establish a connection between food
conditions and the determination of sex. But behind the mere fact that a
different attitude toward food determines difference of sex lies the
more fundamental--indeed, the real--explanation of the fact, and this
chemists and physiologists are not at present able to give us.
Researches must be carried farther on the effect of temperature, light,
and water on variation, before we may hope to reach a positive
conclusion. We can only assume that the chemical constitution of the
organism at a given moment conditions the sex of the offspring, and is
itself conditioned by various factors--light, heat, water, electricity,
etc.--and that food is one of these variables.[15] It is sufficient for our
present purpose that sex is a constitutional matter, indirectly dependent
upon food conditions; that the female is the result of a surplus of
nutrition; and that the relation reported among the lower forms persists
in the human species.
In close connection with the foregoing we have the fact, reported by
Maupas,[16] that certain Infusorians are capable of reproducing
asexually for a number of generations, but that, unless the individuals
are sexually fertilized by crossing with unrelated forms of the same
species, they finally exhibit all the signs of senile degeneration, ending
in death.[17] After sexual conjugation there was an access of vitality,
and the asexual reproduction proceeded as before. "The evident result
of these long and fatiguing experiments is that among the ciliates the
life of the species is decomposed into evolutional cycles, each one
having for its point of departure an individual regenerated and
rejuvenated by sexual copulation."[18]
The results obtained by Maupas receive striking confirmation in the
universal experience of stock-breeders, that, in order to keep a breed in
health, it is necessary to cross it occasionally with a distinct but allied
variety. It appears, then, that a mixture of blood has a favorable effect
on the metabolism of the organism, comparable to that of abundant
nutrition, and that innutrition and in-and-in breeding are alike
prejudicial.
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
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