What I wonder about is why we love our children so asymmetrically, so entirely, knowing that the very best we can hope for is that they will feel about us as we feel about our own parents: that slightly aggrieved mixture of affection, pity, tolerance and forgiveness, with a final soupcon - if we live long enough - of sorrow for our falling away, stumbling and shattered, from the vigour that once was ours.

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Our love for anything cannot be explained by our possession of genes, any more than our love for football can be explained by our possession of feet. … It is not that the big emotions we feel - love or lust or loyalty - are more mystical than their biological origins but exactly that they are far more material, more over-loaded with precise dates and data, associations and allegiances, experiences and memories, days and times.

The mechanism of life may be set in motion by our genes, as the mechanism of football is set in motion by our feet, but the feelings we acquire are unique to our own weird walk through time.

My own best guess about the asymmetry of parental love lies in a metaphor borrowed from the sciences. Merely a metaphor, maybe, but one that - as metaphors can - touches the edge of actuality.

One of the rules of mathematics and physics, as I - a complete non-mathematician - read often in science books, is that when infinity is introduced into a scientific equation it no longer makes sense. All the numbers go blooey when you have one in the equation that doesn’t have a beginning or an end.

Parental love, I think, is infinite. I mean this in the most prosaic possible way. Not infinitely good, or infinitely ennobling, or infinitely beautiful. Just infinite. Often, infinitely boring. Occasionally, infinitely exasperating. To other people, always infinitely dull - unless, of course, it involves their own children, when it becomes infinitely necessary.