Together with Machteld Verzijden from our lab, I recently attended the annual "winter meeting" for the Association for the Study of Animal Behaviour (ASAB), close to London Zoo. The theme for this year's meeting was "Why do animals mate with the "wrong" partner?", and you can find a list of the talks here. There were several interesting talks, including contributions from Marlene Zuk about "same-sex behaviour" and Karen Pfennig about adaptive hybridization in spadefoot toads. The most interesting talk, in my opinion, was however Tamra Mendelson, who pointed out the need for a clear operational definition of species recognition, and emphasized that it should be integrated with the need for a general theory of mate recognition.
Other contributions were more controversial, including a talk by Joan Roughgarden, about the evolution of cooperation and mutual affection, and Malin Ah-King from Uppsala University about the need for developing gender-neutral models of sexual selection. Malin Ah-King took as her starting point a model based on five demographic parameters that makes no assumptions about past evolutionary history of the two sexes and argued that the so-called "w-distribution" (distribution of male-female joint fitnesses) was crucial in determining the degree of mate acceptance and promiscuity. Although I see some validity in moving away from the evoutionary psychology tradition of stereotypic sex differences to better understand mating system evolution, the opposite approach, ignoring sex differences altogether seems to be a bit too drastic in my opinion. But I might have misunderstood some underlying assumptions of this model, of course.
Even more controversial was when Ah-King suggested that we should consider alternative explanations for why animals mate than the classical evolutionary one: that animals mate because natural selection favours reproduction and the transmission of genetic material across generations. King instead suggested that animals more often mate because of "pleasure", which to me seems to be making the classical mistake of confusing proximate ("mechanistic") and ultimate ("evolutionary") explanations of animal behaviour.
As evolutionary biologist Ernst Mayr and ethologist Niko Tinbergen have taught us, proximate and ultimate explanations are not mutually exclusive, but rather complementary, and adress different "layers" in the explanation of behaviours and other traits. Thus, contrary to what Ah-King claimed, the two statements "animals mate because of pleasure" and "animals mate to maximize the transmission of their genes" are not contradicting each other. They can even be integrated by stating: "Animals have evolved pleasure of reproduction as an internal reward system because natural selection has favoured organisms which are efficient in spreading their genetic material".
This took very long time for many biologists to undertand, particularly for geneticists, physiologists and developmental biologists. There is a famous story about fly geneticist TH Morgan who, in the early twentieth century stated that: "Darwin thought that male birds had evolved bright plumage colouration because of sexual selection by female choice. We now know that this explanation was incorrect, and the reason why male birds have more bright plumage than females is because of difference in sex hormones". It would be sad if the important conceptual insights about the crucial difference between proximate and ultimate explanations, so clearly explained by Mayr and Tinbergen were forgotten again. And yet, that is the impression I got after listening to Ah-King's talk.
