The big brains of whales and dolphins – the largest on the planet – evolved to keep themselves warm in cold oceanic waters, according to research published March 9 in the journal Scientific Reports.
“What is really cool about this study is that we show that cetaceans have specialized internal metabolic machinery to heat their brains, using similar processes that hibernating animals, such as bears, employ to heat their bodies during the winter,” says Muhammad Spocter, Ph.D., associate professor of anatomy at DMU and one of the authors of the research. “This is quite a remarkable finding and one that has implications for our understanding of brain evolution.”
Whales’ and dolphins’ large brains, some weighing more than 17 pounds, have often been cited as evidence of high intelligence in cetaceans. This recent research, however, highlights scientific evidence from a long-term study led by Paul Manger, Ph.D., that these mammals’ brains lack the diversity, flexibility and adaptability in their mental processes and behavior that humans have. Instead, their brains evolved to keep the neurons within the brain warm in cold waters.
That’s important, because even a small drop in brain temperature makes many neurons inactive, greatly reducing mental activity. Whale and dolphin brains became exceptionally large around 32 million years ago, 20 million years after they became fully aquatic and around the time when there was a major drop in oceanic water temperatures across the planet.
“What we have found is that majority of the cells, neurons and glia, forming the brains of whales and dolphins have the internal chemistry required to function as the brain’s own heating elements,” says Dr. Manger, lead author and a research professor in the School of Anatomical Sciences at the University of the Witwatersrand in Johannesburg, South Africa. He first proposed in 2006 that the large size of brains in whales and dolphins is an adaptive evolutionary response to the challenges of living in a cold aquatic environment. “These ‘heating elements’ are less numerous in the brains of land-living mammals, such as the closely related hippopotamuses, pigs, buffaloes, camels and antelopes.”
Authors of the paper, titled “Amplification of potential thermogenic mechanisms in cetacean brains compared to artiodactyl brains,” represent several countries: South Africa, the United States, Iceland, Denmark, Saudi Arabia, Sweden and Japan.
“It’s a good example of how an international team of researchers can get together and draw on their expertise to answer a single question,” says Dr. Spocter, who, as the lead quantitative morphologist on the study, designed and implemented the cell counting and quantification approach on tissue slides and put together the statistical comparisons.
While the concept that whales and dolphins do not appear to be more intelligent than the average mammal might disappoint some, the researchers say understanding these creatures for what they really are, rather than what we may wish them to be, is crucial for protecting them.
“Knowing how central water temperature is to their survival may allow us to understand what will happen to certain species of whale and dolphin during the inevitable rise in oceanic temperatures associated with human-induced climate change,” Dr. Manger says. “It is quite possible that some species may die through overheating, becoming victims of global warming. This understanding may allow us to direct our efforts in the most appropriate way to secure the future of as many whale and dolphin species as possible.”
Adds Dr. Spocter: “These findings highlight the point that organisms with large brains – e.g., dolphins, humans and elephants – did not necessarily evolve large brains for the same reasons – i.e., increased intelligence. If we forget this, one might ignore important differences in brain morphology which are unique to each group and which help us explain differences in behavior and brain function.”