[Paleopsych] NYT: Looking for Personality in Animals, of All People
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Sat Apr 16 22:06:56 UTC 2005
Looking for Personality in Animals, of All People
By CARL ZIMMER
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
"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
Dr. Drent and his colleagues hope that their study on birds may reveal
some clues. They are studying a European relative of chickadees called
the great tit (Parus major). Most of the birds spend their entire
lives in a single forest, and they are happy to move into comfortable
nest boxes provided by the scientists. As a result, the Dutch
researchers can track the entire population of birds for years,
keeping tabs on their health and their success at reproducing.
The scientists can also bring some of the birds into the lab in order
to measure their personalities or carry out breeding experiments.
"These birds are perfect for these sorts of studies," said Dr. Niels
Dingemanse of the University of Groningen, a collaborator Dr. Drent.
Instead of questionnaires, the Dutch team tests the behavior of the
birds to measure their personalities. In one test, the scientists
place a strange object - a penlight battery or a Pink Panther doll -
in a bird's cage. Some birds are quick to approach it, while others
In another experiment, the researchers open a cage door, allowing the
birds to explore a large room filled with five artificial trees. Some
birds are quick to explore the trees, while others prefer to remain in
the comforts of their cage.
In a third experiment, the researchers place a bowl of tasty mealy
worms in the room. When the birds land on the bowl to eat, the
researchers startle the birds by lifting up a nearby metal plate. They
then see how much time passes before the bird returns to the bowl.
The tests revealed that the birds have consistent personalities that
remain stable for years. Bold birds, as the scientists call them, are
quick to inspect new objects, to explore the trees and to recover from
the metal-plate surprise.
Shy birds are slow on all three counts. The differences go well beyond
these tests. Bold birds are also more aggressive than shy ones and
experience less stress when the scientists handle them.
Breeding experiments revealed that these traits had a strong genetic
basis. Over just four generations, the researchers could produce
significantly bolder and shyer birds. "About 50 percent of the
variation you find in avian personalities is due to differences in
genes," said Dr. Kees van Oers of the Max Planck Institute for
Ornithology in Germany.
Dr. van Oers is searching for the genes responsible for these
differences. He estimates that as many as 10 may play an important
role, and he has already pinpointed one strong candidate, known as
Some studies on the human version of this gene suggest that it
influences how much people seek out new experiences. But other studies
have failed to replicate the link. "We're still working on the last
bits, but it looks promising," Dr. van Oers said.
The genes for both bold and shy traits have been preserved by natural
selection. To find out how this happens, the researchers have observed
how birds with different traits have fared over the years. "We were
not sure how the data would turn out because no one had collected them
before," said Dr. Dingemanse, who led this part of the study.
The researchers found that the personality of birds had a powerful
effect on their survival, but that effect changed from year to year as
the supply of food fluctuated. "It's quite a complex story," Dr.
Dingemanse said. In lean years, for example, bold female birds had a
better chance of surviving than shy ones, while shy males did better
than bold ones. Those patterns switched during years with abundant
Over the course of several years, however, birds with intermediate
personalities appear to have had more success at bearing young.
"Animals in the middle did better," Dr. Dingemanse said.
If intermediate birds are better adapted than very bold or shy ones,
it is strange that all the birds are not intermediate. One possibility
is intermediate personalities arise when birds inherit a "bold"
version of certain genes from one parent and a "shy" version from the
Since a bird has a 50 percent chance of inheriting a gene from its
mother or father, it's inevitable that some will wind up with two
"shy" genes or two "bold" ones. As a result, they may get extreme
Another idea the Dutch scientists want to explore is that the social
life of birds helps bold and shy personalities to coexist.
Each year the birds fight for territory where they can feed and breed.
Bold birds are more aggressive than shy ones, and that sometimes helps
them win territory. But the scientists have found that when bold birds
lose, they are slow to recover. They end up at the bottom of the
hierarchy, and in many cases just fly away. "They go to other places
to try to become No. 1," Dr. Drent said.
This struggle might balance the birds between bold and shy
personalities. If there are a lot of shy birds, the few bold ones will
rise to the top. But if there are a lot of bold birds, they will fight
a lot, and that will result in a lot of bold birds flying away. In
these cases, the few shy birds will thrive. "So one of the
personalities can never disappear completely," Dr. Drent said.
He and his colleagues plan to test this hypothesis by altering the
ratio of bold and shy birds in the wild.
Many of the findings are summarized in the February issue of
Neuroscience and Biobehavioral Reviews.
Researchers studying animal personality hope that their work will
yield some practical benefits. Dr. Gosling and his students, for
example, have been focusing much of their research on the
personalities of dogs.
An accurate test of dog personality may help animal shelters match
pets to families. It may also help identify dogs that are especially
well suited to jobs like detecting explosives.
Studies on animal personality may also illuminate human personality.
The Dutch researchers are now beginning to compare their research on
birds to research carried out on children.
"It was amazing how the way they measured the boldness of the birds
resembles tests we have for young children," said Dr. Marcel van Aken,
a psychologist at the University of Utrecht. He and the bird
researchers plan to measure the personalities of birds and humans with
a common set of tests, hoping to find clues to the evolution of human
Barely any research has been carried out on the evolution of human
personality, but what little there is suggests that it may have some
parallels with what's happened in birds.
In a survey of 545 people, Dr. Daniel Nettle of the University of
Newcastle in England found that the more extroverted people were, the
more sex partners they tended to have had. That might give them an
evolutionary edge, but Dr. Nettle found that they were also more
likely to wind up in a hospital.
Dr. Nettle is reporting his findings in a paper to be published in
Evolution and Human Behavior.
Some experts on human personality remain skeptical. Dr. Daniel Cervone
of the University of Illinois at Chicago considers describing animals
with terms like extroversion as "extremely risky." The word inevitably
means something different when applied to a human or a bird.
"There's a whole load of human qualities that simply weren't going
into the ratings in the first place," he said.
Dr. van Aken agrees that anthropomorphism is a real danger, but he
thinks it can be avoided. "I'm not so concerned about it," he says.
"You have to define clearly what you are going to measure and then let
the data speak."
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