An article in the WSJ,
New Light on the Plight of Winter Babies, discusses the work of two economists who attempted to solve the winter birth conundrum. Births in winter have been linked to
schizophrenia,
brain tumors,
asthma, and
socioeconomic disadvantages. The question is why. various explanations have been offered, such as parasitic infections or vitamin D intake. The new explanation: human biodiversity.
The two economists examined birth-certificate data from the Centers for Disease Control and Prevention for 52 million children born between 1989 and 2001, which represents virtually all of the births in the U.S. during those years. The same pattern kept turning up: The percentage of children born to unwed mothers, teenage mothers and mothers who hadn't completed high school kept peaking in January every year. Over the 13-year period, for example, 13.2% of January births were to teen mothers, compared with 12% in May -- a small but statistically significant difference, they say.
So, women with lower IQs and lower future time orientation tend to bear children more in winter than other women. In turn, why these women would tend to give birth in winter remains a mystery.
Ms. Buckles and Mr. Hungerman aren't entirely sure yet. Perhaps it has to do with fluctuations in employment; married women tend to conceive when unemployment is higher, research has shown. They also speculate it might be due to cooler temperatures in springtime, which don't adversely affect the fertility of poor parents, who may not have air conditioning, like hot temperatures do. Or they wonder if there might even be a "prom" effect at work. January is, after all, about nine months after many of those soirees.
The difference in births is small but statistically significant, but I'm at a loss at even imagining any biological factor. Nevertheless, it appears that the season of birth doesn't matter, it's who the mothers are.
OT:
ReplyDeleteDennis, they are looking for a new blogger at 2 Blowhards. I will be happy to nominate you if you'd be interested in the position. No dinero in it, but lots of additional readers. They don't mind if you keep your own blog as well.
My first thought when I read that was that there could be differences in hormonal responses to changing weather -- basically, some women are more responsive to the cues of mating season starting.
ReplyDeleteSo, low-status women respond quickly to the cues that mating season has begun. January births were conceived in April, giving spring enough time to kick in, and for the women to go out courting males.
High-status women could have a less intense response to the cues of spring. Or perhaps they have the same hormonal response but are better at controlling their impulses. They apparently delay copulation until after the heady days of spring and summer are nearly done -- May births were conceived in August.
A way to test these ideas -- different hormonal responses vs. same hormonal response but different impulse-checking abilities -- would be to measure womens' testosterone across the seasons. When spring begins, we might expect both high and low-status women to have higher T levels than before, motivating them to go out there and find a mate.
If the % change in T were different, that would imply some basic difference in hormonal response to signs that the mating season has begun. If the % change were similar, that would imply a stronger control of impulses among high-status women.
Spring is in the air!
ReplyDeleteI was born in early January and have been troubled to one degree or another by asthma -- which I would describe as idiopathic, i.e. I and they (doctors) have never been able to pin down exactly what causes it -- for most of my life; none of the other characteristics (unwed mother etc) apply to me.
ReplyDeleteI remember reading several years ago (sorry, don't remember where) of study of seasonality of births prior to the 20th century which found that human births historically peaked duirng the winter months of each year. The authors concluded that there is a human "rutting season" in the spring months. Before the widespread use of birth control, there was evidently no class distinction in this pattern.
ReplyDeleteToday, a reasonable hypothesis might be that women or couples with higher IQ's and higher future time orientation no longer show this pattern due to artificial birth control and family planning, while births to lower IQ women continue to show the natural biological tendency.
Yeah that one's easy.
ReplyDelete"A young man's fancy lightly turns to thoughts of love."
It's just echoes of mating season. An aggravating factor: in spring, women can stop wearing burka-like overcoats and start being provocateurs again. In university, I really enjoyed the walk to class on dewy spring mornings.
Echo agnostic's point about the reaction to impulse.
Rick: Thanks. I just read the 2 Blowhards post saying that they need someone, but I don't think I could handle 2 or 3 posts a week. I'm having a hard enough time maintaining my own blog; not to speak of the fact that I think those guys over there are way better than me.
ReplyDelete"a small but statistically significant difference, they say." Ho hum: the point was made that they have essentially a complete set of data. So they are dealing with statistical "populations", not with samples from populations. So the phrase "statistically significant difference" is invalid, isn't it?
ReplyDeleteTwo and half years ago I found no meaningful relationship between IQ and birth month in the GSS. This matched Helmuth Nyborg, who found no relationship between birth month and IQ in the NLSY and another large dataset.
ReplyDeleteIt seems that historically, there is also a disproportionate share of winter births among some of the West's creative geniuses:
ReplyDeletehttp://www.gnxp.com/blog/2006/02/genius-germs.php
In spring, the girls and boys wear less, look hotter, and suddenly it becomes possible to bang on the grass, in the cherry tree, on the side of the car, and so on and so forth. This is likely to have a greater effect on females with poor impulse control. Nine months after spring, it is winter, and women with poor impulse control will be popping out little bastards
ReplyDelete