The New York Times > Science > Looking for Personality in Animals, of All People:
[S]cientists 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.
Thanks to Carl Zimmer
. Some of the studies discussed show that different personalities are evolutionarily favored in societies, and investigate the reasons. Some are environmental, some are genetic. The same genes occur and may have similar function in humans. Very cool.