The Flaw of Averages: Why We Underestimate Risk in the Face of Uncertainty

CHAPTER 39

Sex and the Central Limit Theorem

Have you ever wondered why there is sex in the first place? One theory is that animals that reproduce asexually have non-diversified immune systems. Therefore they are easy pickings for parasites, such as bacteria, which do not need to evolve much themselves to stay comfortable in their hosts. On the other hand, organisms whose genes get scrambled sexually every generation present parasites with a moving target. If this theory is correct, you would expect that one factor in selecting a mate would be to maximize the diversification of your offspring’s immune systems by adding genes unlike your own. In fact, incest is frowned upon in virtually all cultures, and scientists have shown that women prefer further genetic dissimilarities in choosing a mate. A set of genes known as the major histocompatibility complex (MHC) seems to be involved in both odor preferences and mate selection. Studies have shown that when women are asked to smell T-shirts that have been slept in for a couple of nights by men, they prefer those worn by men whose MHC genes are dissimilar to their own.¹ But even if some aspects of mate selection are in fact driven by the CENTRAL LIMIT THEORM, I still don’t recommend this term in pickup lines.

Just as investors use their money to make more money, organisms invest their genes to make more genes. But as Richard Dawkins pointed out in his 1976 book, The Selfish Gene, males and females have evolved with very different biological ...