N o one has ever been able to fully measure the intelligence of whales, dolphins, and porpoises, but evidence continues to mount that it is impressive. Consider Kelly, a dolphin formerly housed at the Institute for Marine Mammal Studies in Mississippi. She was trained to keep her outdoor tank clean. If she brought a piece of litter to her trainer, she was awarded with a fish.
The enterprising Kelly figured out that if she wedged a single piece of litter under a stone and ripped it into multiple pieces, she would receive more fish. She then determined that she could increase the amount of “litter” in the tank by using the earned fish as bait to catch unwary birds. She subsequently taught these clever strategies to her calf.
Dolphins like Kelly, along with whales and porpoises, all engage in sophisticated behaviors that tend to be mostly associated with humans. They live in tightly knit social groups, have complex relationships, communicate with each other using language-like vocalizations, and even have regional dialects.
New research links this complexity of cetacean culture and behavior to the size of their brains. The findings, published in the journal Nature Ecology & Evolution, position these marine mammals with humans and other primates in an elite and very brainy group.
“Each species’ brain is unique, but primates and cetaceans do share some features that are rarely found elsewhere in nature,” lead author Kieran Fox of Stanford University’s department of neurology and neurological sciences told Seeker. “One is the sheer size of their brains in absolute terms. They are the biggest in the world, and in the case of the whales, the largest brains ever to appear on the planet.”
“Additionally,” he continued, “primates and cetaceans both tend to have large brains relative to the size of their bodies.”
Co-author Michael Muthukrishna, a researcher at Harvard University and the London School of Economics and Political Science, explained that, in general, larger brains are able to store and manage more information than smaller brains. Braininess comes with a price, though, as such tissue is incredibly energetically expensive.
“The larger your brain, the more calories you need to support it, so actually you’re better off with the smallest brain you can get away with,” Muthukrishna said. “Bees are a nice example. They can do quite a lot with their small brains.”
Researchers have wondered why encephalization — brain expansion — evolved in some animals but not others. A related question is: Why do large brains, complex societies and large socially learned behavioral repertoires co-occur?
To investigate the matter, Fox, Muthukrishna, and senior author Susanne Shultz of the University of Manchester assembled the world’s largest dataset of information on brain size, social structures, and cultural behaviors across cetacean species.
Efforts by biologists to gather such data over the decades have been rough, since the work often involves following groups of marine mammals in the wild over long periods and then documenting observed behaviors.
Fox served as an intern studying humpback and fin whales as part of the Mingan Island Cetacean Study, which contributed to the enormous dataset.
“I can attest that it’s cold, wet, and uncomfortable work a lot of the time!” Fox said.
For the new study, Fox and his team first disentangled the relationships between brain size, body size, social behavior, and ecology. One could argue that cetaceans and primates just have large brains to match their large bodies. The researchers also wanted to control for the evolutionary relatedness of the species they studied.
“It’s like having a family who were red-headed and tall and assuming being red-headed was related to being tall, when, instead, both may have been present in their grandparents just by chance, such that the two traits don’t really have any meaningful relationship,” Muthukrishna explained.
The researchers found that cetacean encephalization is predicted by both the species’ social structure and group size. Moreover, they found that evolved brain expansion in the marine mammals predicts the breadth of social and cultural behaviors, as well as ecological factors, such as the diversity of their prey types and latitudinal range.
The findings provide evidence for two related theories: the Social Brain Hypothesis and the Cultural Brain Hypothesis. Each theory makes predictions about the various relationships between brain size, features of societal organization, lifespan, length of childhood, and social learning, among other factors.
Previously, primates were used to test out these theories, but because humans are primates, the studies could only go so far.
“For example, ours and chimp ancestors may have lived in close groups and had fairly large brains for unrelated reasons,” Muthukrishna said. “We wanted to test these hypotheses with cetaceans because they are so alien to us. They’re evolutionarily distant, and their underwater world may as well be a different planet compared to the land we inhabit.”
The study suggests that large brains tend to co-evolve with sociality, behaviors learned socially from other members of the group, and longer childhoods. There is then a feedback loop, where these behaviors tend to promote encephalization.
As for what started the increased brain growth in the first place, the researchers speculate that calorie-rich edibles must have been available, and the environments must have been fairly stable in order to support social learning.
Fox also noted that primates and cetaceans each have a cortex that is “massively enlarged.” The cortex, he explained, is the outermost part of the brain that is wrapped around the older evolved structures sort of like the bark of a tree. It is the brain area that is typically attributed to higher cognitive functions like reasoning and language.