It is at the outset clear that savages are not in the habit of taking account of such matters.  Even if it were otherwise, it is not clear how far they would have data as to the varying results of unions of near kin.  For though on this question, so far as the genus homo is concerned, we have very few data on which to go, such data as we have hardly bear out his view.  Modern statistics relate almost exclusively to the intermarriage of cousins, and apply, not to primitive tribes, such as those with which, ex hypothesi, Mr Morgan is dealing, but to more or less civilised and sophisticated peoples, among whom the struggle for existence is less keen owing to the advance of knowledge and the progress of invention, and among whom possibly the rise of humanitarian ideas not only tends to counteract the weeding out of the unfit, but even makes it relatively easy for them to propagate their species.  What the result of the intermarriage of cousins is when war, famine, and infanticide are efficient weeders out of the unfit, we cannot say.  Possibly or even probably the ill results would be inappreciable.  It must not be forgotten that the marriage of near relatives is only harmful because or if it hands on to the children of the union an hereditary taint in a strengthened form, a result which is likely to follow in civilised life because hereditary taints are allowed to flourish unchecked by prudence and controlled by natural selection only so far as humanitarianism will permit it.  These hereditary degeneracies however are probably largely if not entirely absent among savages.  It is therefore open to question how far intermarriage of cousins would prove harmful under such conditions.

Statistics of the influence of cousin-marriage are not however what Mr Morgan wants.  It is essential for him to prove that father-daughter marriage is more harmful than brother-sister unions.

It might be imagined that the data for estimating the effect of the union of father and daughter would be non-existent, but this is not so.  Within the last few years it has been stated that such unions are common in parts of South America, and that the children, so far from being degenerates, are remarkably healthy and vigorous[149].  This is of interest in connection with Mr Atkinson’s speculations as to the history of the family.  In this connection it may be pointed out that such unions, ex hypothesi, are unlikely to result in continual in-and-in breeding, and would in all probability seldom be continued beyond the first alliance of this nature.

We are practically in complete darkness as to the results of brother and sister marriage in the human species.  We have of course various cases of ruling families who perpetuated themselves in this way, but the data from such peoples refer to an advanced stage of culture and to a favoured class.  They are not therefore applicable to similar unions among savages where they formed, as Mr Morgan suggests, the invariable