Like a Virgin by Prasad, Aarathi (recommended reading txt) 📕

population of women aged sixty-five or older is projected to be eight hundred and twenty-five million.

In theory, this long stretch of sterility in life may be an evolutionary adaptation, because women stand to gain greater genetic benefits in the long term by helping their children to reproduce successfully rather than by continuing to have more babies of their own, an idea called the grandmother hypothesis, first put forward by University of Utah anthropologist Kristen Hawkes. When an older woman becomes infertile, it helps to ensure her longevity – giving birth to babies with big heads via a narrow birth canal is a difficult endeavour at any age, but in older age the risk of death or medical complications is much higher. But the menopause also has a social side benefit: it frees up older women to care for their daughters’ babies rather than compete with younger, more fertile women for sperm. (Of course, this assumes that the menopause marks a change in sexual activity, not just in reproductive capability. And the changes in hormones at this time do, indeed, make a difference.)

Compared to other animals, human babies are markedly dependent on adults (usually, mothers) for an extended period of time, which means that if a mother were to die, having a grandmother around may be key to a child’s survival. Studies of pre-modern hunter-gatherer groups with no access to modern medicine have found that women with a prolonged, post-reproductive lifespan have more grandchildren, and that these children are significantly more likely to survive to adulthood if they have a grandmother’s assistance. No other relatives have a similar effect.

For most mammals, a mother is more important than a father in determining an infant’s survival into adulthood. Homo sapiens are considered to be unique, however, in the extent to which the family has traditionally provided help and care for our young. So opportunities for inter-generational co-operation may have been one of the evolutionary architects of women’s early and prolonged period of sterility. A woman’s reproductive success depended on having a sterile mother by the time she was caring for a brood of her own. The knock-on effects of menopause would have been very positive for a post-reproductive woman (provided, of course, she happened to have had a daughter in the first place). This may be why the menopause happens bang in the midlife of a woman, but nothing similar happens in a man.

The experience of going through the menopause is not simply a question of turning off the hormones that allow egg release and pregnancy; it is essentially a case of organ failure, with the ovaries shutting down completely, and some doctors consider the process to be as much of a medical threat as the failure of another organ, say, the gall bladder or kidney. The hormonal changes affect a woman’s entire physical and emotional well-being. Post-menopausal women are at increased risk for several major diseases, including cardiovascular disease, breast cancer, and osteoporosis. The female biological clock counts down not just to the end of fertility but to the beginning of a new body, with different needs.

Still, although the onset of menopause seems to be an immutable part of nature, it appears to be amenable to manipulation. The incessant ticking can be speeded up or slowed down. We know, for example, that exposure to certain chemicals or radiation from cancer therapies can trigger premature menopause in young women. The menopause also happens earlier in women who smoke cigarettes.

Why, in evolutionary terms, the end of fertility in otherwise healthy women is so clearly marked has long been a great puzzle. A simple solution would be to work within the limits of what human biology allows. Fertility is subject to hormonal regulation, just like it is in every other mammal, so why not just whip up some hormones in the lab and trick the body into reproduction well beyond its ‘sell-by’ date? The production of hormones can be easily influenced by environmental conditions too.

For humans, though, reproduction is also socially regulated, from the acceptability of walking marriages among the Mosuo to the top-down condemnation of having ‘unprotected sex’ with someone who isn’t a long-term partner. And social regulations don’t live in some world separate from our biology. Take, for instance, the way in which sexually transmitted diseases affect fertility. STDs, such as chlamydia, cause infertility – and these diseases are on the rise. Chlamydia has long been known to cause damage to the Fallopian tubes, making women less fertile; recently, it has been discovered that the bacteria hurt sperm too – men aren’t simply carriers of the disease. When men are infected, the bacteria physically ‘sit’ on sperm, gripping on to the sperm’s tail at intervals, which reduces a sperm’s ability to swim to an egg. The bacteria can also trigger sperm death. The jury is still out on whether treating chlamydia with antibiotics makes any difference to sperm health, as men who have had chlamydia can remain infertile long after the bacteria have been cleared from the reproductive system.

These are the easy obstacles. Humans may have a bigger problem.

A woman, even at peak fertility, needs sperm in order to make a baby. But fertile Homo sapiens males may not be with us indefinitely. The male Y chromosome appears to be hurtling down the evolutionary road towards what, some scientists predict, will be extinction. Our age as a species may be a factor in the future of reproduction as well.

The loss of the Y chromosome would certainly put humans in a complicated position. Over the past three decades, since the birth of Louise Joy Brown, technologies have emerged from the realm of science fiction into the reality of our hospitals and homes to make reproduction possible where it had previously not been. But can science get round the problems that come with getting older?

Age gradually yet surely