PCOS: fertility in famine

With the polycystic ovary syndrome (PCOS, discussed on WebPage 11) we have another example of an at least partly inherited condition that diminishes fertility (by lengthening the menstrual cycle and reducing the frequency of ovulation), thus advantaging the evolution of reproductive success.

But Dr John Eden, a reproductive endocrinologist at the Royal Hospital for Women in Sydney, believes that PCOS could have had more direct evolutionary advantages in some special circumstances.

In times of starvation, most women's periods stop and they become infertile as they lose weight.

But would it be useful for some women to show the opposite?

Say a famine went on for more than a generation -- if all women stopped ovulating the population would be wiped out!

You can imagine that at times of prolonged famine (and subnormal weight), some women -- a minority, perhaps -- would advantage the population by retaining their capacity to reproduce, even at the expense of decreased fertility in times of plenty.

This is exactly what happens among women with PCOS, who may have irregular periods (and ovulations) at normal body weight (and who stop ovulating completely as they gain weight into the realms of obesity), but who will usually ovulate well if their weight falls considerably below what we call normal.

This historical legacy could explain why perhaps as many as one in five of all women have evidence of polycystic ovaries when the condition is looked for carefully.