[Sidenote: The custom of avoiding relations by marriage cannot be separated from the similar custom of avoiding relations by blood; both are probably precautions to prevent improper relations between the sexes.] It would be easy to multiply examples of similar customs of avoidance between persons closely connected by marriage, but the foregoing may serve as specimens. Now in order to determine the meaning of such customs it is very important to observe that similar customs of avoidance are practised in some tribes not merely between persons connected with each other by marriage, but also between the nearest blood relations of different sexes, namely, between parents and children and between brothers and sisters;[84.2] and the customs are so alike that it seems difficult or impossible to separate them and to offer one explanation of the avoidance of connexions by marriage and another different explanation of the avoidance of blood relations. Yet this is what is done by some who attempt to explain the customs of avoidance; or rather they confine their attention wholly to connexions by marriage, or even to mothers-in-law alone, while they completely ignore blood relations, although in point of fact it is the avoidance of blood relations which seems to furnish the key to the problem of such avoidances in general. The true explanation of all such customs of avoidance appears to be, as I have already indicated, that they are precautions designed to remove the temptation to sexual intercourse between persons whose marriage union is for any reason repugnant to the moral sense of the community. This explanation, while it has been rejected by theorists at home, {85} has been adopted by some of the best observers of savage life, whose opinion is entitled to carry the greatest weight.[85.1]