Earlier today I commented on the hypothetical "Green Beard Effect" that may lead organisms to behave favorably toward other organisms displaying the same trait or traits.
The "Hey, we’re the same" instinct–whether it specifically captures what Dawkins et al. have in mind with the Green Beard Effect–is definitely something present in higher species (and many lower ones as well).
But there’s also the contrary impulse–what we might call the "Vive la difference" instinct–which causes us to favorably regard others specifically because their traits are different than ours.
Perhaps the most obvious example of this is the fact that we find the opposite sex attractive. If we didn’t, mating and reproduction wouldn’t occur and the species would die out. We are therefore genetically programmed to find those with the opposite sexual characteristics to be sexually attractive.
This instinct manifests in other ways, too.
For example, all human societies have an incest taboo. The nature of the taboo (i.e., exactly who you can’t marry) varies from culture to culture, but there is always an incest taboo of some kind. It is a human universal and thus seems to be based in our genetics.
The reasons for the incest taboo are debated.
One of the most common explanations you hear for why the incest taboo exists is that, if it didn’t and if a lot of incest went on as a result, it would harm the population by causing children to have birth defects due to inbreeding.
Maybe.
If that’s the reason for the taboo then it isn’t a conscious one. The ancients, who didn’t have access to modern science, didn’t seem to justify the prohibition of incest on those grounds.
St. Thomas Aquinas, for example, says nothing about it in his discussion of why incest is wrong.
I did some research a number of years ago on the subject (as part of answering the regular question "Where did Cain get his wife?") and found individuals arguing that the birth defects resulting from incest are not as common as is commonly supposed and that, if really severe, survival-affecting ones appear in a population, they’ll die out (or cause the population as a whole to die out). Also, until very recently, many humans lived in small, fairly isolated communities and didn’t have a lot of opportunity for marrying outside their neighbors, with the result that there has been a lot more inbreeding (if not incest) in human history than is often supposed.
Then there are people who argue the opposite of all this.
I don’t know which side is correct, but I mention the former position just to call attention to its existence, for you seldom hear it articulated.
My own suspicion is that we have the incest taboo because it’s just in us genetically and we have historically and are presently trying to come up with intellectual justifications for why something that we instinctively feel to be wrong is actually wrong.
In other words, it’s just part of the law of God written on the hearts of men.
God’s laws are for our good, and so I’m sure that there is a benefit–or several benefits–that come to mankind as a result of the incest taboo. One of them may be that it helps to prevent birth defects, but I’m not sure that there aren’t other, greater reasons.
In general, the incest taboo has the effect of bringing new genes into a family line and thus increasing its genetic diversity. Genetic diversity will allow it to withstand hardships better since there is a greater likelihood that some in it will be able to better weather the latest plague, famine, forced migration, or what have you.
A prohibition on inbreeding also helps broaden social ties, which result in an individual having greater social resources to draw upon. Of all the arguments that St. Thomas makes against incest, the one that strikes me as having the most force is this:
[Incest] would hinder a man from having many friends: since through a man taking a stranger to wife, all his wife’s relations are united to him by a special kind of friendship, as though they were of the same blood as himself. Wherefore Augustine says (De Civ. Dei xv, 16): "The demands of charity are most perfectly satisfied by men uniting together in the bonds that the various ties of friendship require, so that they may live together in a useful and becoming amity; nor should one man have many relationships in one, but each should have one."
If people marry outside their own families then the social fabric is strengthened and the society does better as a result.
Whatever the benefits God intends us to have as a result of the incest taboo–whether it’s avoidance of birth defects, increase of genetic diversity, stronger social ties, or a combination of these or something else entirely–we do have an aversion to incest that appears in all societies and that is likely genetic.
It would thus seem to involve a preference (at least in terms of mating) for those who are different from us in that they aren’t too closely related.
But the preferential option of those who are different goes beyond a preference for the opposite sex and beyond a preference for those who aren’t too closely related to us. There is some, though weaker, evidence that there is at least something of a drive in us toward exogamy, or marriage outside our own group.
The fact that most people marry within their own group and have done so historically suggests that this is a weak desire, but there is still an attraction to the exotic. People from other cultures can seem mysterious and romantic or their accents may be perceived as sexy.
Or not.
Like I said, it’s a weak desire in humans or people would have gone further afield to find mates than they historically did most of the time.
Nevertheless, we’re attracted not only by similarities but also by differences.
