Why do males and females frequently differ in body size and ...( RIVERSIDE Calif. As even the most c...)

RIVERSIDE, Calif. As even the most casual observer of nature knows, males and females frequently differ in body size, form and structure. But how these differences have developed a topic studied for decades by evolutionary biologists is not as clear.

A new scholarly book now neatly brings together the latest research findings in evolutionary biology that can help explain gender differences in a variety of organisms, including mammals, birds, reptiles, amphibians, insects, spiders and flowering plants.

"Sex, Size & Gender Roles: Evolutionary Studies of Sexual Size Dimorphism" (Oxford University Press, 2007), edited by UC Riversides Daphne Fairbairn and two others, is a compendium of 20 chapters that together address intriguing questions such as why males tend to be larger than females in many large mammals, while females are generally the larger sex in smaller animals such as insects and spiders.

The book also delves in depth on how differences between the sexes can evolve in spite of substantially identical genetic material.

In all species with separate sexes, males and females are striving to maximize their genetic contributions to future generations, but the ways of doing this vary enormously among species, said Fairbairn, a professor of biology. We see this reflected in fantastic patterns of sexual dimorphism that we have only begun to appreciate.

The book includes numerous examples of gender differences seen in nature. For example, why female spiders are often much bigger than male spiders, and why in deer and sheep the opposite is usually true.

According to Fairbairn, who also wrote two of the book's chapters, male spiders, by being small, are adapted for searching for widely-dispersed females, while the females rema
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