SEX-RATIO AND SELECTION BY EARLY MORTALITY IN HUMANS - 50-YEAR ANALYSIS IN DIFFERENT ETHNIC-GROUPS

We studied the sex ratio (M/F) in representative populations of the ma in human ethnic groups, namely, US whites, US blacks, and Japanese. Th e data cover a period of over 50 years. For intra-ethnic comparison, w e included analogous data on Italians. The populations studied show he terogeneous patterns: the US white and Italian populations are the mos t similar, with no drastic variations in live-birth sex ratio througho ut the period. Comparison of sex ratio data for live-borns and 1-year- old infants yields a similar pattern in all groups; the differences be tween the two sex ratio values are constantly reducing. It can be hypo thesized that in the near future the sex ratio observed at birth will be maintained up to reproductive age. If this value is stabilized by n atural selection, as is likely, new relationships between the sex rati o and selection are expected to evolve in the populations of developed countries.