The Collegian

Issue date: 3/27/07 Section: News

Media Credit: Annie Douglass

On March 23, Dr. Joan Roughgarden came to Saint Mary's from Stanford to stir the scientific water by attacking Darwin's theory of sexual selection. The sexual selection theory says some male animals develop physical attributes apparently detrimental to everyday survival for the purpose of impressing females. One cited case was the peacock's tail. Darwin's theory has been generally accepted for almost 150 years, but is now facing skepticism from Dr. Roughgarden and other members of the scientific community on several points.

Dr. Roughgarden's first issue with Darwin's theory of sexual selection was its basis in the "male-female binary." In science, the male-female distinction is determined by the size of gametes produced. The sex which produces small gametes is male, and the sex which produces large gametes is female. The problem, according to Roughgarden, arises in assuming each species has one set of males and one set of females. She said the most common biological plan in nature is one in which a single organism is both male and female at the same time, or else is sometimes male and other times female.

Darwin's theory, she said, is based on a specialized case in which one organism is the same sex its entire life, an attribute rare in the biological world. Roughgarden claimed this negates the issue of attracting a mate of the opposite sex, since in some species there is no opposite sex.

Roughgarden's next issue was Darwin's assumption that there is only one type of male and one type of female in each species. She particularly cited blue sunfish and European ruffs as species in which this is not the case. In each of these species, there are three types of males, each distinctly different in coloring, size, and other physical attributes, but each with a relatively equal chance of being able to breed with females. She said this shows that single aspects of physiology cannot account for selection, since each type of male is entirely different.

Roughgarden next pointed to data from a 24-year study of over 8,500 birds to refute Darwin's theory. She said the data shows that even where Darwin's theory should work, it does not. This particular set of birds meets all the qualifications of Darwin's theory, including, male-female binary, separate sexes for entire life, and a particular flashy feature in the male believed to account for sexual selection. Through statistical data analysis, it was shown that there is no correlation between the flashy attribute and an individual's chance of being chosen for mating.

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