Emory scientist finds different paths lead to similar cognitive abilities

Despite the divergent evolutionary paths of dolphins and primates — and their vastly different brains — both have developed similar high-level cognitive abilities, says Emory University neuroscientist and behavioral biologist Lori Marino. She presented her latest findings on the evolution of and differences in brain structure between cetaceans (ocean mammals like whales and dolphins) and primates April 5 during the 14th annual Experimental Biology 2005 meeting in San Diego.

Marino’s presentation examined the diverse evolutionary patterns through which dolphins and primates acquired their large brains, how those brains differ, and how sensory information can be processed in different ways and still result in the same cognitive abilities.

“Eventually, a better understanding of how other species process information might be useful in helping people impaired in “human” ways of processing information. Perhaps there are alternative ways to sort out information in our own brains,” says Marino, whose talk was part of the scientific sessions of the American Association of Anatomists.

Recent research by Marino and her colleagues has traced the changing encephalization, or relative brain size, of cetaceans during the past 47 million years by using magnetic resonance imaging and histological studies of the fossil record. While modern humans have brains that are seven times bigger than would be expected for our body size, giving us an encephalization level of seven, some modern dolphins and whales have an encephalization level close to five — not a huge difference, says Marino. For example, Homo sapiens’ closest relatives, the great apes, have encephalization levels of only two to two-and-a-half.

“While humans are the most encephalized — the brainiest — creatures on earth, we are relative newcomers to that status,” says Marino. “The cetaceans enjoyed a tremendous increase in brain size and organization about 35 million years ago, whereas humans got their big brains much more recently during the past one to two million years.”

Marino’s earlier research has shown how dolphins have the capacity for mirror self-recognition, a feat of intelligence previously thought to be reserved only for Homo sapiens and their closest primate cousins. Marino is a professor of neuroscience and behavioral biology at Emory and a research associate at the Yerkes National Primate Research Center. Her work has been funded by the National Science Foundation, The SETI Institute, The Smithsonian Institution, and Emory University.