Sexual Diversity in the Animal Kingdom

Brie McLemore

A Different Interpretation of Sexual Characteristics, Sexual Selection, and Homosexuality In An Evolutionary Context

In Sexual Diversity in the Animal Kingdom, Dr. Joan Roughgarden establishes a different concept of sex that disputes traditional perceptions of a biological binary within the animal and plant kingdom. Through this analysis, Roughgarden is also able to challenge the prevalent assumptions of sexual selection as presented by Charles Darwin, in which females are described as coy and, in contrast, males are described as active. By presenting examples of sex role reversal and homosexuality in multiple animal species, Roughgarden is able to decouple the traditional correlation between mating and sexual reproduction. Instead, Roughgarden establishes social cooperation as an important mechanism of sexual reproduction that requires participation from all community members.

Traditional conceptualizations of sexual characteristics in a biological context have posited the classifications of females as those who possess larger gametes (the oocyte), and males as possessing smaller gametes (sperm). This concept has resulted in a theory of sexual selection in which women are presumed to be coy, or more selective in their mating partners, due to the high cost of reproduction for women. In comparison, males, due to their low cost of reproduction, are presumed to be more promiscuous in order to produce more offspring that will survive to the next generation, therefore making them more fit. Roughgarden asserts that these fixed “templates” have been interpreted as empirical and universal claims that are then applied to all animals, humans included. However, by observing many different animal species, Roughgarden has been able to challenge perceptions of a sex binary in biology.

Roughgarden maintains that there are multiple examples of sex role reversal that challenges Darwin's theory of sexual characteristics. Star fish and pipe fish, for example, are fish species in which females have a low cost for egg reproduction, and, therefore, mate with many males while males, on the other hand, have the duty of caring for the children. This implies that traditional perceptions of females as caring and nurturing, which is implied by their maternal roles, is not evident in all animal species. Also, these examples provide examples of how men are not always promiscuous in attempts to simply spread their seed, but are also concerned with their offspring's well-being and actually do, in fact, have a high cost of reproduction.

Roughgarden also challenges the traditional perceptions of sexual roles in biology due to the prevalence of asexuality or multiple sexes within the animal kingdom. Jacana birds, for example, are a select bird species in which there are three male genders who each fulfill a certain role within reproduction. These examples serve as challenges to traditional perceptions of fixed and universal sex roles that have been widely accepted throughout biology. Since Roughgarden has seeks to dismantle the sex binary, sexual selection theory, as a result, must also be challenged. If sexual characteristics in the animal kingdom actually exists as part of a broad spectrum then so much sexual selection.

Roughgarden presents, as an opposing theory to Darwin's sexual selection, that social cooperation as what necessitates sexual reproduction. In this theory, friendship, not competition is the basis for a social system in which children are raised. In the film, Roughgarden questions whether sexual selection in the animal kingdom has even taken place. She asserts that, if sexual selection was in fact taking place, after twenty generations all males would be the same. The “bad” genes would be eliminated from the gene pool, thus no longer requiring females to choose quality mates.

Roughgarden examined extra-parent paternity in many bird species in order to disprove the “good gene hypothesis.” Although monogamy is prevalent in many bird species, there is an overwhelming presence of eggs being nurtured by all neighboring males, even those that aren't the father. For some bird species, many males will nurture children when paternity is not even evident. Shared maternity is also popular due to eggs being laid and nurtured by adjacent females. These examples discredit the “good gene hypothesis,” because they provide instances in which multi-parenting takes place, making “fitness,” as it is commonly understood, irrelevant. In these instances, both males and females are concerned with the offspring within their community, not strictly their own. Since males and females alike work together to ensure survival of all offspring, mating with strictly those who acquire “quality” genes is insignificant. In these cases, females do not experience limited resources in reproduction. Instead, males and females negotiate in order to optimize reproduction.

By postulating a theory that focuses on the role of social cooperation within biological reproduction, Roughgarden is able to interpret and analyze the function of homosexuality in animals, that was before discredited. Due to the traditional interpretation of sexual selection, homosexuality was treated as a misnomer, and even an evolutionary deterrent because it could not result in offspring. However, Roughgarden is skeptical of this speculation due to the overwhelming presence of same-sex sexuality within animal species.

Roughgarden asserts that homosexuality can no longer be understood as a deleterious trait in an evolutionary context due to it's commonality. In Darwin's theory of natural selection, traits that are deemed “unfit” prohibits an affected individual from surviving in their environment. As a result, these traits become less prevalent in later generations since those inflicted with the disorder do not survive long enough to reproduce. Traditionally, homosexuality has been considered a mutation due to the inability to reproduce of gay individuals. However, Roughgarden theorizes that understanding same-sex relations in this way is problematic and false. If homosexuality were in fact a deleterious mutation, it's output would be a detriment to fitness. Roughgarden calculates the deleterious effect of homosexuality on fitness to be .01%, which is minimal at best. This is evident by the fact that non-deleterious traits persist throughout generations, as is evident with homosexuality. Also, Roughgarden asserts that homosexuality is adaptive since, even if it were eliminated, it would resurface.

With her new interpretation of sexual selection, Roughgarden is able to provide an understanding of homosexuality within a biological reproductive context. Homosexuality, Roughgarden states, achieves teamwork within a community as members who participate in same-sex relations work towards a common goal, physical intimacy and pleasure. Homosexuality challenges perceptions that animals, and humans alike, are always competing and striving towards reproduction. In Roughgarden's different understanding, social cooperation of both males and females is utilized to increase reproduction and fitness for all offspring within a community. This framework allows for an understanding of homosexuality, not as a detriment or challenge to fitness, but as an essential aspect of social cooperation that is beneficial to reproduction and the raising of offspring.