Chelsea Kaplan’s Musings About Life... After Birth

How many boys have not been not born?

To be precise, a research team from the University of California, Berkeley, School of Public Health calculated the number of frail male fetuses that were spontaneously aborted by mothers facing economic insecurity. Looking solely at the state of California between April 1995 and December 2007, they estimate the number is just over 3,000.

Their paper, “Selection in Utero: A Biological Response to Mass Layoffs,” has just been published in the American Journal of Human Biology. The researchers, led by Ralph Catalano and Claire Margerison Zilko, write that the previously reported health effects of economic insecurity may “represent only the tip of a more fundamental ‘adaptation iceberg.’”
Specifically, their research supports the argument that when women receive signals that times are tough, their bodies retain the tendency, shaped over thousands of years through natural selection, to reject offspring less likely to survive.

To our ancient ancestors, those signs would presumably be signals of impending drought or other natural disaster, which would indicate a coming food scarcity. Catalano and colleagues concluded the closest thing we have today is the announcement of mass layoffs at major employers, which impacts “the degree to which the larger population perceives a threat to its economic security.”

Such threats are bad news to small male fetuses because “a relatively large fraction” of them fall near “a critical rank below which gestations spontaneously end,” the researchers explain. If they are born, these small males are more likely to die than larger infants and females of equivalent size.

The researchers examined California’s ratio of male to female births from mid-1995 to the end of 2007 and compared it to the federal Labor Department’s monthly statistics on mass layoffs in the state. The government reports a mass layoff has taken place when 50 or more people file for unemployment insurance from a single company over five weeks.
After doing some complex calculations, they estimated that news of impending mass layoffs “predicted the loss of 3,090 males in utero” during the 61 months (out of the 141 they examined) in which unemployment claims exceeded the expected number.

The male-female birth ratio generally favors boys (who are born at a rate of about 1.05 for every female), but the ladies catch up later in life, since they tend to live longer than men. Catalano’s research touches on that issue as well. “Males from low sex-ratio birth cohorts appear to enjoy relatively longer life spans on average,” he and his colleagues write, “perhaps due to ‘culling’ of the frailest among them in utero.”