Debate: The Evolutionary Basis of Sexual Depravity

Paul from Reasonable Doubt and I are debating Christian sexual morality.

1. Paul's Opening. Points to various laws regulating consensual behavior in the bible.
   
2. My rebuttal
   

1. My opening. The evolutionary defense of sexual depravity.
   
2. Paul's rebuttal
   
3. My closing
   

He brings up many topics but I would like to focus on what I take to be the most important: abstinence and marriage. Paul writes:

Let's start with a really simple truth - sex is not a bad thing. Moving on, sex between consenting adults is not a bad thing. More importantly, sex between consenting adults is not my business, not your business and, unless you are god not for you to judge.

I agree that sex is a good thing – but only within the context of lifelong marriage. Otherwise sex is ugly, and shameful. A very simple example is polygamy. That involves consensual sex, but for every man with ten wives, nine men must go wifeless. What are these men supposed to do – give up on life? Of course not. Daly and Wilson write in their book Homocide, the study of murder from an evolutionary perspective, that “Any creature that is recognizably on track towards complete reproductive failure must somehow expend effort, often at risk of death, to try to improve its present life trajectory.” One way these males can improve their life trajectory is by taking their rage out on their own society. An even better method is to take it out on a neighboring society. The old distinction between those who are “Like Us” and “The Other.” Either these unmarried young men will distinguish themselves in war, in which case they will be able to take wife (perhaps from among the vanquished tribe), or they will die. Either way the problem is solved. The anthropologist Napoleon Chagnon showed that the single best predictor of reproductive success among the Yanomamo is whether or not they had killed a man in battle.

This is a pretty typical finding in evolutionary biology. During mating season the males and females gather around a mating ground called a lek. The males fight to establish a territory on the lek. The females choose the males who establish the largest, most centrally located territory on the lek. The alpha males will acquire a large harem of females. The beta males - the vast majority of males - will have very little sexual access to females.

Let's not be guilty of assuming that polygamy is just an animal thing. There are three classic signs of a polygamous species and humans show all three. They are (1) Males are larger than females. That is because males are put into an arms race with other males to gain alpha status. (2) males are more aggressive than females. Don't think that this is "socially constructed". The anthopologist Donald Brown has found that male aggression is a human universal - it is found in every known human society regardless of how primitive. (3) Males delay adolescence compared to females. That gives males extra time to mature before becoming a sexual threat to older and stronger males. G.P. Murdoch has found that 80% of human cultures were at least partially polygamous prior to contact with the West.


Sperm are Cheaper than Eggs

The root cause of polygamy follows from a principle that I'm sure is familiar to any atheist who has ever read a popular book on evolution by someone other than Steven Jay Gould: sperm are cheaper than eggs. More generally, there is a large asymmetry in the amount of parental investment made by males compared to females. This forces females to be choosy and lets males be promiscuous. The outcome is polygamy as females choose an alpha male.

I see a few problems with this situation. The first is that it is inegalitarian. As a conservative I am sometimes asked by progressive why I don't care about inequalities in wealth (not to be confused with poverty). The answer is simple. The economy is not a zero-sum game. The fact that Bill Gates has 60 billion dollars also means that I am a bit richer myself. But the fact that an alpha male has ten wives does not mean that other males have two wives. reproduction is a zero sum game. Even if we disagree about whether or not there should be laws against polygamy, surely it is clear that a situation in which alpha males rule the roost is bad?

From an evolutionary perspective males in a species that is at least partially monogamous have two strategies. The first strategy is to develop a signal of genetic quality. That typically means highly developed secondary sexual traits like big muscles (if you are a human) or a large tail (if you are a peacock or a barn swallow).* The problem with the signal strategy is that it is essentially a waste. It is an arms race, a zero-sum game. Females are only concerned about the relative strengths of the signals. Suppose Adam has bigger muscles than Bob and neither works out. Then Bob goes to the gym, works out and takes supplements (possibly illegal supplements ...) and gets bigger muscles. Then Bob has improved his reproductive success but only be demoting Adam. Then Adam goes to the gym and passes Bob. Now Adam gets all the girls. So Bob works out two hours day. Then Adam works out two hours a day ...

Critics might object "well, if Adam and Bob want to spend all their free time in the gym that is their business." Fair enough, but time spent developing a signal of genetic quality takes away from the other path that males in a monogamous species can take: investment into their wife and children. In the case of barn swallows males can either develop a long tail (signal of genetic quality much like peacocks) or build a large nest. They both work as methods to attract a mate. But building a large nest is participating in a non-zero sum game. Large comfortable nests are better than small, ghetto nests. Males who compete in this domain end out making the world a better place, particularly for their children. They also help their wives and make life easier for them.


Monogamy

Lifelong monogamy is an act of love. That's because it solves the root cause of the "sperm are cheaper than eggs" dilemma. Monogamy forces males and females to make basically identical investments into their offspring. Conversely, once the link between sex and marriage has been broken, "sperm are cheaper than eggs" reasserts itself. The alpha males dominate.

* there are other signals besides big muscles. Intelligence, particularly in left-brained activities, probably plays a role. But it is clear that the evolutionary psyche motto of "stone age brain in a modern skull" has a large degree of truth, and thus promiscuity distorts male reproductive strategies in an unhealthy manner.