Sex ratio of livebirths in Micronesia

Abstract

A growing body of data extends Hunt's earlier findings from Yap to suggest a characteristic Micronesian pattern of highly masculinized secondary sex ratios. Using materials from an extensive family record register for pre-World War II Guam, it is now possible to examine parental age and birth order effects in a Micronesian population in which the overall sex ratio of livebirths to 3,406 formally wed and fertile couples was 109.6. In contrast to the results of most studies among Euroamerican groups, secondary sex ratios on Guam were significantly higher for higher order births and for paternal age at last recorded birth to older couples. This apparent anomaly is resolved, however, and James' hypothesis of human sex ratio determination is supported when universalistic assumptions of declinin coital frequencies with spousal age and marital duration are replaced by more appropriate and population-specific ethnodemographic information. © 1995 Wiley-Liss, Inc.

They also serve: Chamorro male fertility in the pre-world war ii period

“…(Pool, 1991, Table 6.2) 6.9 Fiji 1950-55 (Ahlburg, 1996, Table 2) 6.6 Papua New Guinea 1950-55 (Ahlburg, 1996, Other standard fertility estimates which depend on the availability of census materials from which life tables can be constructed include the gross reproduction rate (GRR) and an approximation of the net reproduction rate, the replacement index (RI). Given characteristic Chamorro secondary sex ratio patterns for the period (Underwood, 1993(Underwood, , 1994(Underwood, , 1995, concerns about declines in sex ratio with parental age are not warranted in calculating GRR, an estimate of the number of offspring which would be born to parents of the same sex. The replacement index provides an approximate forecast of the number of same-sex offspring which would be produced by parents of either sex, assuming fixed fertility and mortality schedules.…”

Martin's treatment of the human sex ratio at birth

“…This statement is correct, but not all of these populations show a monotonie decline. Some (cited by Martin 1994a) show an increase, and the data of Underwood (1995) from Guam show a U-shaped regression of sex ratio on birth order. Lastly, Martin's (1994a) own data show no such regression since 1970 (apparently obliterated by increasing numbers of illegitimate, disproportionately female, births to young women).…”

“…I have never seen data suggesting anything but a monotonie decline in coital rate with duration of marriage. However, Underwood (1995) articulates a view apparently espoused by Martin. She writes: "the apparent anomaly [of the high sex ratios in the late birth orders] is resolved, however, and James's hypothesis of human sex ratio determination is supported when universalistic assumptions of declining coital frequencies with spousal age and marital duration are replaced by more appropriate and population-specific ethnodemographic information."…”

“…A number of anthropologists (Martin, 1994a;Whiting, 1993;Borgerhoff Mulder, 1994;Brewis, 1993;Underwood, 1995) have invoked my hypothesis (James, 1971) that variation in coital rate around the time of conception is responsible for variation in the sex ratio of the resultant births. It would seem odd to me if varying patterns of coital rate with duration of marriage were responsible for the various forms of regression of sex ratio on birth order mentioned above.…”