The geneticist Professor Steve Jones said this week that the human species has reached the end of the evolutionary road - the process has ground to a halt and we are as evolved as we are ever likely to become.

Although, so far, no one has got around to blaming NHS GPs for this, I might as well get in with a pre-emptive confession. It's all my fault.

Natural selection, the process that gives better-adapted creatures a higher probability of survival, is failing because of my efforts to improve survival of the unfittest, to redress the balance. How am I supposed to deal with this paradox?

My duty as a doctor is to give the patient the best possible advice, based on his personal circumstances; obviously to pack up the fags, live long and prosper. If I extend my remit to include the future of mankind as a whole, I've got to tell him to put up with the impotence, chest pains and monkey breath and to procreate for all that he's worth.

He may die prematurely as an emaciated empty husk, but he'll have done his bit for humankind.

And what if his heroic efforts resulted in an evolutionary reversal, sending human beings back to the Stone Age? Trust me, in Southend nobody would notice.

Example. You might think that it would be a good thing for humanity if I told blokes that cigarette smoking lowers their sperm count and causes erectile dysfunction.

If they were to take the message on board and give up, they would end up with a sperm count in the billions and an erection that could crack paving stones. Surely Prof Jones would agree that this would make them ideal prospective parents.

Actually, from his point of view it is counterproductive. The human race has become the superpower that is today by carrying a host of genetic mutations in its collective gene pool. These mutations may make certain individuals more able to survive in a hostile environment than others.

This select group then goes on to have lots of babies, pass on its seed, and, bingo, the human species has climbed another rung of the evolutionary ladder.

Taking this into account, the last thing Prof Jones wants is handsome virile men impregnating beautiful fertile women, combining two flawless gametes to produce a perfect embryo. There's so little chance of a genetic mutation that it's

not worth considering the possibility that their child could go on to father the Earth's next dominant life form. He'll probably just get a job as a model for Dolce & Gabbana.

If evolution is to get the jumpstart it needs, the Sunday Sport-reading labourers with protruding foreheads, nicotine-stained fingers and flaccid genitalia have to carry on smoking and deliver large portions of mutant three-headed spermatozoa to their partners into middle age and beyond - if they live that long.

The combined effects of ageing and smoking result in far more genetic mutations and there's a billion to one chance that their DNA-reworked offspring will take homo sapiens a couple of rungs up the evolutionary ladder, even if they need to improvise with a well-thumbed copy of Nuts or FHM to achieve a pregnancy.

Darwinian evolution doesn't take prisoners. People who don't master the maths and physics involved in calculating the speed of oncoming vehicles end up underneath the cars they were trying to dodge.

Saving people from themselves may be an uphill struggle, but at least I'm working for the good of the species.

And for those people who say that doctors like to play God, we don't. We do it only because nobody else volunteers. And it gives us a watertight reason not to work on Sundays.

Times recommends

• How to solve the big style questions
• Aids in Africa: ‘It is the staff who really inspire you’
• Video: How to do Beyonce's 'Single Ladies' dance