Why the Victorian era are saw a surge in female births and war begets boys

Changes in the way people made love throughout history caused systematic fluctuations in the sex ratio at birth 

Thinking about sexuality in the Victorian era, the famous advice then given to women may come to mind: “Lie back and think of England!” Many decades later, statistics suggest that men and women may have taken the prudish sexual mores of that period to heart, with an unexpected corollary: An historically unique upswing in the share of baby girls delivered.

Since the early days of demographic records, it has been observed that nature produces an approximately five percent surplus of males at birth, which gives way to a more balanced ratio through increased male mortality and war-related losses at marriageable age. The so-called "sex ratio at birth", which in the year 2012 amounted to 105,4 in England, corresponds to the number of males born per 100 females. In practical terms, this means that for every 20 baby girls one extra baby boy came into existence.

Already in 1741, pioneering German demographer Johann Peter Süßmilch concluded that God casts a vote in favor of monogamous marriage with this "pre-stabilized harmony". The male surplus, he wrote in his book "The Divine order in the changes in the human sex from birth, death and reproduction", compensates “for the higher male losses due to the recklessness of boys, to exhaustion, to dangerous tasks, to war, to sailing and emigration,  thus maintaining the balance between the sexes so that everyone can find a spouse at the appropriate time of marriage.”

One odd thing about the sex ratio is that it showed constant, even systematic variations throughout history, says the renowned British statistician David Spiegelhalter in his new book "Sex by numbers", a fine piece of work that accomplishes the feat of jazzing up dry statistics with saucy sex facts and at the same time bringing overheated speculations down to earth with meticulous analysis. 

A look at the official statistics on births in England and Wales from the late 1830s until 2012 (see the chart at the bottom) reveals that the sex ratio underwent wild swings, with a steady decline towards low point of almost 103 (a disproportionate high share of female births) in the Victorian era and glaring peaks at the end of the two World Wars, but also around 1973. Now, as to the increase in the share of male births in the wake of the two World Wars, that smacks of "intelligent design", as if some supernatural force were at work, somehow sensing the demographic gap and mysteriously replacing the males lost in warfare with new baby boys. 

Actually, over longer time periods, evolutionary mechanisms certainly would counteract the demographic distortion and restore a balanced sex ratio. But for one, the rebound happened much too rapidly, and furthermore, extra boys are also born to younger parents, early on in marriage, and to those who conceive quickly. According to Spiegelhalter, this has led some to conclude that, rather than evolutionary pressures, it is the intensity of sexual activity that can, by a small amount, lead to more boys. 

To cut a long story short, there is empirical evidence that heavy sexual activity increases the chances that conception will occur before the most fertile time of the female cycle, as the woman may be pregnant by then. And the data also suggest that, possibly for hormonal reasons, such conceptions are slightly more likely to be boys. "It doesn’t take much imagination to suppose that the ends of wars, with servicemen home on leave or returning home, are associated with fairly intense sex – more babies were born in the UK in 1919 than any other year in history. Put all these together and you get the conclusion – frantic fornication breeds boys."

As to the heightened sex ratio in the early 1970s, this was a period when the age at first marriage and age at first birth reached an all-time low point in the UK and young people excessively engaged in sexual activity. Like with the soldiers returning from the war zone, having more sex leads to the birth of somewhat more baby boys.

Which brings us back to the mysterious surge of female births in the late Victorian period. Could it be that, in the same vein in which heavy sexual activity increases the sex ratio, a  trend towards sexual inactivity lowers it? "Victorian morality" distinguished itself through a set of values that espoused sexual restraint, with an increased condemnation of masturbation and sexual activity in general, repressing any form of sexuality other than penetrative intercourse. And indeed, statistics reflect a steady decline of sexual activity throughout the Victorian period, reaching its lowest point in the year 1898. But as there was less sex going on, conception tended to occur around the most fertile time of the months, bestowing a (relative) excess of baby girls on the Victorians. 

As to the current sex ratio, in recent decades, the "equalizers" of war and infant mortality have largely taken a backseat. In terms of volume, there is now a surplus of men until 60 years of age, which only tips over at retirement age, because women live longer. Together with the prolonged drop in birthrates - which creates problems for males in itself -, this is increasingly making it difficult for men to find a sex partner in the adequate age range, which spells trouble for the future. More on this point here: https://plus.google.com/101046916407340625977/posts/8o3isk7Nc1g

David Spiegelhalter: Sex by Numbers


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