I have heard that more boys than girls are born during wartime, almost as if Mother Nature “knows” that men are being killed and the male/female balance needs to be adjusted. This seems a bit far-fetched but does anyone have statistics to back it up?
I don’t know but …
This is atechnical paper on birth ratios. It requires a rather sophisticated background in statistics to follow completely but it doesn contain the following interesting statement as to how the author chose his sample:
“For this purpose, I chose the legitimate live births for England and Wales 1950–1969 inclusive (as given in the OPCS Birth Statistics for 1974, Table 1.1). These dates are not arbitrary. The period was deliberately chosen: (i) to start after the wartime perturbations of the sex ratio had ceased [bold added] and (ii) to end before the decline in sex ratios starting in 1973”
The paper didn’t say what that “perturbation” was, but a further search might find some solid data. It looks like there might very well be something to it.
I have no idea if it is the case, but one can speculate that seeing fewer men (or smelling fewer male pheromones) could trigger testosterone production in women, which would make male children more likely.
There are more boys born both during war and peace.
Except for the fact that gender is determined exclusively (at least in mammals) by the chromosomes present in the sperm, not the egg.
Googling brought up this study of gender ratios over the last 250 years in Finland (bolding mine):
Of course, the study seems to state that the phenomenon was already well-known.
Cite? I’d always heard it was the other way around.
Me too.
The article I cited above gave the ratio of boys/girls in the authors data as 0.514.
If I remember correctly boys have a slightly higher infant mortality than girls. And as has been widely reported a shorter life expectency.
Here is the link to the CIA World Factbook. Globally, there are 1.06 male births for every 1 female birth.
http://www.cia.gov/cia/publications/factbook/geos/xx.html
Also, note that that proportion is almost identical for EVERY country, even those locked up in war. I’d have a VERY difficult time believing that, since the rate is the same regardless of the massively varying social, cultural, and economic norms, that something as paltry as a world war could have such an effect. In fact, The Congo (formerly Zaire) which has been at war forever has a LOWER male/female birth ratio. Even Iraq is slightly below average. It’s also worth noting that even in the most Deadly U.S. war, the Civil War, only 4% of males died, meaning 96% came home and returned to makin’ babies after being absent for MAYBE a couple of years at the most.
If there have been significant variations of male/female birth ratios over they years, it would have to be due to some other cause other than war.
David Simmons is indeed correct. More males are born, but due to higher infant moratlity (and, later, higher risk-related mortality in late youth and early adulthood) the ratio typically equalizes or even reverses relatively early in life. [Definition of middle age: when you start calling the 20s “early in life”)
Most popular almanacs have historic birth ratios as part of their data rotation (the set of general interest statistics they rotate in annual editions). I’m an almanac nut [before the web, they were a major source of statistics for debunking), but I’m rather less a fan of scanning and posting GIFs. Here are the ratios for the past 20 years. courtest of the Infoplease almanac. You’ll probably be able to find historic rates for the last century (at least) in the US on your own bookshelf.
Hmmm. Without being able to provide a cite, :o I do quite specifically recall seeing it variously quoted as 111/100 or 109/100 (males/females) in textbooks. Unless the higher figures are for conceptions, and I’m misremembering the higher figures for births when they’re s’posta be conceptions … I’m confused. Because, of course, it’s nearly impossible to know what actual conception rates are, as there are huge numbers of concepti which spontaneously abort (one of the reasons I have for believing that most Christians have got something wrong WRT “life begins at conception” {and I’m a Christian, seriously evangelical and somewhat fundamentalist, but I’ve studied biology, thankyouverymuch}).
[For the uninitiated, “spontaneous abortion” is a medical version of “miscarriage”, but usually refers to involuntary pregnancy termination during the first few (3? 6?) weeks.]
However, I’m fairly certain I recall more than one of my biology profs saying that there are higher birthrates of males than females in pretty much all mammal species (IIRC, birds have a different system than X/Y, but don’t recall enough to explain it; birds are Not My Thing, not least because I’m seriously allergic to feathers - and invertebrates have yet a different system), and the reason is presumed to be because male progeny have higher mortality rates across species lines.
This graph gives the sex ratio of live births in England and Wales for 1838-1998. The increase during the latter part of WWII is obvious, although not as obvious as the increase during WWI and its immediate aftermath.
Interesting chart, and although it does raise questions as to why a homogenous group would drift like, it rather clearly does not prove any link to incidence of male birth and war. Coincidence does not prove causality.
We have to put this all into historical perspective. The period between 1835 and 1914 was not, as the war=male births theory would suggest, a time of peaceful tranqulity for the UK. They had the Crimean War, the Boxer Rebellion, the Anglo-Afghan War (3 of them), and the Boer War, and had troops stationed across the globe. Also, it’s interesting that the post WWI spike and subsequent rise occur in the intra-war period, when there was no fighting. Finally, since the UK has been at relative peace since the end of WWII (Falkland War, fighting the IRA–I DID say relative), and in any case there are far fewer people in the military than there used to be, the ratio should have dropped significantly in the last 60 years, but it only slipped the a bit in the last 20. The rise in post WWII live births could very well be due to improved medicine helping the more marginal male babies to survive. In any case, we’re talking about ranges from 1.04 to 1.06, which are not particularly great.
I’d say that graph combined with the CIA world factbook show that there is not a correlation between male births, or if there is it is very weak. Remember too that through most of human history, our ancestors were in a PERPETUAL state of war, never knowing if Vikings or nomads or the neighboring tribe were about to attack. Short bursts of violence like WWI and II are pretty small potatoes from an evolutionary standpoint.
In fact, one would expect them to equalize just about at the peak time for childbearing. If the ratio is anything other than 1:1 at that point, evolutionary pressures will favor the less-represented sex, and thus tend to bring it back to 1:1.
Are you suggesting that natural selection kills members of a gender who aren’t getting laid? That sure would suck…so to speak.
That’s an interesting theory, but it is based on so many simplifying assumptions that are demonstrably not the case among many mammals or even humans. (I’m not ragging on you. I honestly found your remark interesting) Some points to consider:
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Not all members of a species reproduce. In many species, it’s quite clear that not all members of a species are meant to reproduce (a bull walrus’ mating beach and harem is one of the simpler but less interesting examples).
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The role of the two genders in reproduction and survival to adulthood is not equal. “One-to-one” marriage and “to death do you part” is a limited local cultural ideal, not a selective force. Reproductive rates and postnatal survival to adulthood are often as high or higher with fewerr males than females as demonstrated after WWII (or any major war) when the adult/adolescent male population was depleted by war casualties. After wars, birthrates tend to go up, not down.
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There’s that whole pesky homosexuality thing (pesky for armchair theorizing, but not (I presume) for the homosexuals, and certainly not for me)
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Humans have all sorts of social complications that trump population pressures, like the predominance of males already being seen in India and China, due to deliberate sex selection. The possible effects of this are interesting to consider, but it should be noted that these social believes are thousands of years old, and if the herbal and other sexual selection methods were even modestly effective (not unlikely, given that male/female embryos have variable susceptibility to various harmful effects), we might well expect to see those hypothetical effects in 100+ generations. I’m not aware of any, though there have been many recorded periods of mate scarcity for both those cultures.