Animal Sexuality; January 1994; Scientific American Magazine; by Crews; 7 Page(s)

One of the most fundamental characteristics of life is sexuality, the division into male and female. Sexual considerations influence the appearance, form, behavior and chemical makeup of nearly all multicellular organisms. Amazingly enough, scientists cannot conclusively say why sex exists. In recent years, however, animal studies have provided a great deal of information about the multifaceted components of sexuality. These studies reveal that many familiar aspects are less universal than once supposed. The work provides a new framework for understanding the relationship between males and females and a glimpse at how sex evolved.

Among vertebrate animals, sexuality is expressed in a number of ways. Males and females exhibit a wide variety of chemical, anatomic and behavioral disparities. The most obvious of the behavioral divergences lies in an animal's copulatory activity. In general, individuals having testes attempt insemination (male-typical behavior), whereas individuals having ovaries are receptive to being inseminated (female-typical behavior). Males and females often differ in other, less overt ways, such as level of activity, regulation of body weight, level of aggression and learning patterns. Some gender-specific actions are associated with, but not necessarily caused by, systematic dissimilarities in certain parts of the brain.