Ross Clark Ross Clark

The incest trap

When one man can anonymously father up to 800 babies, what happens if those children meet?

It is hard to think of a code of behaviour which is common to all societies on earth, let alone to most other species too — except, that is, for the avoidance of incest. Even cockroaches have developed a breeding strategy that prevents them mating with their own siblings. And yet as we understand more about the genetic dangers of inbreeding, so the social infrastructure that guards against it is being dismantled.

In the 40 years since the birth of Louise Brown, the world’s first test tube baby, births by IVF have become routine — almost 2,500 a year using donated eggs, sperm or both. And yet there is virtually no guard against the children growing up and accidentally breeding with half-brothers and sisters of whose existence they are unaware.

The failure to develop such safeguards is serious because the risks of genetic abnormalities from incestuous conceptions are so high. In 1971 the Czechoslovakian Academy of Sciences studied 141 children born in such relationships and found that more than half had some kind of health problem, while 42 per cent had severe birth defects and 11 per cent were mentally impaired.

There has always been a risk of brothers and sisters beginning relationships unaware that they are siblings — or more likely half-siblings. Children born as the result of affairs may have no inkling of who their real father is. A geneticist who works in a west London hospital told me that in as many as one in ten cases of children investigated for various reasons there is no genetic match between the child and the man who thinks he is the father.

But that is a risk which is hard for government to guard against. The increasing number of children who are conceived with donor eggs or donor sperm — an activity that is regulated by the state — is quite another matter.

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