If this is true, and if heightened nutrition yields an increased proportion of females, we ought to find that breeding-out is favorable to the production of females, and breeding-in to the production of males; and a considerable body of evidence in favor of this assumption exists.[19]

Observations of above 4,000 cases show that, among horses, the more the parent animals differ in color, the more the female foals outnumber the male.  Similarly, in-and-in-bred cattle give an excessively large number of bull calves.  Liaisons produce an abnormally large proportion of females;[20] incestuous unions, of males.[21] Among the Jews, who frequently marry cousins, the percentage of male births is very high.

According to Mr. Jacobs’ comprehensive manuscript collection of Jewish statistics ... the average proportion of male and female Jewish births registered in various countries is 114.5 males to 100 females, whilst the average proportion among the non-Jewish population of the corresponding countries is 105.25 males to 100 females....  His collection includes details of 118 mixed marriages; of these 28 are sterile, and in the remainder there are 145 female children and 122 male—­that is, 118.82 females to 100 males.[22]

The testimony is also tolerably full that among metis and among exogamous peoples the female birth-rate is often excessively high.[23]

Viewed with reference to activity, the animal is an advance on the plant, from which it departs by morphological and physiological variations suited to a more energized form of life; and the female may be regarded as the animal norm from which the male departs by further morphological variations.  It is now well known that variations are more frequent and marked in males than in females.  Among the lower forms, in which activity is more directly determined mechanically by the stimuli of heat, light, and chemical attraction, and where in general the food and light are evenly distributed through the medium in which life exists, and where the limits of variation are consequently small, the constitutional nutritive tendency of the female manifests itself in size.  Among many Cephalopoda and Cirripedia, and among certain of the Articulata, the female is larger than the male.  Female spiders, bees, wasps, hornets, and butterflies are larger than the males, and the difference is noticeable even in the larval stage.  So considerable is the difference in size between the male and female cocoons of the silk-moth that in France they are separated by a particular mode of weighing.[24] The same superiority of the female is found among fishes and reptiles; and this relation, wherever it occurs, may be associated with a habit of life in which food conditions are simple and stimuli mandatory.  As we rise in the scale toward backboned and warm-blooded animals, the males become larger in size; and this reversal of relation, like the development of offensive and defensive weapons, is due to the superior variational tendency of the male, resulting in characters which persist in the species wherever they prove of life-saving advantage.[25]