Post a Comment On: Vigilance

I got another email the other day from a guy who wanted to challenge my beliefs. He wrote:
I know you hold Darwinist religious beliefs. Since you seem to think the desire to do certain stuff is a trait you're born with and since those who do that stuff don't tend to reproduce, doesn't your whole theory contradict the doctrine of natural selection. What I mean is, how is this trait passed on? Or is that desire just a very common mutation? Or maybe all those experts in those associations never considered that.
Ignoring the silliness about "Darwinist religious beliefs," let me say, I'm no evolutionary biologist, but I guess I have a thought or two on the subject.

Let's say, Darwinism can be looked at on at least two levels. At the level of the population, evolution is a change in the probability distribution of a phenotypic trait over time; change is usually seen as adaptation, though drift is possible, too, that is, random changes that do not affect fitness.

Evolution can also be looked at on the microscopic level. When we speak of genes for a trait, we mean patterns of DNA on the chromosome which function as a kind of developmental program for manifesting the traits biologically, almost always in conjunction with some environmental stimuli. Here we see evolution as change in the genotype, and it is possible that various genotypes produce similar phenotypes. For instance, human adaptations have arisen in both the Andes and in Kenya that allow individuals to run for a long time at high altitudes -- same phenotype -- but the genetic mechanisms are entirely different.

The PFOX types like to say "There is no gay gene." This is wrong in so many ways, it is hard to know where to start. First of all, there is no single gene for most complex traits. There is no introversion gene, no sense-of-humor gene, no musical gene ... Most human traits are supported by many, many locations on the chromosome interacting with one another, and interacting with the environment both in the deveopmental expression of the phenotype and in predisposing a response in the moment.

As I've reported here before, patterns on the chromosome have been found, which correlate with homosexuality. Patterns in the brain have been found, too, which are probably a function of development rather than learning. But to find a "gay gene," we would need to see a pattern that every gay person has, and no straight person, and that just ain't gonna happen. You will find parts of patterns here and there, and various combinations of those patterns which, combined with some environmental factors -- which can be hormones in the womb or childhood experiences or anything else, nobody knows for sure -- result in the person preferring partners of their same sex.

You see this nullifies the argument that it can't be inherited. Parts of patterns can be received from one parent and parts from the other, with neither parent having the entire combination of alleles that would make them gay (and we would really expect different patterns to work for males and females, meaning for instance that a female could carry the whole set of gay-male genes, with no effect). If there are many patterns with a similar effect -- and redundancy is an important feature of genetics -- then this becomes even more likely.

There's another thing, which is hard to grasp. As I mentioned, evolution can be seen to work at the level of the species or population. It is very common to find adaptations that are bad for the individual and good for the group. Just think of a male bird's bright colors, which serve the function of attracting mates, and also of attracting the attention of predators in order to lure them away from the nest. There is risk in that, and in fact some male birds are killed performing this stunt, but overall it is adaptive for the species.

I note that some persons seem to believe they have inside knowledge about what is "natural," or what God intended when He created certain things, but I tend to believe that God's true intent is mysterious, and that it is usually foolish to try to reason about how a trait increases the fitness of a species.

There is nothing contradictory about homosexuality being inherited.