The burgeoning field of animal personality research seeks to figure out why individual members of a species can have so much in common, and yet be so much themselves. Natalie Angier reports that scientists have found evidence of repeated individual behaviors, preferences and personality quirks among a wide range of animals -- and that most of these animals retain their distinctive way of being through their entire lives. Researchers are "devising computer models to explain how different personality types can be maintained in a given animal population, and they are exploring the upsides and drawbacks of different personal styles."