For decades, it's been common knowledge that dolphins are among the world's smartest species. Now some researchers -- and a new book -- argue the supposed underwater geniuses aren't so special after all.
Their social lives are complex, and they can congregate in large groups. Their heart rates increase when they notice a family member suffering. They sound the alarm when they discover food or a potential threat. And experiments have shown they even anticipate future events.
Biologist Justin Gregg is talking about chickens.
Chickens, says Gregg, "are not as dim-witted as popular opinion would have us believe." He adds, "Some of these complex behaviours have also been observed in dolphins."
Really? Are chickens as smart as dolphins? Or, to put it differently: "Are dolphins really smart?" This is the question Gregg, a zoologist with the U.S.-based Dolphin Communication Project, asks in his new book of the same name. And he isn't the only one finding fault with Flipper's brainpower.
For more than 50 years, the dolphin has been viewed as an especially intelligent creature, grouped together with human beings and great apes. But now a dispute on the subject has erupted among scientists, and the smart aleck of the seas may end up being just an average mammal. "We put them on a pedestal for no reason and projected a lot of our desires and wishes on them," says neuroethologist Paul Manger of the University of the Witwatersrand in South Africa. According to the professor, the claims that dolphins have a particularly complex brain, use a sophisticated language, are self-aware and can use tools are nonsense.
In some cases, says Manger, dolphins -- which are small whales -- are even outdone by goldfish. When goldfish are placed in a bowl, he explains, they at least try to escape by boldly jumping out, whereas dolphins that have been captured in nets won't even think of jumping to freedom. "The idea of the exceptionally intelligent dolphin is a myth," Manger concludes.
One measure scientists use to determine a creature's intelligence is brain size -- given the theory that the more a brain weighs relative to the body, the smarter the animal. A human brain, which weighs about 1,300 grams (46 oz.), makes up about two per cent of body weight. A chimpanzee's brain comprises 0.9 per cent of its weight, while the corresponding number in elephants, with their brains weighing in at more than 4.5 kilograms (9.9 lbs.), is 0.2 per cent. Dolphins do well by comparison. The brain of a bottle-nosed dolphin, for example, weighs more than 1,800 grams, or 0.9 per cent of its average body weight.
It seems logical that dolphins deserve to be included in the animal Mensa Society. But does a large brain mean the same in marine mammals as it does in terrestrial animals? In 2006, Manger noted that whales developed a large brain in order to keep the organ from becoming hypothermic, and thereby useless, in cold water.
Manger described an unusually high density of so-called glial cells in the animals' brain matter. He explained that these cells act like tiny ovens to keep the brain warm. Besides, he added, dolphins have a relatively simple brain structure, and noted: "The essential features of complex neural processing of information, as observed in other mammals, are missing or poorly developed."
Manger has now upped the ante with a new paper in which he claims behavioural studies involving dolphins are flawed and therefore not very informative. For instance, while zoologists have observed that dolphins can distinguish between the concepts "many" and "few," Manger notes: "This has also been demonstrated in yellow mealworms."
On the other hand, some bottle-nosed dolphins on Australia's west coast have learned to hold sponges over their snouts while they root around on the ocean floor. Is this a case of tool-use, indicating a high level of intelligence? Manger is skeptical. "Exactly what the dolphins do with the sponges remains unknown," he says, noting that the evidence they use them as tools is "flimsy."
Another example is dolphins' alleged talent for language. In one experiment, researchers were able to teach bottle-nosed dolphins 40 symbols. The animals were even capable of correctly interpreting combinations of the symbols, Manger admits, but African grey parrots and California sea lions can also learn this type of symbol-based language.
So is the dolphin actually the dummy of the seas? Most dolphin researchers are offended by such remarks. "To put it bluntly, most of that is bulls ," says Karsten Brensing, a marine biologist with the organization Whale and Dolphin Conservation (WDC). Manger and Gregg are losing sight of the "total package" when they compare the marine mammals' individual abilities with those of mealworms or bees, he says. "You can use similar arguments to prove that people aren't intelligent."
Lori Marino, a neuroscientist at Emory University in Atlanta, also has strong objections to Manger and Gregg's conclusions. "We shouldn't dismiss decades of peer-reviewed scientific work," she says, noting there are overwhelming indications that dolphins possess a high degree of intelligence. For instance, scientists have observed how the animals work together to encircle schools of fish. To cultivate relationships, they spoil each other with their own form of "petting" behaviour. And in a struggle for power, males will join together to form networks.
-- Der Spiegel