Like many people, I find dolphins fascinating. It’s not that I think they’re “better” or “more than” other animals. But I have devoted a fair amount of time to thinking about them (during my graduate work and otherwise). Because I do talk about them so much, I thought it would be nice to take a few minutes to talk more generally about dolphins. This is basic stuff, and by no means exhaustive (even if I could tell you all that the brightest human minds currently know about dolphins, my guess is that we’d still have a great deal to learn), but we might refer back to some of it in future conversations about our relationships with dolphins…
Dolphins are aquatic mammals, classified as belonging to the order called Cetacea, which is made up of whales, dolphins, and porpoises. Cetaceans are divided into odontocetes (toothed whales) and mysticetes (untoothed whales, mostly the great whales who use baleen to strain the water for tiny organisms to eat). Dolphins, orcas, porpoises, freshwater river dolphins, and sperm whales are all considered odontocetes, which is why dolphins are essentially thought of as small toothed whales. Evidence suggests that modern cetaceans originated from a land mammal that is thought to have returned to the sea some 50 to 60 million years ago. Many people are familiar with bottlenose dolphins (Tursiops truncatus), those most often on display at marine parks and aquariums and the species of dolphin that starred in the Flipper shows and movies. Still, there are more than 30 different species of dolphins worldwide. Like humans, dolphins are highly social and most live in groups ranging from a few members to thousands. They generally devote substantial time and energy to caring for their young and engaging in relationships, some of which have been documented to span decades.
Dolphins have a complex brain. The brain’s cortex is where information is received, organized, analyzed, and stored in mammals, and the surface area of the dolphin cortex is enormous in relation to the rest of the brain (and compared to human brains-the former averaging 3,700 centimeters squared, and the later 2,300 centimeters squared).Dolphin brains are also asymmetrical; asymmetry in humans is associated with such sophisticated mental abilities as language.The dolphin brain is actually similar to the human brain in complexity and convolutions, in brain to body weight ratio, and in neural complexity. (Dolphin brains differ from humans’ in the overall structure and organization, connections to the limbic system and probably other ways that are not yet identified). Dolphin brains are thought to have evolved in a similar process as those of humans, related to the needs and pressures for complex communication and elaborate societies–but dolphin brains, as they are now, have been around millions of years longer than the modern human brain. In fact, humans have had the brain we do for about 100,000 years; dolphins have had the same sized brains (or larger) than ours for about 15 million years.
Dolphins rank higher in encephalization quotient (EQ), the ratio of the brain volume to the surface area of the body, than great apes and have been placed only second to humans. The EQ is significant because it gets higher as the subjects’ social structures get more complex. But some suggest that the EQ measurement may be underestimated in dolphins because of the additional weight of blubber in the cetacean body (see Marino, further resources below). This indicates that dolphins, therefore, may have at least the marine parallel to the human EQ.
With relatively large brains and a substantial cerebral cortex, it is widely accepted in the scientific community that dolphins have considerable cognitive abilities. They communicate with one another using a complex system of whistles, body language, and touching that is not fully understood by dolphin scientists. Dolphins also have learned to communicate with us, if only partially, through the use of a human-created artificial language. In addition, scientists and dolphin trainers agree that dolphins have a rich emotional life, including a sense of humor, and people who regularly work with them often speak of dolphins as having distinct personalities.
Dolphins also exhibit a sense of self. Rigorous studies indicate that dolphins recognize their own reflections in a mirror-a very rare capability in the animal kingdom that was only confirmed in humans and great apes before a recent study showed that dolphins also share this capacity.In experiments with captive dolphins at the New York aquarium, researchers first marked the dolphins with “sham” marks, and then exposed them to a mirror. After several repetitions, the scientists put temporary black ink on parts of the dolphins’ bodies, which they could see only in a mirror. In each of the trials, the dolphins went to the mirror to examine the areas the scientists had marked.
Until very recently, scientists believed that self-recognition was possible only in animals with a frontal lobe, such as humans and other primates. Recent dolphin self-recognition studies, however, suggest that mirror recognition is probably linked with more general characteristics, such as large brain size and cognitive ability (especially because dolphins’ and primates’ brains evolved along very different lines). In any event, the research indicates that dolphins have an acute sense of themselves and others.
Self-awareness is also indicated by dolphins’ use of signature whistles–the equivalent of a unique name–which they apparently use to call one another when separated over distance, among other things.In addition, scientists have found that dolphins, like humans, act independently of instinct, biological drive or conditioning. Indicating what would be called “free will” in humans, dolphins make purposeful choices and conscious decisions in their lives, even when it comes to sexual activity and eating.
Dolphins also show that they understand responsibility, both as relates to other dolphins and other species. Moreover, dolphins often demonstrate altruistic behavior, such as routinely baby-sitting for one another, and assisting dolphins who are hurt or distressed for no apparent gain to themselves.
All in all, dolphins apparently share a suite of attributes with humans-many of which humans believed until recently that we alone possessed, such as intelligence, emotions, and self awareness. But dolphins also have inner and outer worlds that are completely foreign to us. They are marvelously suited for their watery environment with muscled, streamlined bodies, a powerful tail fluke to propel them through the water, and pectoral fins with which to steer. Their blowhole allows dolphins to breathe efficiently with only a small amount of their bodies out of the water and their lungs are made up of twice the capillaries of human lungs, which, along with other anatomical attributes, allows dolphins to dive deeper, surface more quickly and remain under water far longer than any human is capable of doing without aid. Most remarkably, dolphins navigate their world primarily through the use of senses we do not have. For dolphins, sound is the primary perception tool, but their use of sound is far more complex than a human’s. Using a sophisticated system of echolocation, dolphins project sonic clicks that return echoes that portray a three-dimensional image of the world around them. As sound passes through living tissues, dolphins routinely “see through” each other and every other living organism.
Perhaps what amazes me most is the combination of their familiarity on the one hand, and their exotic other-worldliness on the other.Knowing what we do about dolphins–and understanding that there is so much we do not fully understand about them-how does that figure in the ways we think about them? More than that, ought knowing these creatures as socially complex, feeling, sapient individuals have a considerable impact on how we interact with them?
Further Resources:
Griffin, D. (2001). Animal minds: Beyond cognition to consciousness. Chicago: University of Chicago Press.
Herzing, D. L., & White, T. I. (1999). Dolphins and the question of personhood. Etica & Animali.
Marino, L., Rilling, J. K., Lin, S. K., & Ridgway, S. H. (2000). Relative volume of the cerebellum in dolphins and comparison with anthropoid apes. Brain, Behavior and Evolution, 56, 204-211.
Pryor, K., & Norris, K. S. (Eds.). (1991). Dolphin societies: Discoveries and puzzles. Berkeley: University of California Press.
Reiss, D., & Marino, L. (2001). Mirror self-recognition in the bottlenose dolphin: A case of cognitive convergence. Proceedings of the National Academy of Sciences, 98(10), 5937-5942.
Reynolds, J. E. I., Wells, R. S., & Eide, S. D. (2000). The bottlenose dolphin: Biology and conservation. Gainesville: University Press of Florida.