He drew a waspish parallel between the English aristocracy and rare parasitic ants, which rely for protection by exploiting the social instincts of the host colony while contributing little to the colony's good. To quote Fisher, 'In human societies man is his own parasite, a circumstance which seems to ensure that all civilised societies shall be fully infested'. Fisher analysed large bodies of data and concluded that differences in fertility were enormously important in driving human evolution. He also made the astute observation that 'infertility is an important cause of wealth'. I'm going to suggest that not only is a certain degree of subfertility built in to the way we've evolved, but that from the perspective of the human species as a whole it may not be such a bad thing.
Humans are remarkably infertile compared with any other animal.
Men in particular, sit at the bottom of the league table for just about every criterion. One measure of fertility, for example, is the number of sperm produced per unit mass of testis. But mice are selected for fertility', I hear you say. Humans have never been selected for fertility, in fact quite the opposite. We are almost unique among mammals in having a genetically programmed period of infertility built into our life cycle, in the menopause.