Logic For Islamic Rules

Marriage Among Blood Relations

Question: Under what conditions marriage among two blood relations is not considered to have adverse effect on health?

Answer:[1] Nearly one century earlier Mendel had, after eight years research, discovered a principle of heredity which we explain below in simple language for the information of readers.

If two mice are mated, one white and the other ash colored, their offspring will unconditionally have ash color, while if the two of the same group are mated, some mice will have ash color and others white.  White and ash color has been mentioned as a characteristic. As stated above, the mice of the first generation will all have ash color, i.e. out of the two characteristics of the parents one will be reflected completely while the other will remain hidden.  In technical terms, the characteristic that emerges, i.e. ash color, is called dominant and the other, i.e. white, is referred as overcome.

In the example, the agent determining the color, ash or white, is called Genes which brings child into life through the reproductive cells of parents.

When the reproductive cells bringing an animal into life, i.e. Genes, have similar characteristics, it is called homogeneous.  It is an established rule that such a creature will create similar reproductive cells and the result of two similar persons

[1] This reply has been given by Dr. Faridun Zanganah.

 mating will be the birth of such children who will be exactly like their parents in relation to the characteristics under discussion.

When the reproductive cells bringing an animal into life, i.e. Genes, have dissimilar characteristics, that creature will be referred to as heterozygote.  In the above example, the ash color mice that were born in the first generation are referred as adulterated, as one type of Genes was ash color while the other was white.  There is no doubt that their reproductive cells were not similar; rather 50% Genes were producing ash color while the other 50% were having white Genes.  It is clear that due to mating of two adulterated pairs, the offspring are not born who would be having the same properties as those of their parents.  In the above example, some of the second generation mice will have white color while other will have ash color.

After this introduction that was given to the beloved readers to acquaint them with the fundamental rules of heredity, we now come briefly to the real issue, that is, the effect of marriage among two blood relations from the point of view of religion.

It has now been proved that if any family has hereditary disease, the marriage among its blood relations is not out of danger, as the child born of such family is more likely to suffer from the hereditary disease than in the case of the family not having blood relations. (This point is explained below in greater detail).

If two persons suffering from a dominant hereditary disease get married among their families, all their children will have dissimilar genes; in other words, they will be homozygote.  The childrens disease will be more severe than that of their parents.  The disease may even be so severe that in some cases the homozygote may die before or a little after birth.

If one of the parents does not have the genes carrying such dominant hereditary disease then all the children will not suffer from it, and those who do suffer, their disease would not be severer than that of their parents.

In the case of the overcome disease, if the father or mother is heterozygote, then one fourth children will suffer from the hereditary disease, while if one of the parents does not have the genes of the disease, then no child will suffer from the disease.  However, in the second case, half the children will be heterozygote, but due to the disease being overcome, it will not appear in the heterozygote.

Keeping the above facts in view, people are advised to avoid marrying among their blood relations as far as possible.

However, it should be remembered that if husband and wife are not suffering from any hereditary disease, then there is no harm in such marriage.  Therefore, for persons to feel that

 marriage among blood relations is always harmful is totally baseless.  Rather such marriage is harmful if a hereditary disease is there.  What can be said for sure is that in doubtful cases, it is better to be careful and to avoid such marriage.  Perhaps that is the reason why in some traditions it has been advised that marriage of boys and girls among cousins should be avoided, except in exceptional cases, and to avoid it has been considered better.