SO FAR as it can be measured by a sperm count, male fertility fell by as much as 40 per cent between 1940 and 1982, and by 50 per cent in the past 50 years.

A different study from Aberdeen showed that between 1889 and 2002 the average Aberdonian male’s sperm count fell by 30 per cent.

The average British male’s sperm count started to fall at the beginning of the 20th century and has continued to plummet ever since. Many explanations have been given for this, including the presence of female hormones derived from excreted contraceptive Pills and HRT that have passed into the water supply.

These levels may have been high enough to affect male fish but are unlikely to account for human problems as men’s sperm count was already falling by the time the Pill was introduced in the early Sixties.

Better food and therefore more obesity in women bearing male children have been blamed. Alcohol and drugs have also been mentioned as causes. For half a century, tight trousers and Y-fronted pants were thought responsible, all of which keep the testes close to the abdominal wall and thereby defeat nature’s device for keeping the testes low. Nobody denies the importance of keeping the testicles comparatively cool, but few trousers were tighter than those in the 18th and 19th century, and lack of fecundity was not a characteristic of that age.

For fertility, the temperature of the scrotum must be less than that in the abdomen. Just as men with a low sperm count have been recommended to avoid tight trousers or pants and to be careful about hot baths before bed, it seems that they should now be told to put their computer on a table and not rest it on their knees where it can heat the genitalia.

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