Why do men cheat?

In the wake of the Tiger Woods scandal, USA Today asks why men cheat. Personally, I think it’s the wrong question. Biologically, men are sperm production machines. We release roughly 40 million of the little buggers every time we ejaculate. This fact simultaneously contributes to, and is a result of, a strategy for increasing the number of human beings in the world. This strategy has been exercised by men and women for tens of thousands of years. Some of the elements of this strategy:

1. The fact that women have ridiculously small production of eggs compared to men’s production of sperm, means that women are in general, more selective about their sexual partners. They want both:
   

   1. Men who will commit a lifetime to them in order to help provide stable child care
      
   2. Men with the strongest genetic material, to increase the odds of survival of their children
      

   This often results in a problem for women, because of this statistical fact: not all women can have above average lifetime mates. By definition, not all men are above average. There’s no getting around the fact that, on average, men are average. So, on average, women find themselves choosing either a or b, but not both.
   
   
2. On the other hand, men’s production of ridiculously large numbers of sperm means that sperm are in plentiful supply. To replace the current generation, any given society needs to have all (or nearly all) of the women reproduce. But only a very small number of men are needed to accomplish the same thing. The rest of the men are expendable. Hence, they are available to take on the much more risky tasks, like protecting the group from invaders, getting meat, etc.
   

The results of the extremely high costs of female eggs and the extremely low costs of male sperm is the strategy that got us to where we are today: relatively small number of men have historically reproduced. The remaining men simply died off. Those who did reproduce, had to be among the horniest buggers of all time. Those who weren’t that horny simply died off.

So what are men now? We’re the descendents of long lines of the horniest and most reproductive men ever. This tiny minority of men had sex with almost all the women. The women wanted this because they all had access to the best genes which meant a higher probability that their children would survive. The men wanted this because it let them spread their genes most widely. The offshoot? Men are horny buggers because we’re descended from horny buggers. And women enabled this trait by giving birth to offspring from that tiny minority of men.

And this is borne out by studies of genetic lineage. Some studies of China have found that 8% of that population is a descendant of Genghis Khan (1). Think about that. One out of every 12 people, in a society of over 1 billion, are descended from one man. Other studies have found that, historically, only 40% of males reproduced. The remaining 60% died before having children (2).

The long and short: all of us (in general) but specifically men have an incredible biological urge to promiscuity, because we are descended from long lines of men who successfully deployed this strategy, and we inherited the desire to do the same.

So the question is *not* why do men cheat. The question is why don’t they.

And the answer is, I think, related to how marriage benefits the 60% of men who previously didn’t get to reproduce. Without the institution of marriage, almost all women would reproduce. But only 40% of men would. Marriage, and the social pressure to remain faithful, provides benefits for both men and women. For most women it provides them a long term caretaker. For men, it provides that other 60% the ability to reproduce. An ability that they simply didn’t have before.

Marriage is, I think, an emergent social norm that maximizes reproduction for both men and women. It’s a good thing. *BUT* don’t forget our biological history. It’s that history of success that makes it so hard for men to not cheat. Men find themselves trying to walk a tightrope. They have enormous biological pressure pushing them towards infidelity, and social pressure pushing them towards faithfulness. It should be little surprise that several slip off that rope.

UPDATE: I just realized something. A) I am a lifetime companion to my wife. B) I've never been approached or seduced by any woman, ever. I therefore have to conclude that, apart from marraige, I'd have fallen into the 60% of men who never got to reproduce. This conclusion is corroborated by my experience in high school, and the observations of a former boss. After work at the bar, he told me I had "no game" - meaning that I couldn't pick up a woman if I really wanted to. I objected saying that I got married and was able to pick up at least one woman. His response: that was just pity. Over the years, I've come to realize he was right. My point: there's at least one positive about being in the bottom 60%.

Cited References:

1. http://news.nationalgeographic.com/news/2003/02/0214_030214_genghis.html
   
2. http://www.psy.fsu.edu/~baumeistertice/goodaboutmen.htm FYI, this article is worth reading in its entirety.
   

Additional references:

1. http://jessiegirl.blogspot.com/2008/11/monogamy-part-1-impossible-dream.html
   
2. http://opinionator.blogs.nytimes.com/2008/09/16/a-commitment-pill/?apage=3