The great Russian scientist Ivan Pavlov was one of the first to observe personality differences in the dogs he studied in his lab during the late 1800s. He could make all of them salivate at the sound of a bell in anticipation of food, but some of them just seemed to get into it more than others.
Down through the years a number of other scientists have discovered what seem to be personality traits in various animals, but the question of animal personalities has largely been ignored by science. Possibly because personality has long been considered distinctively human.
But that's changed.
"The study of animal personalities has become a hot topic in behavioral biology over the last five years or so," said Sander van Doorn, an evolutionary biologist at the Santa Fe Institute in New Mexico. He is a coauthor of a research paper published in the journal Nature that puts an evolutionary twist on the subject.
At least 60 different species, including spiders, birds, mice, fish, insects and primates, among others, have been found to have distinct personalities in the last few years.
What's particularly puzzling to biologists is similar traits, like aggression or shyness, are found in very dissimilar species, like fish and birds, but not in every member of the species, and those traits persist over a wide range of circumstances and over a long period of time. That is the very definition of personality— consistent behavior over time and in different situations.
The suggestion that animals have personalities won't come as a shock to pet lovers. Fido is a riot. Missy the cat is a bit aloof.
Yet researchers like Samuel Gosling of the University of Texas, Austin, still have trouble convincing fellow scientists.
"I get the most skepticism from scientists," he told a national science meeting a couple of years ago. "It's really the human behavior researchers who object the most."
A strong personality can be a liability in some situations. Personality is not the product of behavior. It's the other way around. Personality can lead to rigidity whereas flexibility might be more useful, especially in the wilds. So why did personality evolve among animals that would be better served by flexibility?
"That's something we're trying to explain because it's a bit puzzling," van Doorn said. "You would expect animals to be more flexible in their behavior."
The Santa Fe research is an attempt to find an evolutionary basis for the development of personalities among animals. By using computer modeling, and games designed to identify specific traits, the scientists believe they have hit on a primary principle that underlies the evolution of personality.
Animals that have a lot to lose, especially in terms of reproduction, are likely to be much more cautious in a wide range of situations than animals that have little to lose. The research shows, for example, that animals that reproduce as soon as they are able are much more aggressive and reckless than animals that spend some time, maybe even a year or so, surveying the territory first. The late bloomers will have more of a stake in the future, because they have not yet reproduced, and are thus much more cautious.
But they are also likely to be much more successful at breeding and raising their young, and thus more likely to propagate their genes.