Westermarck and Incest Laws

I have written a number of posts on Edward Westermarck's Darwinian theory of the incest taboo, one of which can be found here.

Westermarck's theory illuminates some of the reasoning for Darwinian natural right. First of all, it provides one of the best illustrations of a Darwinian account of morality as arising from a complex interaction of genetic propensities, cultural traditions, and individual judgments. More specifically, it's an example of how this reasoning can be applied to the study of law.

Last week, I led my students in my philosophy of law class in a discussion of an article in the Harvard Law Review on incest laws in the United States. Although the author of this anonymous Note shows no knowledge of Westermarck's theory, one can see how the article's analysis would have been deepened by some application of Westermarck's theory.

The Note shows the great diversity--and even confusion--in the incest laws of the United States as they vary across states. The author proposes a new standard that would create consistency in the laws. The new standard would be based on a distinction between consensual and nonconsensual incest. Where individuals are in a "natural dependency" relationship of caretaker and dependent--as in mother and child--sex would be prohibited. But "consenting adults" would be free to engage in sexual relationships with one another. The underlying principle is John Stuart Mill's principle of individual liberty. Although this standard is unlikely to be enacted in law, it does point to the need for clarification of our incest laws.

To illustrate some of the confusion in the law, consider some of the cases covered in the article. Rhode Island law permits Jewish marriages between uncles and nieces. In In re May's Estate (1953), a New York court had to decide whether an uncle and niece married in Rhode Island had a valid marriage in New York. The court upheld the marriage, because it "was not offensive to the public sense of morality to a degree regarded generally with abhorrence and thus was not within the inhibitions of natural law." The author of the Note agrees with the outcome of this case but dismisses the appeal to "natural law" as purely "subjective" judgment.

In the case of Israel v. Allen (1978), the Colorado Supreme Court struck down as unconstitutional a statute that prohibited marriage between siblings related by adoption. The parents of the married couple in question had married when the children were teenagers. The court argued that biologically unrelated people are less likely to produce children with genetic defects due to inbreeding. Consequently, the marriage of adoptive siblings doesn't produce the same "natural repugnance" or "moral condemnation" as a marriage of people who are biologically related. Moreover, in this particular case, there was no evidence that the adoptive siblings had ever lived together in the same household. Again, the author of the Note accepts the outcome of this case but scorns the reasoning in the decision. The court's reasoning is said to be confused because it tries to establish some standard of what counts as an acceptable family, but in this case these adoptive siblings both are and are not members of the same family.

Applying Westermarck's theory would help us to understand what is going on here. When children are reared in the same family from an early age, they are naturally inclined to feel a sexual aversion towards those with whom they have been reared. This propensity to learn such an aversion is probably the consequence of an evolutionary history to favor behavior that is less likely to result in inbreeding that reduces fitness. This is largely an unconscious psychological process. But it can also be reinforced by conscious reasoning insofar as societies become aware of the problems of inbreeding.

We can predict that our moral repugnance will be strongest towards incest within the nuclear family, which explains why all states in the United States prohibit the marriage of full-siblings and between parents and children. But we typically feel less abhorrence towards the marriage of step-relatives who have not grown up together. And we disagree in our reactions towards cousin marriages. Many states permit cousin marriages, but the majority prohibit cousin marriages. The psychology of the Westermarck effect allows us to explain what would otherwise seem to be utter confusion in the laws of incest.

How exactly we should write our laws on incest is a matter of customary traditions and deliberate choices. Our formal laws might move in the direction suggested by the author of the Note, which would give "consenting adults" a lot of freedom in deciding whom they want to marry. But we could still enforce customary social norms through social pressure even without legal coercion.

As I have indicated in a previous post on the "good eugenics" practiced by American Jews, some Ashkenazi Jews have procedures for testing children to see if they are carriers of Tay-Sachs and other genetic maladies, and then they use voluntary means to encourage their children to consider the potential risks in their choice of marital partners.

We should use legal coercion only to enforce those norms that we can all agree on as expressing our deepest moral sense about clear harms that we want to avoid. But we can also enforce the moral norms of civil society through social persuasion without formal legal coercion.