Having worked as a clinical psychologist - and read as much of the evidence as I can find - for over 20 years, I have concluded that most of our psychology is caused by the particular way our parents looked after us, especially during the first six years of our lives. This column will attempt to shed some light on why you are the way you are.

Oddly enough, my mum did a childcare column in this very newspaper over 40 years ago. Whether she made a pig's ear of bringing me up I will leave for you to judge over the coming months.

At the next wedding you attend take an unvarnished look at the bridegroom and the bride's father. The physical resemblance can be uncanny and the similarities in personality equally striking. Likewise, as you attend second or third marriages, ask yourself if the new spouse is not remarkably similar to the previous ones.

All of us have a very specific 'lovemap', the set of strong preferences for sights, sounds, smells and personality characteristics in a potential mate. Among heterosexuals, genetics have been shown to play little or no part in what these are. Rather, they tend to base much of the topography of their lovemap on the opposite-sexed parent, a prototype for subsequent relationships.

When couples are asked about the way their parents related to them as children, they are more likely to have chosen a partner who relates like their opposite-sexed parent did. How their same-sexed parent related does not predict their partner's attributes.

But the strongest proof comes from a little-known but particularly ingenious study, published in 1980. A sample of 980 Hawaiians was identified, all of whom had parents of mixed race, and all of whom had married twice. If the theory that we are more attracted by attributes of our opposite-sexed parent were true, then the Hawaiians should have been more liable to marry partners who corresponded to the ethnicity of their opposite-sexed parent.

This turned out to be the case, not only for first marriages, but for second ones as well: for instance, a woman with a white father and black mother, was more likely to marry a white man than a black man. Overall, two thirds of marriages were to the ethnicity of the opposite - rather than same-sexed - parent.

If Freud is right, our lovemaps are so tenacious because childhood sexuality is repressed. When feelings are buried they do not disappear altogether, they are only hidden from conscious awareness. They continue to seek expression.

However, it should be remembered that it was not only opposite-sex parents who were sexually out of bounds in your early childhood, but siblings as well. Fifteen per cent of us can recall sexual activities with them, and far more than that probably felt desires which had to be repressed.

I know of no research examining the issue, but I am sure it would demonstrate that repressed sibling lust is at least as influential as parental attributes. So, if your choice of lovers leaves a lot to be desired, it may not be only your mum or dad to blame.

· Write to Oliver James at oliver.james@observer.co.uk