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Disaster looms in a world full of men


Baby girl

Missing in action: millions of baby girls (Source: iStockphoto)

Pressure is mounting to allow parents using in-vitro fertilisation (IVF) to choose the sex of their child.

This is an emotive issue with many private tragedies at its heart. Like the Melbourne couple with three sons who lost a daughter soon after birth, and then sought to use pre-implantation genetic diagnosis (PGD) to ensure they had a baby girl.

Some insights from evolutionary biology, and a massive tragedy that is now unfolding in Asia, illustrate why the Victorian Patient Review Panel was right to reject the bid of these grieving parents.

When there is a real chance of a baby of one sex (but not the other) inheriting a genetic condition like Duchenne muscular dystrophy, IVF clinics routinely use PGD to ensure that they only implant embryos of the sex that cannot inherit the disease. And so they should. But until 2005, many Australian clinics also used PGD to let parents "balance" their families, or even to simply choose the preferred sex of their child. That is now illegal. But as new sex-selection technologies like sperm sorting emerge, many IVF clinics are lobbying to legalise these technologies — at least for those parents who can pay the hefty fees.

Libertarians argue that if no public money is used to subsidise sex-selection, then governments should butt out. But there are costs of sex-selection that will be borne not by the people who choose the sex of their children, or even by those children themselves, but by the sons of those families too poor to select the sex of their child and by society as a whole.

In most societies, far more women marry upward into wealthier families than downward into poorer families. As a result, daughters born into wealthy families have a harder time finding husbands than their brothers have finding wives (because those wealthy daughters compete with one another and with girls from poorer families for the few wealthy boys). Conversely, sons in the poorest families find it far more difficult to marry than their sisters do (because few girls will stoop to marry the poorest men).

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Those missing daughters

Evolutionary theorist Bob Trivers and graduate student Dan Willard recognised in 1973 that it would make evolutionary sense for wealthy parents to have more sons than daughters and for poor parents to have more daughters.

High school biology tells us that an average embryo has a 50:50 chance of being a boy or a girl, but not everybody realises that in the wealthiest and poorest families, these odds change in exactly the way Trivers and Willard predicted. In fact, billionaires have an average of six sons for every four daughters. The poorest and least empowered mums tend to have more daughters than sons.

Strange as this bias sounds, things usually work out okay because the excess boys produced by wealthy families balance the extra daughters produced by poorer families.

But what happens when sex ratios get massively skewed?

Unfortunately that's exactly what is happening in China and the Indian subcontinent, where strong preferences for sons are culturally ingrained. Diagnostic ultrasound has become a cheap and easy way to tell the sex of a foetus, and both the one-child obsessed Chinese government and unscrupulous doctors in India have made it possible for families to abort foetuses unfortunate enough to be female. In the Indian territory of Daman and Diu, for example, about 141 boys are born for every 100 girls.

In India, the problem is especially acute among urban elites: the wealthy whose sons have good marriage prospects but whose daughters, unable by caste law to marry downward, have to compete for a suitable groom via the extortionate dowry system. This is exactly what Trivers and Willard would have predicted.

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Angry young men


In Bare Branches: The Security Implications of Asia's Surplus Male Population, political scientists Valerie Hudson and Andrea den Boer argue that violent crime, gambling, drugs and the kidnapping and trafficking of women are rampant in places where there are too many men.

"Bare branches" is the Chinese name for surplus men who, unable to bear fruit, move around as anonymous transients without the kinds of ties and obligations to their communities that usually prevent antisocial or criminal behaviour. Centuries of female infanticide have led to several disruptive conflicts (notably the Nien rebellion) caused by bare-branch militias. The tens of millions of excess men in Asia today threaten not only peace and order within those societies but also regional and global stability.

The question of sex-selection of the 10,000 or so IVF babies born in Australia every year is miniscule alongside the tragedy of Asia's missing women. Even if every Australian family using IVF chose only to conceive boys, only 5000 extra boys would be born each year. Whether this is enough to cause major security concerns remains to be seen, but for a foretaste one need look no further than Australia's proud history of alcohol-fuelled violence and recklessness in mining towns.

There is a deeper question of individual liberty here too. Families wealthy enough to afford sex-selection technologies are also biologically disposed to prefer sons. If they do so, their wealthy and well-educated sons will have no trouble starting families of their own. But the sons of poorer parents who conceived them the old-fashioned way will pay the price. Those young men, poor, outnumbered and very angry, will bear the true cost of sex-selection technology. That tragedy will unfold decades from now, and when it does it will be too late to undo. Which is why sex-selection on non-medical grounds should remain banned.

About the author Rob Brooks is Professor of Evolutionary Biology at the University of NSW in Sydney. He studies how sex shapes the evolution of animal and human behavior. This article builds on a chapter in his new book Sex, Genes & Rock 'n' Roll: How Evolution has Shaped the Modern World (NewSouth Books).

Tags: biotechnology, evolution, social-sciences, genetics

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Published 15 June 2011