Abstract
SummaryThe fitness of human zygotes depends on both biological and demographic parameters. Some of the demographic parameters are changing at present in this country and accurate estimates of them are not available but this imprecision has no great bearing on the estimate of fitness offered below.Of 100 human zygotes, now, in this country, it is estimated that embryonic and early fetal loss (before the end of the 3rd month) accounts for 44; induced abortion, 7; late fetal loss (after the 3rd month), 4; and mortality between birth and maturity, 1½. Of the remaining 43½ who reach maturity, it is estimated that 8 fail to reproduce, leaving 35½ who do reproduce.The standard error of this estimate must be large because of the large standard error of the estimate of the incidence of natural reproductive wastage from which it was derived.
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