Everyone who's owned a pet knows that animals have personalities. When I read this I thought
about cats and dogs, but the article says that personalities have been identified in over 60 species, including fish, insects, and mollusks. Scientists are looking into how these personalities might have evolved. The article says that in many cases, personalities are shaped by how much an animal has to lose (in terms of reproduction), and the more an animal has to lose, the more cautious it will tend to be over time and in many situations. The scientists present two observations: variations among personalities are often structured around willingness to take risks, and secondly, individuals often have to choose between reproducing now or later. (Reproduction now diminishes resources for future reproduction.) The researches came up with a mathematical model of how this decision creates populations where some choose to reproduce later, while others choose to reproduce now. Those who choose to reproduce later are less risky in their activities, whereas those tho reproduce now are willing to take more risks. This could be an explanation as to why different individual animals display different personalities.
Also here is my book review of Gould's Rocks of Ages. Just be glad I read it so you didn't have to!