We disagree with two of Rendell and Whitehead's assertions. Culture may be an ancestral characteristic of terrestrial cetacean ancestors; not derived via marine variability, modern cetacean mobility, or any living cetacean social structure. Furthermore, evidence for vocal behavior as culture, social stability, and cognitive ability, is richer in birds than Rendell and Whitehead portray and comparable to that of cetaceans and primates.

The use of anecdotes is not a viable research strategy to study animal culture. Social learning processes can often be documented with careful quantitative analyses of observational data. Unfortunately, suggestions that killer whales engage in teaching are entirely based on subjective interpretations of qualitative observations. Thus, “evidence” of teaching in killer whales cannot be used to argue for the occurrence of culture in marine mammals.

Rendell and Whitehead have drawn attention to some striking cetacean behaviour patterns. However, the claims for “culture” are premature. Weak examples of cetacean social learning do not, in sum, provide strong evidence for culture. Other terms, such as social learning, vocal learning, imitation, and tradition may be applied in some cases without resorting to more complex and controversial terms.

The target article provides stimulating evidence for culture in cetaceans but does not provide a coherent theoretical framework. We argue that a complex, adaptive systems approach not only can provide such a framework but also can contribute advanced data analysis and simulation methods. For humpback whale songs, we suggest the framework of “small-world networks” to model the observed spatio-temporal dynamics.

We agree with Rendell and Whitehead that cetaceans acquire knowledge from caretakers and peers, and that a clear understanding of this process can provide insight into the evolution of mammalian cognition. The passive observational methods they advocate, however, are inadequate for determining what cetaceans know. Only by experimentally investigating the cognition of cetaceans can we hope to understand what they learn through social interactions.

Results of genetic analyses show that social groups of female and immature sperm whales are comprised of multiple matrilines as evidenced by the presence of multiple mitochondrial (maternally inherited) control region haplotypes. These data suggest: (1) a social environment in which the transmission of cultural information, such as vocal dialects, is more likely to be horizontal or oblique rather than strictly vertical (mother-offspring) and (2) lead us to question the data presented to support gene-culture coevolution.

Rendall and Whitehead overstate the weak evidence for social learning in cetaceans as a group, including the current evidence for vocal learning in killer whales. Ethnographic techniques exist to test genetic explanations of killer whale calling behavior, and additional captive experiments are feasible. Without such tests, descriptions of learning could be considered pseudo-scientific, ad hoc auxiliary assumptions of an untested theory.

The types of cetacean cultural behavior patterns described (primarily food-related and communication-related) reflect a very different research focus than that found in primatology, where dietary variation and food processing is emphasized and other potentially “cultural” patterns have (until recently) been relatively neglected. The lack of behavioral research in all but a few cetacean species is also notable, as it mirrors a bias in primatology towards only a few genera.

Defining culture as social learning means that culture is present in many birds and mammals, suggesting that cetacean culture is not so special and does not require special explanation. Contrary to their own claims, Rendell and Whitehead present culture as having variant forms in different species, and these forms seem inconsistently applied and compared across species.

Monkeys and apes, inhabiting variable environments and subjected to K-selection, exhibit cultural behavior transmitted horizontally and vertically, like cetaceans. Behaviors enhancing better health and nutrition, predator avoidance, or mate selection, can affect differential reproduction.Furthermore, dominance hierarchies and social status not only affect the transmission and acceptance of new behaviors but they may also affect genetic inheritance.

We argue that the function of human culture is to clarify what people value. Consequently, nothing in cetacean behavior (or any other animal's behavior) comes remotely close to this aspect of human culture. This does not mean that the traditions observed in cetaceans are uninteresting, but rather, that we need to understand why they are so different from our own.

Social learning and imitation is central to culture in cetaceans. The training technology used with cetaceans facilitates reinforcing imitation of one dolphin's behavior by another; the same technology, now widely used by pet owners, can lead to imitative learning in such unlikely species as dogs and horses. A capacity for imitation, and thus for cultural learning, may exist in many species.

Assessments of cetacean behavior has been hampered by popular misconceptions and mythic imagery. Rendell and Whitehead argue persuasively for accepting the idea of cetacean culture. Approaches to “culture,” however, must resist positivist approaches that reaffirm the observable. Culture is also comprised of “lacunae” when organisms choose to resist or avoid behavioral patterns.

Sociality may not be a defining feature of social learning. Complex social systems have been predicted to favour the evolution of social learning, but the evidence for this relationship is weak. In birds, only one study supports the hypothesis that social learning is an adaptive specialisation to social living. In nonhuman primates, social group size and social learning frequency are not correlated. Though cetaceans may prove an exception, they provide a useful group with which to test these ideas.

Rendell & Whitehead's minimalist definition of culture does not allow for the important gaps between cetaceans and humans. A more complete analysis reveals important discontinuities that may be more instructive for comparative purposes than the continuities emphasized by the authors.

While cetaceans clearly show social learning in a wide variety of contexts, to label this as “culture” hides more than it reveals: we need a taxonomy of culture to tease apart the differences rather than hiding them in a catch-all category.

Rendell and Whitehead state that marine ecosystems are more variable than terrestrial ecosystems over time scales of months or longer. The marine environment is actually less variable than the terrestrial at these shorter time scales, and probably equally variable over centuries. This issue is important when considering claims that environmental variability affects benefits of social learning versus individual learning and genetics.

While supporting the claim for culture in cetaceans, I suggest that Rendell and Whitehead's argument is potentially incomplete if based solely on ethnographic evidence. The notion of cetacean culture can also be explored experimentally. I hope to complement the authors' assertion by discussing dolphin brain and behavioural research findings, thus contributing to a more holistic argument for culture in dolphins.

Rendell and Whitehead adopt a weak definition of culture to allow low standards of evidence for marine mammals, but they do not adequately rule out genetic factors or individual versus social learning. They then use these low standards to argue that some whales have unique cultures only matched by humans. It would have been more helpful to specify data gaps and suggest critical tests.

Recent evidence suggests imitation is more developed in some cetaceans than the authors imply. Apart from apes, only dolphins have so far shown a grasp of what it is to imitate; moreover dolphins ape humans more clearly than do apes. Why have such abilities not been associated with the kind of progressive cultural complexity characteristic of humans?