The Economist magazine pointed us to a study just published in the Canadian Medical Journal. Canadian mothers born in South Korea bore as their first children 105 baby boys to every 100 baby girls. That is perfectly normal. It appears to an evolutionary adjustment that the human race has made. It seems that more boys that girls die before reaching adulthood – perhaps they are more adventurous, climb more dangerous trees, ride more fast motorbikes; or perhaps they are just more susceptible to childhood illnesses. Whatever the reason, the normal human birth ratio, worldwide, of about 105 boys to every 100 girls seems to even itself out by young adulthood to leave about one girl for every boy, and one boy for every girl, to fall in love with and to have children with and live happily ever after.
This might seem stunningly obvious; but the founding father of modern statistics, R.A. Fisher, gave his name to the principle that a roughly equal number of boys and girls is evolutionarily the most advantageous way of doing it. He does not seem to have invented the idea (if anyone did, Darwin did); but some Fisher fans claim it is "probably the most celebrated argument in evolutionary biology". I remain to be convinced; it still seems blindingly obvious to me.
Bu it does lead to some curious byways. Whether societies that are polygamous end up in time with the same sex ratio is a question to which I do not know the answer: would old-style Mormons, allowed four wives each, have evolved in time to produce four times as many daughters as sons? A parallel is in mammals like deer, where an alpha male controls a harem of dozens of females. Perhaps a deer expert can tell us if the same number of male deer are born as females.
Returning to the human species, I said that the global adult sex ratio is about even. That is not quite true. There are actually 101 men in the world to every 100 women. (Source: CIA factbook.) I cannot tell you why. But the whole thing can of course all go horribly wrong. Great wars kill more men than women – in Europe there was a huge deficit of men for girls to marry after the First World War - in Britain alone 2 million women of that generation had to remain lifelong spinsters. In Bavaria after world war two the surviving male-to-female sex ratio in the German state of Bavaria was 0.60 for young twenty-something-year-olds. Another reason it can go wrong is in cultures where boys are prized and girls are considered liabilities. Historically, girl babies used to be left on mountainsides to perish.
The practice still persists, but brought up to date. Today cheap and affordable ultrascans can easily tell the sex of a foetus; and selective abortions - if it’s a boy, keep it; it is is a girl, don’t – can occur. It happened widely in China from the 1980s onward - motivated in part by the one-child policy; if you are only allowed one offspring, the pressure to ensure that it is a boy is all the greater. See Significance magazine here - Too many males in China - for an analysis of the consequences: 120 boys to each 100 girls leaves very many young men with no hopes of marrying who turn to turn to crime and thuggery instead. But China has outlawed abortion on grounds of gender; it still continues, but illegally – and since abortion itself is easily available, it is hard to prevent.
There are countries where gender-selective abortion happens and is legal. One of them, if you can remember back to the start of this article, is Canada. And, while first children of mothers of South Korean extraction show a normal sex ratio, their second children show a very different sex ratio, of 120 boys to every 100 girls. The pattern is similar for some other ethnic groups: Indian, Filipina and East Asian mothers have second-child ratios of 110 boys to 100 girls. For third children in Ontario for mothers of Indian extraction it is even more extreme, at 136 boys to every 100 girls.
Why it is happening is not part of the study. What if anything should be done about it is for Canadians to work out. Some have suggested changing their liberal abortion laws; others, that doctors should not tell parents the sex of their foetus until the 30th week of pregnancy. But China has at least tried to make illegal the modern equivalent of leaving girl-babies on mountainsides because they were not boys. Should Canada follow suit?