Last week a mate of mine, with the look of the proverbial condemned man on his face as his wedding loomed, asked: 'What actually predicts which marriages will end in divorce?' This would be my specialist subject on Mastermind (as my poor friend soon discovered). You have to start with the basics.
The fundamental cause of the huge increase in divorced and out-of-wedlock parents is very largely socio-economic. This is simply proven by the facts.
The number of divorces in 1857 was a gobsmacking five; that was the last year in which it required an act of parliament to get divorced. The rate had crept up to 590 in 1900, but it was still only 4,000 by 1930. It did not really rocket until the 1960s, stabilising around the 165,000 mark in the 1990s - 280 times higher than in 1900.
Such a massive change could not possibly be caused by genes because it takes millennia, not centuries for new genes to become widespread. That has not stopped the authors of a couple of studies of identical twins claiming that the propensity to divorce is half heritable.
But though some regular readers may have concluded that I like to blame everything on how 'They fuck you up, your mum and dad', I do have a sociological bent as well.
Right-wing commentators incorrectly blame the rise on the liberalising of the divorce law in 1969. It was merely a rubber stamp legitimising a trend that was already well established: the rate had not risen during the 1950s, but it doubled before the new law in the 1960s and continued to do so every decade until the 1990s.
Where state intervention did play a decisive role was in offering legal aid. It enabled couples from low-income classes to afford the split, especially dissatisfied wives. In 1950, an estranged wife from a poor family was at grave risk of total penury. By 1966, one third of all divorces were families with unskilled manual professions.
Also, the stigma against working mothers - as well as against the divorced status per se - was slowly eroding. Court instructions forcing husbands to fork out, combined with a greater acceptance of working mothers, meant that lone ones could get by on their own, financially, for the first time.
But above all, it is hard to deny that feminist thinking played a very significant role. Whether at school, at work or in bed, there has been an almost moral imperative on young women to seek something better and, by implication, to be dissatisfied with what they have got. No wonder that in three quarters of cases, it is the woman who begins divorce proceedings.
Of course, this has generally been for better, but in some cases, it has been for worse. The new freedoms of women have given them the chance to make some very bad as well as good choices. And here we return to what PG Wodehouse called 'The psychology of the individual' to explain why some of us and not others add to the divorce statistics - next week's subject.