Looking for Personality in Animals, of All People

By CARL ZIMMER
New York Times
March 1, 2005

A team of Dutch scientists is trying to solve the mystery of personality. Why are some individuals shy while others are bold, for example? What roles do genes and environment play in shaping personalities? And most mysterious of all, how did they evolve?

The scientists are carrying out an ambitious series of experiments to answer these questions. They are studying thousands of individuals, observing how they interact with others, comparing their personalities to their descendants' and analyzing their DNA.

It may come as a surprise that their subjects have feathers. The scientists, based at the Netherlands Institute of Ecology, are investigating personalities of wild birds.

Until recently, most experts in personality would have considered such a study as nothing but foolish anthropomorphism. "It's been looked at with suspicion and contempt," said Dr. Samuel Gosling, a psychologist at the University of Texas.

But scientists have found that in many species, individual animals behave in consistently different ways. They argue that these differences meet the scientific definition of personality.

If they are right, then human personality has deep evolutionary roots. "It's a matter of degree, not of differences," said Dr. Piet Drent of the Netherlands Institute of Ecology.

The bird study that Dr. Drent and his colleagues are conducting is considered the most ambitious investigation of personality in wild animals.

"They've gone the furthest," said Dr. Sasha Dall, an evolutionary biologist at the University of Exeter in Cornwall.

The Dutch researchers are studying the importance of genes to the personalities of the birds, and the effect different personalities have on their survival. They hope next to carry out parallel studies in humans to see whether the same forces behind the evolution of bird personalities are at work in our own species.

The science of human personality is about a century old. Psychologists have relied largely on questionnaires and other testing methods to map out its dimensions. One common method is for scientists to ask their subjects how well certain adjectives apply to themselves (or to people they know well).

"Certain traits tend to go together," Dr. Gosling said. "We find that people who are energetic also tend to be talkative. It needn't be that way, but that's how it tends to be." The flip side is true as well: less energetic people tend to be less talkative.

Psychologists have found they can bundle these traits into just a few personality dimensions. People may be more or less extroverted, for example, which means they are sociable, assertive and tend to have positive emotions. The same dimensions have been documented across the world, from Zimbabwe to the Russian Arctic, suggesting that they are universal in humans.

Some studies have suggested that genes are responsible for some of the differences in people's personality ratings. But they have been far from conclusive because scientists cannot do experiments with humans. "Human mothers will not let you just swap their infants at birth, which would be a great study to do," Dr. Gosling said.

It has been only in the last decade or so that scientists have investigated whether animals have personalities. In one pioneering study in the mid-1990's, Dr. Gosling studied a colony of 34 hyenas at the University of California, Berkeley. "My goal was simply to say, can we measure personality in animals? It wasn't clear it was going to work," he said.

Dr. Gosling asked the four caretakers of the colony to fill out a modified version of the human questionnaire for each animal.

"It turned out that they agreed at the level you find in humans," Dr. Gosling said. What's more, the hyena personalities fit some of the dimensions found in humans, like neuroticism and agreeableness. Since then, a number of other studies have documented personalities in animals ranging from chimpanzees to squid.

To some biologists, the main question about these animal personalities is why natural selection keeps such a wide range of them. "Why hasn't one personality become the standard in the population?" asked Dr. Drent. If being extroverted offers the best odds for a hyena to reproduce, you might expect that over time, all hyenas would wind up as extroverts.