Evolution, Homosexuality and Birth Control

Several years ago my brother and I were talking about evolution.  My brother expressed the opinion that people sometimes used natural selection to explain too many things.  There were some features of life that it could not.  I asked for an example.  My brother gave homosexuality and drug addiction as examples.

I think this illustrates a point.  Explanations are required to explain order, rather than disorder.  We need no scientific theory to explain why the arrangement of stars in the sky is more or less random.  We can come up with explanations for why there is homosexuality and drug addiction because of natural selection, but this generally involves explaining that certain traits that humans have, which were caused by natural selection, lead in some cases to drug addiction and homosexuality, which do not tend to aid survival and reproduction.

First I will take homosexuality.  This is part of a wider phenomenon, sexual orientation.  It would be possible for humans to live without sexual orientation.  That would involve all humans being bisexual and indifferent to gender when it came to selecting a sex partner.  That would be a state of disorder.  I am not saying that we should disapprove of such a state for any individual.  What I am pointing out is that this would be less of a pattern than what we see.

Now we can easily argue that sexual orientation generally helps human individuals survive and reproduce.  The vast majority of people are heterosexual, and this tendency is present in a wide variety of cultural settings.

The fact that some individuals are not heterosexual doesn't undermine the explanation that natural selection explains sexual orientation.  We have a mechanism that tends to cause people to form sexual bonds that lead to reproduction.  Total and complete order in this regard would be everyone having the same preference, either 100% being homosexual or 100% heterosexual, or every member of the population preferring the same gender.  That some people have a preference that doesn't fit the pattern means that we have something short of this.

However, we cannot say that we have complete and total disorder either.  Given that we have sexual orientation, which is a form of order, the most disorder we could have is for sexual orientation to be a random assortment.  There would be just as much homosexuality as heterosexuality.  This is not the case.

Now with drug addiction the explanation is that there is some chemical signal for pleasure.  Pleasure serves the purpose of motivating individuals to act in ways that lead to survival and reproduction.  The brain uses signals to send messages from one part of the brain to other parts.  Signals must be either chemical or electrical.  I suspect that there are some reasons why using chemical signals in some instances might be preferable to using electrical ones.  So long as the brain uses chemical signals to encourage certain behaviors, there will always be a way for individuals to obtain pleasures by consuming either the chemicals that are used to give the appropriate signals, or ones that mimic the actions of those chemicals.

Thus in both of these instances there is an explanation that uses natural selection even though neither of these behaviors is adaptive.