Joan Smith: It's a funny way of showing you want to be a good father

Fathers' rights are a contemporary obsession, with DNA tests seen as the latest weapon to ensure that men are not cheated out of them by former partners. So pervasive is this view that no matter how low Blunkett sinks in public esteem after two cabinet resignations in less than a year, he is still a notch higher than his former lover Kimberly Quinn, who seems to be regarded with universal derision. This is partly due to the success of organisations such as Fathers4Justice, which portrays men as cartoon-character superheroes, struggling against injustice. That's more or less the line Blunkett took after his resignation as Home Secretary in December, when he characterised himself as a man who had risked everything for the love of his little boy.

Where Fathers4Justice are very modern is in portraying themselves as victims, obscuring millennia of history in which men's attitudes to paternal responsibility have been highly selective; just think of all the children conceived outside marriage by men who then took off, leaving mothers and offspring to disgrace and penury. For centuries, acknowledging paternity was regarded as optional, even when a child had been born, a circumstance confirmed by the bizarre practice of allowing men, until very recently, to donate sperm anonymously. Knowing who your parents are is vital to anyone's identity and the law has belatedly been changed, thanks to an acknowledgement of the effect of enforced ignorance on children. Only last week, a teenage boy made headlines - no doubt sending jolts of anxiety through a few middle-aged men - when he tracked down his biological father using a saliva swab and genealogical information from the internet.

It always amazes me that fathering a child could ever have been taken so lightly, which isn't to say that I welcome the noisy assertion of paternal rights in all cases. I have come across a number of men who have pursued former partners, demanding access to their children, while reluctant to pay a penny in maintenance; while some women have good reason to distrust men who have been verbally or physically abusive. In that sense, DNA tests are a blunt tool, establishing paternity but useless in terms of signalling what kind of father a man might be or how he is likely to behave to his ex-partner. Blunkett's conduct towards Quinn while she was vulnerable - in the public eye and pregnant with her second child - was that of a bully. No one should be surprised by this, given that sentimentality towards oneself and ruthlessness to others are unchanging characteristics of patriarchy, and Blunkett's blunt northern masculinity is nothing if not patriarchal. But there's poetic justice in the fact that he's been undone for a second time, technically for failing to follow the rules for ex-ministers, but also because of his astounding decision to invest in a DNA-testing company. Did it really never occur to him that, in doing so, his family stood to make a substantial profit from people going through similar forms of misery to the one he imposed on Kimberly Quinn?