a set of assumptions, parents may bias the sex ratio to maximize the yield of offspring that thrive and produce grand-offspring.

Trivers and Willard assume the following: (i) the condition of the offspring at the end of the mother's parental investment correlates positively with the mother's condition during parental investment; (ii) differences in offspring quality at the end of parental investment will persist well into reproductive ages; and (iii.) parental investment will benefit reproductive success of male more than female offspring. They note that, in sexually dimorphic species, males more than females show greater variance in reproductive success. For instance, they cite evidence that male caribou in excellent condition out-compete other males for multiple mates, thereby leaving some males unable to find mates. By contrast, female caribou in excellentfemale (but not male) births shifted to earlier liveborn deliveries. After adjustment for this gestational age shift, the Authors find a decline in the sex ratio among pregnancies exposed to the earthquake at three months' gestation. In a separate study, [@bib2] analyze the odds of a live male birth among Muslim mothers in Michigan who were pregnant during Ramadan. Given that Muslims tend to fast each day during the lunar month of Ramadan, Almond and Mazumder use the timing of Ramadan as a proxy for nutritional disruption among pregnant women with a reported Arab ancestry. In their intent-to-treat analysis, they find a 26 percent decline in male (but not female) births among Arab mothers with peak exposure to the Ramadan fast in the first month of gestation. The