Clearly, for a mechanism of phenotypic variation to contribute to evolution it must be hereditary; that is why so much of evolutionary biology concerns genetic science and molecular biology. However, not all heredity is genetic, there is an alternative form of heritable variation which can be seen in a species that is reputed to be the most widely distributed mammal in the world, after humans1.
Killer whales (Orcinus orca) are highly social animals: they live in familial groups, have complex patterns of vocal communication, and coordinate some of their activities including cooperative hunting. There are several types of killer whales, differing in their morphology (body markings, appendage shape and size), in the marine areas and habitats they prefer, and the animals they prey upon (fish, marine mammals and birds). Importantly, these animals have culture: complex behaviour that is specific to individual social groups and passed on between and within generations through social learning. Socially maintained behaviour includes food preference, for example rigidly exclusive diets of either fish or marine mammals that are distinctive characteristics of some killer whale types, together with the techniques used to hunt them. The complex sounds used for hunting, navigation and communication, are also distinctive for different groups (including dialects specific to individual killer whale pods and clans) and are probably socially learned1 2.
Image credit:
Viki Kolatkova
https://uk.inaturalist.org/photos/92291143
Killer whale behaviour (e.g. different hunting methods associated with individual groups’ preferred prey) probably reflects their intelligence. Intelligent social animals such as apes and dolphins (killer whales are part of the oceanic dolphin family) are known to experiment and develop complex behaviours such as tool-use3. Killer whales, then, are likely to develop new behaviour through innovation2. This ability to develop successful new behaviour and for it to spread and be maintained in animal groups by cultural learning is a strongly adaptive capability, enabling animals to improve their activities and react behaviourally to environmental changes, be they threats or opportunities. Maintenance of behaviour through successive generations through cultural learning is a non-genetic form of heredity.
”Maintenance of behaviour through successive generations through cultural learning is a non-genetic form of heredity”
”Gene-culture interactions mean that culture in animals is an evolutionary mechanism”
Another important aspect of culturally maintained behaviour is that, being adaptive, it affects fitness. Consequently, Killer Whale familial groups that have successful variations in behaviour can have selective advantage over other groups. The resulting increased success of the former group might therefore lead to it expanding and increasing as a proportion of a wider orca population, a case of natural selection acting on a non-genetic, behavioural variation. Should that occur, other phenotypic variations in the behaviourally favoured familial group (which, for example, might be morphological such as differences in body markings or appendage shape, or biochemical such as altered digestive enzymes) will follow selection of the behavioural variation; their presence in the wider population will increase as the group expands. Such phenotypic variations will, of course, be genetically encoded, which means that a culturally inherited adaptation also causes, indirectly, a genetically based change in a population. Gene-culture interactions of this kind mean that culture in animals is an evolutionary mechanism2 4.
The evolutionary power of this non-genetic mechanism is illustrated by strong evidence suggesting that behaviourally based gene-culture interactions of this kind may have generated the divergence of killer whales into several different types. Historically considered to be variants of the single species Orcinus orca, these “ecotypes” are so distinct that they may be approaching division into separate new species2.
Image credit: Damien Sanders ©
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References
- Ford, John K.B. ‘Killer Whale’. In Encyclopedia of Marine Mammals, 650–57. Elsevier, 2009. https://doi.org/10.1016/B978-0-12-373553-9.00150-4 [↩] [↩]
- RIESCH, RÜDIGER, LANCE G. BARRETT-LENNARD, GRAEME M. ELLIS, JOHN K. B. FORD, and VOLKER B. DEECKE. ‘Cultural Traditions and the Evolution of Reproductive Isolation: Ecological Speciation in Killer Whales?’ Biological Journal of the Linnean Society 106, no. 1 (1 May 2012): 1–17. https://doi.org/10.1111/j.1095-8312.2012.01872.x [↩] [↩] [↩] [↩]
- ‘Tool Use by Animals’. In Wikipedia, 23 May 2022. https://en.wikipedia.org/w/index.php?title=Tool_use_by_animals&oldid=1089333875 [↩]
- Whitehead, Hal, and John K. B. Ford. ‘Consequences of Culturally-Driven Ecological Specialization: Killer Whales and Beyond’. Journal of Theoretical Biology 456 (07 2018): 279–94. https://doi.org/10.1016/j.jtbi.2018.08.015 [↩]