By taking steroids to improve their physiques and anti-baldness pills to decrease hair loss, men are unwittingly impacting their fertility.
The evolutionary findings are described as the Mossman-Pacey paradox, after the two scientists who first uncovered it.
It has been the cause of a lot of grief amongst couples trying to conceive.
The paradox was first discovered when Dr James Mossman, now at Brown University, United States, noticed that some of the men coming in for fertility treatments were “huge”.
"They are trying to look really big, to look like the pinnacles of evolution.”
"But they are making themselves very unfit in an evolutionary sense, because without exception they had no sperm in their ejaculation at all." Dr Mossman told the BBC.
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Professor Allan Pacey added: "Isn't it ironic that men go to the gym to look wonderful, for the most part to attract women, and inadvertently decrease their fertility."
Anabolic steroids - which are quite often used by bodybuilders - mimic the effect of testosterone. Many men use them to increase muscle growth.
They trick the brain’s pituitary gland into thinking there’s something wrong with the testes.
The glands respond by shutting down production of FSH and LH hormones. These are the two key hormones needed to encourage sperm production.
The scientists didn’t just stop at steroids. They have also noticed a pattern in men who use finasteride.
Finasteride is a drug used to combat male pattern baldness. It changes the way testosterone is metabolised in order to limit hair loss, but side effects include fertility problems and erectile dysfunction.
Dr Mossman warned that while the use of these drugs could make you more attractive, it could turn you into an “evolutionary dud”.
They suggested that 90% of steroid users are likely to become sterile and admitted that baldness is more “hit and miss” but because of an increase in sales, the number of issues is on the rise.
The scientists suspect that killing your fertility in a bid to become more attractive to the opposite sex is a problem unique to human beings.
"It keeps cropping up in clinics and the message is not getting out to young men that it's a problem and a bit of info could save them a lot of heartache." Professor Pacey concluded.