[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 especes.”  In Memoires de la Societe 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.
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------------
|          |  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.

[Footnote 45:  Op. cit., p. 181.]

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.

[Footnote 46:  De Lapouge, Les Selections Societies, p. 196.]

It is almost impossible to get any accurate statistics of sterility from genealogies, for when no children are given in the record, there is always a strong possibility that there were children of whom the genealogist has no record.  However, of 16 first-cousin marriages of which the record expressly stated “no issue,” or where it was practically certain that no issue was possible, the average age of the brides was 34.3 years and that of the grooms was 39 years, showing that consanguinity could not have been the only cause of their sterility.

In regard to relative fertility the figures are reliable, but they fail to indicate any effect of consanguinity upon fertility, as will be noted in Table XVII.