Famines used to result in an increase in girl babies.

Although the shift was small—only a 1% shift—the 1% means a big shift  in the male: female ratio in a large population. When one nation or cluster of nations are affected by the same economic adversity, the shift is obvious.

Why does this happen? The researchers in this study issue a call for more careful study of causes, concluding that biological stressors in women result in fewer males in the earliest stages of pregnancy during hard times.

The stressors being evaluated here are biological, not situational. It is common for people to talk about being stressed out but that is not the kind of stressed out which affects gender of unborn babies.

A friend of mine was what is called a “chronic spontaneous aborter.” She could get pregnant but every time but the pregnancy did not hold beyond three-plus months. When she made it to five months, she was jubilant—only to lose another.  “I hope it was nothing you did,” said a thoughtless person.

No, this is not about what mothers do. It is what adverse, shared events can do to a population of  mothers.

As the abstract from the American Journal of Human Biology says, “Most research describing the biological response to unemployment appears appropriately motivated by clinical or public health concerns and focuses on death, disease, and medical care. We argue that expanding the work to include other outcomes could contribute to basic science. As an example, we use the response to mass layoffs to discriminate between two explanations of low ratios of male to female live births in stressed populations. One explanation asserts that ambient stressors reduce the ratio of males to females conceived. The other argues that the maternal stress response selects against males in utero. We show that selection in utero better explains the observed data. We conclude that human adaptation to the economic environment deserves scrutiny from a wider array of scientists than it now receives.” (Emphasis added)

In light of the economic meltdown of 2009, it appears safe to say that parents-to-be need to be looking more closely at the baby names book for girls.

The Economist

…”The researchers discovered that mass lay-offs did, indeed, lead to fewer boys being born. Over the whole period 52.4% of births were of boys. In some months, though, that fell as low as 51.2%. Teasing out the statistics suggested that the stress of mass lay-offs probably caused these drops, but that the lay-offs in question could happen months after conception. Male fetuses were, in other words, being spontaneously aborted—presumably as a consequence of stress. (Emphasis added)

“That does not mean the original hypothesis is wrong. But it is not the whole truth. The ruthless winnowing of inappropriate offspring can, it seems, also take place well after a fetus has started developing. The next step, according to Dr Catalano, is to measure in pregnant women the levels of hormones known to predict spontaneous abortion, and to work out if these levels vary with stressful events.” (Emphasis added)

Source: The Economist, December 17, 2009

Citation: American Journal of Human Biology, Early View,  Published Online, November 13, 2009