Ken Ham and his associates regard the Mosaic commandment against incest as a contingency brought about as a response by God to genetic degeneration (pp. 24-29). The idea is that harmful genetic mutations brought about by the curse resulting from Adam’s Fall are more likely to propagate to the next generation when father and mother are closely related, because the bad genes are more likely to “line up” and produce a gene pair in which both genes are defective, thus inflicting that disadvantage in the feature controlled by that gene pair in the offspring, while parents that are more distantly related are likely to have genetic defects that don’t line up, so that each gene pair is likely to have at least one gene that is not mutated.
By the time of Moses (about 2,500 years later), degenerative mistakes would have accumulated to such an extent in the human race that it would have been necessary for God to bring in the laws forbidding brother-sister (and close relative) marriage (Lev. 18-20). Also, there were plenty of people on the earth by now, so close relations did not have to marry. (p. 29)
The view here presented is the opposite of the traditional theological viewpoint represented for example by Dabney, who taught that the incest prohibition is part of the Moral Law, and that the first-generation coupling of siblings was an exception (Lectures in Systematic Theology, pp. 412f.). He takes note of the same genetic degeneration as Ham, but places it in the opposite causal relation to the law:
Man’s animal nature now utters its protest, by the deterioration and congenital infirmities, which it visits usually on the unfortunate children of these marriages within lawful degrees. (p. 413)
Apart from the modern insight into genetics, it is hard to see how natural reason would lead to the prohibition. Yet we find the incest taboo universally acknowledged, even in the most depraved of societies. It seems to be etched on the conscience of man even though, of all the “Moral Law,” the least susceptible to rational explanation. The Moral Law has its force because it is graven on the mind of man by direct divine revelation or implantation, so that man in his rebellious state, though he cannot obey it, finds himself accusing and excusing in terms of it (Rom 2:15).
For this reason, the caution flags should go up for Ham’s new theory. If Ham’s theory is correct, then the incest prohibition is not part of the eternal Moral Law, but is contingent on the fact of genetic mutation. At most, we could say that it is a circumstantial application of the Moral Law thou shalt not slay in its positive application of the preservation of life as applied in love for the next generation. If that is the case, then we could say that this law would be fulfilled even in the apparent breach, if the circumstance that defines it – genetic mutation – could be vouchsafed not to apply in a particular case.
Suppose, for example, that the science of genetics reached such a level of sophistication, that a brother and sister could submit genetic samples, and laboratory analysis could determine that none of their “bad genes” in their case would ever line up. Could they then marry, on the ground that the whole purpose of the incest prohibition, being circumstantial, did not apply in their circumstance?
I am inclined to think that this line of thought cannot be sustained.
1. The biblical prohibitions of consanguity include in-law marriage, such that the genetic argument would fail. This principle is summarized in the (original) Westminster Confession this way:
24.4 Marriage ought not to be within the degrees of consanguinity or affinity forbidden by the Word; nor can such incestuous marriages ever be made lawful by any law of man or consent of parties, so as those persons may live together as man and wife. The man may not marry any of his wife’s kindred nearer in blood than he may of his own; nor the woman of her husband’s kindred nearer in blood than of her own. (emphasis added)
The American revision (used, for example, by the OPC) deletes that last sentence. However, it is hard to see how the original version can be avoided, because of this text:
Leviticus 20:19-21 And thou shalt not uncover the nakedness of thy mother’s sister, nor of thy father’s sister: for he uncovereth his near kin: they shall bear their iniquity. And if a man shall lie with his uncle’s wife, he hath uncovered his uncle’s nakedness: they shall bear their sin; they shall die childless. And if a man shall take his brother’s wife, it is an unclean thing: he hath uncovered his brother’s nakedness; they shall be childless.
This is a big topic, and I don’t want to pretend to be able to give more than an amateurish “first word” on it. James Thornwell discusses the topic in connection with the McQueen case in his discussion of the General Assembly of 1847 (Works, vol. 4, pp. 488-494). Barry Waugh wrote his PhD dissertation discussing the issue at length, with a journal article summarizing the results. The topic is important and interesting, and we should take it up more thoroughly again in the future.
But in any case, it is clear that Moses at any rate could not have conceived of his giving the laws pertaining to incest from the motivation described by Ham, since the Mosaic law includes affinity by marriage, where the genetic argument would not have any force. It is interesting that just at this point, Moses emphasizes that the couple must be separated and thus remain childless – the very topic in which the genetic argument has force; yet here, that is clearly not in view.
2. If the brother/sister argument from genetics has some plausibility, would Ham extend the principle even to mother/son, father/daughter relations? There would be no prohibition apart from the problem of genetic mutation? It staggers the imagination.
3. A serious objection to Ham’s way of thinking here is the implied naturalistic perspective. It is as if God unleashes a tornado that he must now figure out how to respond to. He causes the principle of genetic mutation as a consequence of his own curse, but now that this cat is out of the bag, he must find a way to leash it in. Thus, God’s orientation to physical law is the same as ours: he, just like us, must respond to it, find ways around it. It would be “necessary for God to bring in the laws”; fortunately, He did not have to dance around one potential constraint, for “there were plenty of people on the earth by now, so close relations did not have to marry.”
The same mistake was made in the last generation, when it was often claimed that the prohibition of pork as unclean was God’s “response” to the higher disease-carrying proclivity of swine. It was actually a Methodist friend of mine that pointed out at the time that the exact opposite is far more likely the case: God having declared the pig unclean, he then afflicted it with disease in consequence thereof.
Some speculation is inescapable; but my Methodist friend’s is by far the more theologically sound speculation. The other one places God in a wrapper of darkness, in which he must probe and discover and respond. He creates a monster that he must now figure out how to tame. Far better to say that the pig’s design plan included certain characteristics that would intentionally ratify its function as a symbol of the unclean during that stage of redemptive history. Far better to say that genetic mutation was introduced as a punishment for violation of the incest prohibition: though we cannot deduce this as a church dogma.
Though the incest discussion is a minor one in the scope of Ham’s dissertation, it is telling nonetheless. A poisonous naturalism pervades all of his arguments, seen particularly clearly here. There is a covenantal way to account for genetic defects and swine parasites, and there is the naturalistic way. Overcoming the naturalistic perspective is the genius of a truly Christian exposition. Like a besetting sin, it must be re-overcome again and again.