In general we humans like to put concepts into categories and make rules to help us understand the world around us. We then focus on the rules and not the exceptions to the rule, but in science not focusing on the ‘whole picture’ can lead to biases in research. Malin Ah-King, a gender researcher and evolutionary biologist at Uppsala University in Sweden, recently gave a seminar about the gender biases involved with sexual selection theories that demonstrates the problem of excluding the “exception”.
Sexual Selection Development
In the 1800’s Charles Darwin observed animals such as the male peacock displaying his magnificent plumage to the female and the seeming male superiority in humans. He theorized that to maximize their own reproductive success, males are sexually selected to be dominant and females are sexually selected to be passive or “coy.” This theory of sexual selection was later enhanced by geneticist Angus J. Bateman in 1948. His study on the offspring of mated fruit flies led to what is now considered male-male competition and female choosiness – two components of sexual selection. Male-male competition is the competition between males in order to have the best reproductive success. Female choosiness is the preference of females for males with certain traits and/or behaviors. Along with male-male competition and female choice as part of sexual selection is anisogamy. Anisogamy is the fusion of a small (male) gamete and a large (female) gamete, which can be an identifier of gender. Once gender is determined, it can then be expected each sex will fit into their “role” of sexual selection.
What was originally started by Darwin and expanded on by Bateman has established today’s current views and understanding of sexual selection and gender. This Darwin-Bateman Paradigm is based on the following assumptions:
- Male reproductive success (fitness) is more variable than females
- There is a higher benefit of male multiple mating than for females
- Males are generally more eager to mate and relatively indiscriminate whereas females are less eager and more discriminating
These assumptions may be the supposed rule, but what about the exceptions? Ah-King pointed out that this is a very narrow sense of sexual selection and that this theory does not take into account reproductive success by chance, nor the role of female variations.
The Switch-Point Theorem (SPT) is an alternate theory of sexual selection that is a gender-neutral model. This model includes the possible random or chance effects that may be involved in reproductive success that was not included in the Darwin-Bateman Paradigm. SPT predicts behavior on 5 parameters: survival probability, encounter rate, latency, population size, and w-distribution (theoretically what would happen if all males and females mated). These predictions demonstrate that random or chance effects do influence reproductive success. Unfortunately, this alternative theory has not been tested and is often overlooked. Even if SPT predictions were confirmed, it is likely that current views of sexual selection would still be based on the Darwin-Bateman Paradigm.
Sex is a Reaction Norm
Ah-King takes a different approach at looking into male and female differences. Her research supports that sex is a reaction norm. A reaction norm in this sense is the wide range of physical characteristics or traits that a genotype can create, in response to different environmental conditions. Essentially this means that sex can be flexible aside from anisogamy where the gametes are associated with the male and female. Some examples of how these other characters and features vary are found in a wide variety of species.Turtles, for example, have temperature dependent sex determination demonstrating the influence of the environment.
Sexual behaviors and roles may also vary such as the female competition that occurs in a species of gobies, or the parental Sexual characters can also be quite variable including genital morphology. In humans there are many examples of feminine men or masculine women such as a bearded woman. All of this variability demonstrates that sex is not as fixed as we tend to think of it and is actually quite flexible.care in seahorses and penguins.
Historically gender bias has always focused more on the male which has no doubt greatly influenced the theory of sexual selection and corresponding research. The Darwin-Bateman paradigm, although biased, is still what dominates views today and as a result other theories such as SPT and Ah-King’s research can be overlooked and misinterpreted. By ignoring these “exceptions” to the rule today’s research could have a major gender bias. Ah-King hopes that by increasing awareness of these biases we may be able to find ways to address them.
- Sex in an Evolutionary Perspective: Just Another Reaction Norm; Ah-King & Nylin, 2010
- The Darwin-Bateman Paradigm in Historical Context; Dewsbury, 2005
- Female sexual selection in light of the Darwin-Bateman paradigm; Ah-King, 2011
- On anisogamy and the evolution of ‘sex roles’; Ah-King, 2013
- Role reversal: adult sex ratio leads to ‘gender-bending’ birds; Griffith, 2013
- Male parental care, differential parental investment by females and sexual selection; Moller & Thornhill, 1998
- The still-tolerated gender bias in science; TED blog
- Video of sexual selection example with birds of paradise