As you report, Ralph Catalano of the University of California at Berkley and his colleagues have shown that stressed mothers spontaneously abort male fetuses (“Girls on Top,” December 19, 2009). In hard times, they argue, daughters are a safer evolutionary bet, as they are more likely to mate and produce grandchildren than are sons. Although these findings are interpreted in terms of major evolutionary stresses, such as famines, the researchers actually focused on mass layoffs in the States. It is interesting to compare these results with earlier findings concerning another major evolutionary stress—war. In evolutionary terms, famine and war go well together. After a war, sons are apparently more prevalent than daughters, presumably because more men than women are casualties of armed conflict. Returning to the research you report, boys are on top following major stresses experienced by their lucky mothers. Which may explain why sons are welcomed with louder cheers than are daughters.