The resulting book, Evolution’s Rainbow, was an audacious attack on Darwin’s theory of sexual selection. To make her case, Roughgarden filled the text with a staggering collection of animal perversities, from the penises of female spotted hyenas to the mènage à trois tactics of bluegill sunfish. As Roughgarden put it, “What’s coming out [in the past 10-15 years] is to the rest of the species what the Kinsey Report was to humans.”
According to Roughgarden, classic sexual selection can’t account for these strange carnal habits. After all, Darwin imagined sex as a relatively straightforward transaction. Males compete for females. Evolutionary success is defined by the quantity of offspring. Thus, any distractions from the business of making babies—distractions like homosexuality, masturbation, etc.—are precious wastes of fluids. You’d think by now, several hundred million years after sex began, nature would have done away with such inefficiencies, and males and females would only act to maximize rates of sexual reproduction.
But the opposite has happened. Instead of copulation becoming more functional and straightforward, it has only gotten weirder as species have evolved—more sodomy and other frivolous pleasures that are useless for propagating the species. The more socially complex the animal, the more sexual “deviance” it exhibits. Look at primates: Compared to our closest relatives, contemporary, Westernized Homo sapiens are the staid ones.
Despite this new evidence, sexual selection theory is still stuck in the 19th century. The Victorian peacock remains the standard bearer. But as far as Roughgarden is concerned, that’s bad science: “The time has come to declare that sexual theory is indeed false and to stop shoe-horning one exception after another into a sexual selection framework…To do otherwise suggests that sexual selection theory is unfalsifiable, not subject to refutation.”
Roughgarden is an ambitious scientist. She believes it is impossible to comprehend the diversity of sexuality without disowning Darwin. Although she isn’t the first biologist to condemn sexual selection—Darwin’s theory has never been very popular with feminists—she is unusually vocal about cataloguing his empirical errors. “When I began, I didn’t set out to criticize Darwin,” she says. “But I quickly realized that most scientists are pretty dismissive about same-sex sexuality in vertebrates. They think these animals are just having fun or practicing. As long as scientists clung to this old dogma, homosexuality would always be this funny anomaly you didn’t have to account for.”
Roughgarden’s first order of business was proving that homosexuality isn’t a maladaptive trait. At first glance, this seems like a futile endeavor. Being gay clearly makes individuals less likely to pass on their genes, a major biological faux pas. From the perspective of evolution, homosexual behavior has always been a genetic dead end, something that has to be explained away.
But Roughgarden believes that biologists have it backwards. Given the pervasive presence of homosexuality throughout the animal kingdom, same-sex partnering must be an adaptive trait that’s been carefully preserved by natural selection. As Roughgarden points out, “a ‘common genetic disease’ is a contradiction in terms, and homosexuality is three to four orders of magnitude more common than true genetic diseases such as Huntington’s disease.”
