the “ethnographic” approach to the study of culture.
The common bottlenose dolphin (Tursiops truncatus) has been shown experimentally to posses sophisticated social learning abilities, including vocal and motor imitation, but these have not been closely tied to observed patterns of behavior in the wild. Although social learning of other cetacean species has not been studied experimentally, there is observational evidence for imitation and teaching in some other whales and dolphins, especially killer whales (Orcinus orca).
Taking the second, ethnographic, approach, there is good evidence for cultural transmission in several cetacean species. Most notably, the complex and stable vocal (call dialects) and behavioral (foraging patterns and techniques) cultures of sym-patric groups of killer whales have no known parallel outside humans and represent an independent evolution of cultural faculties. Although evidence is less firm, sperm whales (Phy-seter macrocephalus) also seem to have important group-based cultures, which include distinctive dialects. Perhaps most remarkable of all cetacean cultures is the song of male humpback whales (Megaptera novaeangliae). All males on any breeding ground sing nearly the same song, but it evolves over periods of months and years. This evolution is usually gradual, but over a 2-year period, the males off eastern Australia unanimously adopted the radically different western Australian song, which they had heard from a few itinerant males.
Several factors may be implicated in the apparent importance of cultural transmission of behavior among cetaceans. Long lives, prolonged parental care, and substantial cognitive abilities are often associated with the evolution of cultural faculties, and these are generally characteristic of cetaceans, as well as other cultural animals, such as primates and some birds. The wide movements of cetaceans and the greater variability of the marine biotic environment relative to that on land, as well as the stable matrilineal social groups of some species, are potentially important factors in the evolution of some of the more unusual aspects of cetacean culture.
Culture can affect the evolution of other aspects of the lives of animals. There have been a number of suggestions for gene-culture coevolution in cetaceans, and culture may be implicated in some of their unusual behavioral and life history traits. For instance, it has been proposed that the separation between “resident,” fish-feeding and “transient,” mammal-feeding forms of killer whales (which now show morphological and genetic differences) was originally driven by culture. Another suggestion is that cultural selection may have caused the low diversity of mitochondrial genes found in matrilineal whales, as these genes and beneficial cultural traits may have been inherited together by daughters from their mothers. Culture may also be implicated in mass strandings, as well as in the pronounced menopause shown by killer and pilot whale females (which is known only from humans among noncetaceans).
The focused study of culture in whales and dolphins is just beginning. Despite denials from those who demand experimental proof of imitation or teaching before attributing culture, there are strong indications that, in common with humans and chimpanzees, much of the behavioral repertoire of many cetaceans is learned socially and constitutes culture. Culture may also be an important attribute of other marine mammals, with the foraging techniques of sea otters (Enhydra lutris) perhaps forming the clearest example.
