Factors affecting the Human Sex Ratio

Son-biased sex ratios in the 2000 United States Census

“…Lower parity children were older, but were born to younger mothers, two factors known to exert small and roughly offsetting effects on the sex ratio. As for sex of previous children, there may have been a small tendency toward repeating the same sex (1,12).…”

Sources of variation of the cattle secondary sex ratio

“…Analyses of this factor in different data sets of humans and domestic species showed controversial results. For example, in human populations, Renkonen et al (1962) and Edwards (1966) and, in cattle, Astolfi (1990a,b) found a positive significant correlation between sexes in consecutive births, while Edwards and Fraccaro (1960) and Greenberg and White (1967) did not find any evidence of association. Gray and Hurt (1979), in cattle, and Gray and Katanbaf (1985), in swine, did not obtain statistically significant results, though correlations between sexes were generally positive.…”

“…These analyses, carried out using models which did not provide simultaneous controls for many effects, nevertheless indicated the importance of different kinds of variation (Gini, 1951;Edwards, 1958;Edwards and Fraccaro, 1960;Renkonen et al, 1962;Beilharz, 1963;Edwards, 1966;Greenberg and White, 1967;James, 1975 In a previous analysis (Astolfi, 1989) In the latter case, attention was focused on the sex of the first 4 calves, pooling longer sequences into the same class.…”

The Birth of Mongoloids

“…Regularities in the composition of the previous subship (7), differences in time intervals between the successive children (12,6) and the increasing sex ratios (in/f) among stillbirths with increasing birth order (5) m ay be ex plained on the basis of the m others' altered reactivity against her male fetuses. After the birth of few boys the reactivity of a fraction of the mothers seems to increase (13,6). Some of our argum ents and interpretations have been criticized by Edwards.…”