I’ve explained in a little detail how female selection can cause runaway growth, as in a peacock’s tail or, as it turns out, a human brain. I’m just going to take a few minutes today to explore one more aspect of the math behind runaway selection.
In most sexually reproducing species, there is really no such thing as a “female gene” or a “male gene.” That is, both females and males have the same genes, but they express differently depending on the sex of the individual. To borrow an example from Richard Dawkins in The Blind Watchmaker, if you are female and your father has a very big penis, you are likely to have the genes for a very big penis, but since you are female, there will be no outward sign that you carry this gene. It is dormant, or is busy doing something else that only applies to females. (If there are any geneticists reading this, forgive me for simplifying it so much.) However, if you have a son, there is a good chance that he will inherit from you the gene for a big penis. We see this all the time, and in fact, when we are in polite company and are not speaking of genitalia, we often say that a boy resembles his maternal grandfather. Intuitively, we all know this principle.
What isn’t so obvious is that this principle is one of the driving forces behind female sexual selection. It also helps us to explain another human trait that we all recognize but perhaps have never considered as instinctive and evolutionary. To put it simply, genes for traits and genes that make us prefer those traits are passed down in the same way. In other words, if a particular generation of peahens mate with the peacocks with the biggest, brightest tails, this trend will only continue if the daughters also prefer to mate with the same kind of males. Female preference must be just as genetic as the physical traits of the males. To put it into human terms, if my father was short and stocky, then my mother probably has a genetic tendency to prefer short stocky men. If I have a daughter, it is likely that I will pass on the genes for preferring short stocky men, even if I happen to be a tall and lanky man. In a very real sense, when two people reproduce, they are passing on genes for preferring to reproduce with people just like them. It’s well beyond the scope of this blog (and of my ability to communicate complex math) to explain why this is mathematically necessary for runaway selection to work, but it is, and runaway selection works. While some minor details may not be all worked out, it is certain that female preference must also be passed down through males. *
This should give us a moment’s pause. It is no coincidence that women often compare their husbands to their fathers. It is no coincidence that daughters of abusive fathers often marry abusive men. I must temper this observation with a warning, though. It would be wrong to suggest that these tendencies are “entirely genetic” just as it would be wrong to say they are “entirely environmental.” In modern evolutionary science, the distinction between environment and genes is so blurred as to be almost unintelligible. That is, genes express through their environment and the environment “expresses” through genes. The “nature vs. nurture” debate, for all intents and purposes, is dead. Neither side won because there was never a distinction to be made in the first place. The harsh reality is that if you are attracted to abusive men, your daughter, regardless of the environment she grows up in, is likely to inherit the gene in you that gave you the tendency to respond to your environment in the way you did. Furthermore, having a son will not stop the process. His daughters are also quite likely to carry the same gene.**
Now, I must warn the reader that I am about to indulge in some self-congratulatory moral pronouncements. They should be taken with a grain of salt, but I hope you will consider them nonetheless. I feel that knowledge of the science of humanity comes with the price of moral obligation. For instance, women who find themselves continually attracted to abusive men are responsible to their potential children, grandchildren, and great-grandchildren. They must ask themselves whether or not it is justifiable to continue to pass on the genetic preference for such men. I will not be taking the time in this particular blog to demonstrate just how clearly behavioral tendencies are linked to genes, but for any curious readers, I would recommend this book: