Evolution of Whales and Dolphins: From Land to Sea

Introduction to Cetacean Classification

Dolphins, porpoises, and whales belong to one of two cetacean families: the Platanistidae (freshwater dolphins) or the Delphinidae (which includes all other dolphins, porpoises, and the cetaceans commonly called whales). The distinction between porpoises and dolphins has caused considerable confusion, as the names are sometimes used interchangeably. There is, however, a technical difference: true porpoises are limited to a few species within the family Delphinidae that possess spade-shaped teeth; all the rest are properly called dolphins (Green, 1990).

How did whales and dolphins evolve? In his essay "The Social Function of Intellect," Nicholas Humphrey (1976) observed: "The open sea is an environment where technical knowledge can bring little benefit and thus complex societies — and high intelligence — are contraindicated (dolphins and whales provide, maybe, a remarkable and unexplained exception)." This observation helped launch the "Machiavellian intelligence" hypothesis, which proposes that more intelligent animals evolved into social, grouping, and cooperating creatures. The hypothesis is now widely accepted, though it has received relatively little attention in discussions of whale evolution, except among a few cetologists.

Science continues to add to our knowledge of animal social systems and behavior. Of the mammals known collectively as dolphins and whales — which belong to the same order — only about eighty-five species remain. Of these, only four have received the great majority of scholarly attention regarding their evolution: the killer whale (Orcinus orca), the bottlenose dolphin (Tursiops spp.), the humpback whale (Megaptera novaeangliae), and the sperm whale (Physeter macrocephalus). Because the sperm whale possesses the largest brain on earth, has great commercial significance, and maintains a highly social lifestyle, it has received the most intensive study.

Cetacean Intelligence, Social Behavior, and Culture

Studies of animal culture have not historically included whales. However, several field studies have now been undertaken. Observing patterns of behavioral variation in wild populations that cannot be explained by either genetic or environmental factors reveals good evidence for culture in several cetacean species. The bottlenose dolphin (Tursiops) shows the strongest evidence of sophisticated social learning abilities, including vocal and motor imitation, though many other species have yet to be studied in comparable depth. Researchers have also observed imitation and teaching behaviors in killer whales.

Experimental data alone cannot provide the full picture of culture in whales. The complex and stable vocal and behavioral traditions found in groups of killer whales (Orcinus orca) appear to have no parallel except among humans. These animals form an independent group that has evolved cultural faculties. Key factors in their study include the worldwide movements of cetaceans, the great variety of marine environments, large temporal scales relative to those on land, and stable matrilineal social groups. As Rendell and Whitehead (2001) noted, "There have been suggestions of gene-culture coevolution in cetaceans, and culture may be implicated in some unusual behavioural and life-history traits of whales and dolphins."

Sperm whales' interactions with one another are relatively accessible for observation and study. Their daily routines — including birth, predation, and death — have been examined extensively. Some of their behaviors are unusual and unexpected when compared to the sociological and ecological routines of land-dwelling animals. Many elements of sperm whale biology are directly tied to their ecology and behavior.

References

Chadwick, Douglas. Whales, Dolphins and Porpoises, 2nd ed. Checkmark Books / National Geographic, 1999.

Chadwick, Douglas. "Evolution of Whales." National Geographic, November 1, 2001.

Green, John. Whales and Dolphins Coloring Book. Courier Dover Publications, 1990.

Hasegawa, M., Adachi, J., & Milinkovitch, M.C. "Novel Phylogeny of Whales Supported by Total Molecular Evidence." Journal of Molecular Evolution, 44 (Suppl. 1): S117–S120, 1997.

Humphrey, Nicholas. "The Social Function of Intellect." In Bateson, P.P.G. and Hinde, R.A. (Eds.), Growing Points in Ethology, Chapter 9, pp. 303–317. Cambridge University Press, 1976.

Milinkovitch, M.C., & Thewissen, J.G.M. "Even-toed Fingerprints on Whale Ancestry." Nature, 388: 622–624, 1997.

Ogawa, R., and Kamiya, T.A. "Case of the Cachalot [Sperm Whale] With Protruded Rudimentary Hind Limbs." Scientific Reports of the Whales Research Institute, No. 12, pp. 197–208, 1957.

Rendell, Luke, and Whitehead, Hal. Behavioral and Brain Sciences, 24: 309–324. Cambridge University Press, 2001.

Struthers, John. "On the Bones, Articulations, and Muscles of the Rudimentary Hind-Limb of the Greenland Right-Whale (Balaena mysticetus)." Journal of Anatomy and Physiology (London), Vol. 15, pp. 141–321, 1881.

Thewissen, Hans. "Digital Library of Dolphin Development." The Thewissen Lab, November 4, 2006.