As I write in the “Afterplay” of my book, “The charge of penis staring and vagina neglect should certainly be taken to heart by the whole field of genital science.” I argue that, partly for practical reasons, but partly also because of cultural bias, the evolutionary biology of genital research has focused too much on male genitals and too little on the female side of things. This may be dangerous, because if we assume that the diversity is mostly on the male side, this may lead us to think that the evolution is driven more by cryptic female choice rather than sexually antagonistic coevolution. Now, a paper in PLoS Biology has appeared that tackles this matter more seriously and quantitatively. Malin Ah-King, Andrew Barron and Marie Herberstein studied the scientific literature on genital evolution over the past 25 years and scored how many were only on male genitalia, how many only on female ones, and how many focused equally on both. Out of the 364 papers, they found that 48.6% (177) were on male genitalia, only 7.7% (28) on female genitalia, and 43.7% (159) on both male and female genitalia. Although they acknowledge that this consistent male bias may be partly due to practical reasons, they favor a scientific-cultural bias as the explanation, because (a) with modern CT-scanning techniques the practical obstacles no longer exist, (b) the bias is present in female as well as male authors. They also point out that the degree of bias appears to differ between the types of animals being studied and the kind of questions being asked, further reinforcing the notion that tradition, rather than common sense, steers the focus on male genitals.
Overall, I think the study by Malin et al. reveals what is going on. The desire to fit within an ongoing research trend and to “do what everybody else has also been doing” probably causes much of the bias. On the other hand, I feel that the authors downplay the practical considerations too much. It is not just about accessibility of the female genitalia (often soft and invaginated and hard to dissect and image) but also the lack of prior knowledge. If you want to pay equal attention to the male and female genitalia in a particular kind of animal, then it can be daunting to have to start from scratch for the one sex, while for the other sex there is already a whole literature and terminology available. However, having said that, I do agree that this is not an excuse. Genital researchers must clean up their act and pay both sides of the sexual divide equal attention. Only then can they be sure not to overlook important information. And, as I told Alan Boyle of NBC News, “Being aware of it is part of the remedy.” This is where the study by Malin et al. has done us a favor.