MUNSTER — Beyond genetics, no rabbit is truly like any other whether in the wild or as a house pet. Every animal has its own character that develops along the same lines as human character. Recent studies show that the closeness a rabbit shares with its parents, and whether or not it gets along with siblings or views them as rivals, help determine the animal’s character later in life. The same holds true for rats, whose personalities also develop along the same line as human personalities.

Researchers working with Aron Tulogdi at the Budapest Institute for Experimental Medicine and published in Developmental Psychobiology tried to make aggressive rats more placid. These very social animals turn aggressive when they spend their childhood in isolation. Could this be reversed if they later were raised with other rats?

To find out, the researchers put three-week-old rat babies alone in cages. That left behavioral traces on the animals: The rats that had grown up in isolation turned out to be aggressive, displayed anxiety when they were put in cages with other rats and slept apart from them. This behavior is strikingly similar to that of humans who have experienced troubled childhoods.

But within a few days in a group, something changed in the behavior of the rats brought up in isolation. Very soon they were bedding down for the night with the other animals — although they remained more aggressive than rats that had been socialized normally. Once again researchers found astonishing parallels: In human behavior, while social phobias can be treated with a high degree of therapeutic success, this is more difficult when it comes to aggressive behaviors.

Pecking order

Uncanny similarities such as these are emerging ever more strongly from animal behavioral research. "We develop hypotheses that in many regards could apply to human beings," Norbert Sachser, professor of behavioral biology at the University of Münster, says. "Although human characters are of course significantly more complex, our brains follow basic patterns that are similar to those of animals."

In this way, early ties mark the nature of both animals and humans. The relationship of a person to his or her parents and siblings is decisive when it comes to the character that person develops. The same goes for animals: Their relationships to family members determine their personality development, says Sachser.

Rats who did not receive loving maternal care were more susceptible to stress. But other factors come into play as well: "With animals, even siblings play a role in behavior profile," he says.

That is confirmed by research done at the University of Bayreuth and the University of California (Behavioral Ecology, online). Researchers showed that in behavioral tests, wild rabbits that weighed a lot at birth were braver and more curious than lighter siblings from the same litter. That held true months later when the weight of the animals had evened out.

One of the possible reasons for this, according to researchers, is the division of roles in the rabbit family. In games and pecking-order contests, the heavier newborns won more often than their lighter siblings did. They thus presumably developed more self-confident character traits that stayed with them as they got older, whereas the lighter, weaker baby rabbits had to deal with more setbacks and thus remained somewhat anxious.

Are there possibly other decisive phases in the personality development of rats and rabbits? "There are indications that personality can be marked throughout puberty," says Sachser.

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