The natural history of population : University of London Heath Clark Lectures 1937 delivered at the London School of Hygiene and Tropical Medicine / by Raymond Pearl.

  • Raymond Pearl
Date:
1939
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Licence: In copyright

Credit: The natural history of population : University of London Heath Clark Lectures 1937 delivered at the London School of Hygiene and Tropical Medicine / by Raymond Pearl. Source: Wellcome Collection.

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    probable that Fig. 4 does represent a fair approximation to the general average situation. It cannot of course be regarded as applying to particular individual subjects. 4. Innate Reproductive Capacity It admits of no reasonable doubt that there are marked differences between individual human beings in respect of their innate reproductive capacity, though for obvious reasons these are extremely difficult to measure precisely. Fig. 4. Rhythm of sex desire (heavy line) and frequency of conception from timed single coitus (light line). [From Tinklepaugh, based on Dickin¬ son’s data.] In man too many other disturbing factors influencing the overt expression of fertility come into the picture, and, as has already been pointed out, fecundity cannot be directly measured in man. But in various lower organisms, where fecundity can be measured, it has been shown that there are great individual differences and that these are inherited. Thus, to take a single example, Pearl and Surface (09) showed that in a homogeneous strain of the domestic fowl the number of eggs laid in a year ranged in different in¬ dividual birds from 1 to 248 inclusive. It was further shown (Pearl and Surface, 10; Pearl, 12) by experiments in crossing a breed of relatively high innate fecundity (Barred Plymouth Rock) with one of relatively low fecundity (Cornish Indian Game) that fecundity was inherited in a manner accordant with a simple Mendelian hypothesis. A number of direct ad hoc attempts have been made to measure biometrically the degree of inheritance of human fertility, by the technique of correlating size of completed