If scientists from Mars were to study the human male’s reproductive system they would probably conclude that he is destined for rapid extinction. Compared to other mammals, humans produce relatively low numbers of viable sperm – sperm capable of making that long competitive swim to penetrate an unfertilized egg.
As many as one in five healthy young men between the ages of 18 and 25 produce abnormal sperm counts. Even the sperm they do produce is often of poor quality. In fact only between 5 and 15 per cent of their sperm is, on average, good enough to be classed as “normal” under strict World Health Organization rules – and these are young, healthy men. By contrast, more than 90 per cent of the sperm of a domestic bull or ram, or even laboratory rat, are normal.
Human males also suffer a disproportionately high incidence of reproductive problems, from congenital defects and descended testes to cancer and impotency. As these also affect fertility, it’s a minor miracle men are able to sire any children at all. In fact, an increasing number of men are finding themselves childless. Among the one in seven couples now classed as infertile, the “male factor” has been found to be the most commonly identified cause.
Full story: Out for the count: Why levels of sperm in men are falling – Science, News – The Independent