The arcs of evolutionary genetics always cross back

If you have more than a marginal interest in evolutionary biology you will no doubt have stumbled upon the conundrum of sex & sexes. Matt Ridley's most prominent work, The Red Queen: Sex and the Evolution of Human Nature, covered both the theoretical framework and applied implications of the subject. Ridley leaned heavily upon William D. Hamilton's scientific work, which extended upon Leigh Van Valen's concept of the book's titular Red Queen. The complex interplay between pathogens & multicelluar organisms across the eons is a topic of such breadth and depth that a substantial proportion of the territory in evolutionary biology is still devoted to it, and how sex may relate this dance. Hamilton spent the second half of his career focusing on just this question, outlined in Narrow Roads of Gene Land, volume 2 of his collected papers.* The question of sex begins with a simple self-evident curiosity: why not cloning? Assume that you are a creature who can be expected in any given generation to have two offspring reach maturity. Imagine two populations, one clonal and purely female and another sexual with females and males. In the later case let us assume a 50:50 sex ratio (this does not always occur, but often does for a peculiar evolutionary genetic reason). All things equal the former population should be able to produce twice as many offspring for subsequent generations. Males are a waste of a body, a "vehicle" as Richard Dawkins would say. Instead of producing offspring the bodies of males serve as halfway houses for genes. Consider the circumscribed lives of drones among the hymenoptera. An answer may be that if men are a plague upon women, they may also offer women a salvation from plagues. The evolutionary psychologist Geoffrey Miller constructs a speculative illustration of this principle in The Mating Mind, while the behavioral ecologist Bobbi S. Low reports on more concrete cases in Why Sex Matters. Why patriarchy? One must always engage the pathogens which inevitability threaten to turn into the bane of a multicellular organism's existence. These are big questions, but fleshing out the details can only be done case by case. Though there are some ethnographic and biological anthropological research programs attempting to tease apart the nature of the relationship between disease load and sexual behavior, there are obvious limits to this sort of work. Humans are big slow breeding organisms constrained by ethical considerations. At the other extreme are those who play with parameters in silico (much of Hamilton's later theorizing was in simulation and not analysis). To split the difference one might look to fast reproducing model organisms, attempting to draw general inferences from specific results. That is what a letter to Nature attempts to do in relation to sex, or more accurately sex with self or non-self, Mutation load and rapid adaptation favour outcrossing over self-fertilization: