Although there has never been any considerable evidence for the first of these charges, it has frequently been repeated. Professor Montegazza of the University of Pavia collected data in regard to 512 cases of consanguineous marriage of which between 8 and 9 per cent were sterile, and with this basis he asserts that sterility is the only fact which can safely be deduced from his cases, since it cannot be hereditary.[43] But if in the nature of things absolute sterility is not inheritable, comparative infertility may be. And even then 8 or 9 per cent does not seem to be an excessively high proportion of sterility, especially if late marriages be counted. Boudin bases his assertion on this point on even less tenable grounds.[44] On the other hand some writers assure us that cousin marriages are even more prolific and less liable to sterility than the average.
[Footnote 43: See Darwin, "Marriages between First Cousins in England and Their Effects," _Journal of Statistical Society_, June, 1875, p. 178.]
[Footnote 44: Boudin, "Croisement des familles, de races et des espèces." In _Memoires de la Société d' Anthropologie_, vol. i, p. 518.]
The most important statistical investigation was made by G.H. Darwin.[45] From his genealogical data he compiled the following table:
TABLE XVI. ------------------------------------------------------------------------ | | Average | |Ave. no. | | number | Per cent |sons to |Number of | sons to | sterile |fertile |marriages.| marriage. | marriages. |marriage. ------------------------------------------------------------------------ Not consanguineous | 217 | 1.91 | 15.9 | 2.26 Parents 1st cousins[A] |97 to 105 |2.07 to 1.92|14.7 to 20.9| 2.43 One parent offspring of | | | | 1st cousin marriages. | 93 | 1.93 | 17.2 | 2.34 ------------------------------------------------------------------------ [A] Eight cases of doubtful fertility.
It will readily be seen that the conclusion is negative, since the variation is slight, but the higher fertility of the cousin marriages is interesting.
On the other hand de Lapouge quotes a case of a community founded two centuries ago by four families and populated almost entirely by their descendants, in which from 1862 to 1886 there were 273 marriages of which 63 were consanguineous and 26 were between first cousins. Among the non-consanguineous 3 per cent were uniparous, as against 7.95 per cent among the consanguineous. 7.5 per cent of the non-consanguineous were sterile as against 16 per cent of the consanguineous.[46] The importance of these percentages is impaired by the fact that they involve only five uniparous families and ten sterile ones, and that of these latter only five were sprung from first cousins.