Marino: Dolphins check their look in the mirror, too

By Michael Terrazas mterraz@emory.edu

It’s long been suspected that dolphins are the smartest creatures in the sea. But a recent study by Lori Marino suggests the marine mammals are even more intelligent than previously known and possess cognitive abilities thought to exist only in humans and great apes.

Marino, a lecturer in neuroscience and behavioral biology, conducted a three-year study with Diana Reiss, a senior research scientist at the New York Aquarium in Brooklyn, that shows dolphins have the capacity for mirror self-recognition (MSR), a feat of intelligence heretofore thought to be reserved only for Homo sapiens and their closest cousins. The findings were published this past spring in the Proceedings of the National Academy of Sciences.

Marino and Reiss used what is known as a “mark test” to measure the trait; with bottlenose dolphins as their subjects, the researchers marked the animals with a dye in a location not normally visible (for example, the side of the dolphin’s head). In every case, as soon as the animal was marked, it raced to an underwater mirror to check out its look.

The finding holds implications not just for marine biologists or dolphin enthusiasts, but for people like Marino who study cognitive processes and neuroanatomy. Dolphin brains lack a frontal lobe, the region of the brain thought to be responsible for many higher cognitive functions in primates. This finding suggests that, while the frontal lobe certainly plays a major role in primate intelligence, it is not the basis for intelligence in dolphins.

“This is really a striking case of convergent evolution,” said Marino, using a term that means the same trait evolving independently in different species. “It’s interesting that two very different lineages of mammal show the same, very rare capacity. The brains of primates and of dolphins are so different—they haven’t shared a common ancestor for at least 90 million years.”

It also means Marino’s conclusion is finding some resistance among scientists who have a stake in certain theories of cognition that would require revision if dolphin MSR is true. But Marino, a research associate in the Living Links Center at Yerkes, brushed off such professional cynicism with the hope that other researchers replicate her findings.

“Most of my colleagues, especially those who have worked with dolphins, are not surprised by the finding because they’ve had experience with the intelligence of this animal,” Marino said. “Dolphins, chimpanzees and great apes show the same sort of affinity for [certain cognitive] tasks, so I think the proof is in the pudding.”

She also said that working with colleagues like Frans de Waal, one of the world’s leading primatologists, has helped her immensely. “My association with Living Links has been invaluable,” she said. “Frans is a broad-minded scientist and has some very interesting ideas about what the distribution of higher-level cognitive capacities might be in the animal kingdom.”

Marino has been working with dolphins since graduate school, and though she said it can be inconvenient working with an animal not readily available—the closest live dolphins (not swimming free in the ocean) are likely those at Sea World in Orlando, Fla.—she has not had many problems finding research subjects.

“Most of my research on dolphins is on their brain, and I get those postmortem from stranded animals,” Marino said. “But I’ve been able to get access to [live dolphins] and conduct tests. Things are more possible than you would imagine—if you’re persistent.”