One might think that Hitler had more or less done for the eugenic idea

It's hard not to be impressed by the forcefulness with which people pass on their talents (or lack of them) to future generations. It perhaps shouldn't be all that surprising that they pass on their habits of mind, too. Anyway, Charles Darwin was the grandson of a man who thought about selection, and Charles's grandson, another Charles, died in the 1960s having (like his grandfather, I gather) thought about eugenics.

Eugenics (the science or pseudo-science of improving the quality of the human stock) attracted the grandson of another great man. Thomas Huxley (Darwin's first great defender) begat Leonard, who begat (Sir) Julian Huxley. This Huxley and Sir Charles Darwin were both presidents, in their time, of the Eugenics Society.

I'm trying to get my brain round eugenics partly because I'm writing a Radio 4 Analysis programme on the population bomb and the ideas that have been brought to bear on it. The early feminist birth controllers (especially Margaret Sanger in the US and Marie Stopes in the UK) were both keen on contraception for the twin reasons that it liberated women and because its purposes could legitimately include the idea of increasing the quality as well as reducing the quantity of the human gene-pool. I am mischievously delighted that feminist ultra-liberals have eugenics in their thought-baggage.

One might think that Hitler had more or less done for the eugenic idea, and that people who pursued it after the Final Solution must have been nutty. Perhaps the Darwin and Huxley scions were. But I doubt it.

I came across several copies of the Eugenics Society journal from the Sixties in an Oxford bookshop last week. In them, there is evidence of Darwin's seriousness. Even more obviously, Huxley appears to believe that people's choosing not to pass on genes which tend to make offspring miserable cannot be thought absurd. Indeed, is it not exactly what many women have scans for now? He goes further and wonders if it is wrong to think about the way modern societies tend to produce a type of family which seems "to have ceased to care, and just carry on the business of bare existence in the midst of extreme poverty and squalor". These people are, to put it in blunt terms Huxley eschewed, thick, gloomy and fertile.These problem families and society at large would be happier, he says, if they could voluntarily or semi-compulsorily be induced to contraceive.

These are deep waters. And yet one doesn't have to be a rocket scientist to see the problems which might befall a small minority of families when getting on for 100 years of compulsory education seems to have left them with only the dubious joy of having offspring at everyone's expense while filling their heads with high-octane drivel from their video machines.

I am by instinct far too much of a liberal to apply anything like tough eugenic principles to this problem. All the same, it is worth speculating what might happen if family benefit was withdrawn from highly functional middle- income people and applied instead as a small-family bonus to people marooned in failure. No: I see it's impossible. But I wouldn't put it past a more tough-minded generation to contemplate such ideas.

The point is that time really brings extraordinary flips in moral thinking. Natural selection and birth control were first thought important by people who are at the core of the history of modern liberal thinking; both had strands which went towards eugenics, which became the epitome of illiberalism. Who is to say that eugenics will not again appear both liberal and necessary? Or is the larger point that the forces of religion and reaction might hold greater truths, which merely from time to time appear neanderthal?