Dolphins: Second-Smartest Animals?

New MRI analysis shows dolphins are smarter and more self aware than scientists had realized.


- New research suggests that dolphins are second only to humans in smarts.

- MRI scans indicate that these marine mammals are self-aware.

- Researchers think dolphins are especially vulnerable to suffering and trauma.

When human measures for intelligence are applied to other species, dolphins come in just behind humans in brainpower, according to new research. Dolphins demonstrate skills and awareness previously thought to be present only in humans.

New MRI scans show that dolphin brains are four to five times larger for their body size when compared to another animal of similar size, according to Lori Marino, a senior lecturer in neuroscience and behavioral biology at Emory University, and one of the world's leading dolphin experts. Humans also possess an impressive brain-to-body ratio.

"If we use relative brain size as a metric of 'intelligence' then one would have to conclude that dolphins are second in intelligence to modern humans," said Marino, who performed several MRI scans on dolphin brains.

Marino will be presenting her findings at next month's American Association for the Advancement of Science meeting.

"Size isn't everything," she admitted, but she says at least two other lines of evidence support her claims about dolphin intelligence.

First, various features of the dolphin neocortex -- the part of the brain involved in higher-order thinking and processing of emotional information -- are "particularly expanded" in dolphins.

Second, behavioral studies conducted by Marino and other experts demonstrate that dolphins exhibit human-like skills. These include mirror self-recognition, cultural learning, comprehension of symbol-based communication systems, and an understanding of abstract concepts.

Marino believes these findings suggest that marine park shows, "dolphin-assisted therapy" facilities and other forms of captivity "are potentially psychologically harmful to dolphins and present a misinformed picture of their natural intellectual capacities."

"This point is based on the simple proposition that the more aware an individual is of one's present and future circumstances, the more intensely one may feel the difference between a pleasant and unpleasant situation, or the more one can think about, and thus experience, negative feelings and ruminate about the negative consequences of one's circumstances," said Marino.

"If this proposition is not true," she added, "then there is no basis for assuming humans suffer more than any other given animal."

She pointed out that during dolphin drives, when the animals are herded together by boats, some dolphins become so panicked that they die of heart attacks. Others die from exhaustion attempting to flee, while still others become entangled in nets and are killed or injured.

The dolphins that do survive are hoisted from the water, often by their tail flukes, and transported to the human-run parks and other facilities.

"The scientific evidence on dolphin sensitivities reveals that they are vulnerable to trauma and suffering when forced to live in the confined context of marine parks," Marino said.

Gay Bradshaw, director of The Kerulos Center, which provides sanctuary and support for animals suffering from human-caused trauma, agrees with Marino's determinations, saying, "What Dr. Marino states is congruent with theory and data."

At the AAAS meeting, Diana Reiss, a professor of psychology at Hunter College, plans to present findings from additional behavioral studies that support Marino's conclusions about dolphins.

New MRI scans of dolphin brains shows that the animals are second only to humans in intelligence.


Originally designed to live on land, marine mammals are a diverse, charismatic group of animals that include more than 120 species. The animals share key characteristics of land mammals. They have hair, breathe air, give birth to live young, which feed off mother's milk when young. They have warm bodies and usually thick blubber to keep their body temperatures high. The bottlenose dolphin is probably the most widely recognized marine mammal, easily spotted just offshore from beaches around the world. Small groups of 20 or less can live in close proximity to shorelines, but groups living more offshore can reach several hundred. Bottlenose dolphin calves stay with their mothers for up to six years, learning how to hunt and become good dolphin citizens. Full-grown dolphins reach eight to 12 feet in length and can weigh up to 1,430 pounds. The bottlenose dolphin is protected in U.S. waters.

Humpback Whale

What makes them "marine" depends on the animal. They either live mostly in the sea or, like polar bears, depend on the ocean for food. The largest in the group are whales -- including humpback whales. These massive animals reach up to 50 feet in length and weigh up to 79,000 pounds. To maintain their weight, the animals feed on tons of krill and fish. They neared extinction due to whaling, but have recovered somewhat since a 1966 moratorium on whaling was introduced.

Polar Bear

While polar bears live mostly on land or ice, they are excellent swimmers and have been known to swim up to 45 miles a day. The massive animals, weighing up to 1,500 pounds, hunt mostly seals. In recent years, biologists have observed that the bears are swimming now more than ever as melting stretches the distances between Arctic ice flows. Because they depend on sea ice to hunt seals, the polar bear is considered threatened as global warming melts and thins ice in this region.

Sea Otter

This member of the weasel family is also the smallest marine mammal, with females weighing about 60 pounds and males weighing up to 90 pounds. They may be small, but they're also clever. They're the only marine mammals known to use tools. They use stones to break open clams and store food they gather in the folds of their armpits! Another feature that sets them apart is their lack of blubber. These marine mammals depend mostly on their fur to stay warm. That feature makes them particularly vulnerable to oil spills, which can compromise their fur's insulating effect.

Sea Walrus

Immediately recognizable by its long tusks and whiskers, the sea walrus is a hefty, flippered member of the Odobenidae family and is, in fact, the last living member of this group. Since both the males and females have big tusks and not much for teeth, the animals feed by sucking up shellfish from the ocean floor. So, just what are those tusks for? The longer they are (they grow to be up to four feet long in males), the higher an animal is ranked in the group. Males attack each other with their tusks to establish dominance. The ivory appendages are also handy for poking holes in the winter ice and for helping the animals pull themselves out of the water.


Manatees, also known as sea cows, are gentle herbivores that live in marshy areas in tropical and subtropical waters. The average adult manatee can weigh up 1,200 pounds and is around 10 feet long. Because of their slow metabolism, these animals can only survive in warm waters. Due to the unusually long, cold winter this year in part of the southeastern United States, populations of manatees throughout Florida were devastated. During the day, manatees usually like to stay close to the surface. At night, manatees will often sleep about three to 10 feet below sea level. This is why these gentle animals are so often accidentally injured, maimed or killed by passing boats.

Harbor Seal

Found up and down the North American coastlines, these marine mammals spend half of their lives swimming. Although they can reach up to six feet in length and weigh around 180 pounds, when on land and in plain sight harbor seals may not be easy to spot. Their spotted brown or tan fur allows harbor seals to blend in with sand and rocks. Unlike their very vocal relatives -- sea lions and elephant seals -- harbor seals are quiet creatures that make little noise. They like to hang out on beaches, sand bars and rocks during low tide to bask in the sun and sleep, but they never go far from the water. At the slightest sign of danger, they will quickly slip back under the waves. These expert swimmers have been known to plunge to depths of more than 1,600 feet and stay underwater up to 28 minutes.