As we have discussed on many occasions over the past few years on this blog (we promise we will do a ten-year extravaganza post when we get there – only a couple of years to go now!) the demographic story of the 21st Century is not population explosion but population stagnation, ageing and decline (except for Africa). How societies and economies and individuals will react to this are the big unanswered questions.

A couple of months ago I reviewed the book “Empty Planet” which argued that the global population would begin to decline in about three decades and that the current population predictions used by the UN were not to be trusted as accurate. Now there is further reason to think that the current population models are too sanguine. A new five-year project led by Fengqing Chao, a public health researcher at the Institute of Policy Studies in Singapore, has finished cataloguing sex ratios at birth across the world.

Generally, the sex ratio at birth is skewed towards males: for every 100 girls born, 105 are male. This is thought to be because males are generally weaker and more susceptible to death in their younger years and then more likely to die violently when older and are more likely to die before their female counterparts. (For every man that reaches the age of 100 and receives a telegram from the Queen, four women also attain that same milestone.) However, this new study has found that any assumptions by demographers that this natural sex ratio is still being achieved is wrong. Instead, in most regions of the world, sex ratios diverge significantly from the historical norm. In short, there are far too many boys being born thanks to societal expectations, sex-selective abortions and infanticide.

Thus, there are roughly 50 million excess males under the age of 20 in India and China. In China in 2005 the sex-ratio peaked at about 118 boys to 100 girls. That generation of Chinese boys, many of whom have no chance of marriage or family life, is reaching adulthood now. The wave of excess males has thus not yet reached its peak. (Indeed I think our first ever blog post was about the geopolitical concerns surrounding an excessively male generation coming through in China – let us hold our breath over the next few years…) Although these giant countries are responsible for most of the “missing” millions of female births, similar trends can be seen in Europe (Albania, Armenia, Montenegro) and in Africa (Tunisia). Worldwide, this trend is bad news for those concerned about the coming demographic winter. According to Darrell Bricker, one of the authors of “Empty Planet”:

 “If the only part of the population who can produce new kids are women under the age of 45, and a whole bunch of them are missing, it’s going to have an obvious impact on the fertility of a population.”

Further, if current models are mistakenly counting women that aren’t there, that only makes his predictions that much more plausible, he adds.

That’s the bad news. The good news is the skewed sex ratios around the world are on the mend. For example, the sex ratio in South Korea in 1990 was 115 boys for 100 girls. Since then, after a backlash against societal pressure for boys, the ratio has reverted to more natural levels. Even in China the preference for boys is becoming less acceptable and apparently sex-selective abortions are becoming a bit of a taboo subject. But although the trajectory may be in the right direction, it will take decades for countries like China to see more normal sex ratios at birth again.

Marcus Roberts is co-editor of Demography Is Destiny, MercatorNet's blog about population.