There were times while reading Count Down that I felt I was going to skip to the final part. Not because I wasn’t gripped – I was – but because I needed a dose of the optimism Shanna Swan wisely promises her readers will be coming at the end. For this is a story of potential apocalypse: the demise of human fertility at worst, the emergence of an unsustainable society of oldies at best.

We assume procreation is a choice. We rest easy, believing we can utilise this natural process at will because, by default, everything is fine with our reproductive systems. It’s an assumption that holds until failure to conceive on demand sends us to the doctor. Traditionally, but not necessarily accurately, more of the blame for a fruitless marriage has been attributed to women. IVF, introduced in 1978, was the first of the assisted reproductive technologies that have helped transform infertility for heterosexual couples and allowed single women and members of the LGBTQ communities to enjoy parenthood. But while we have been celebrating our ingenuity, something far less desirable has been happening.

Swan, an American environmental and reproductive epidemiologist, has spent her long and distinguished career exploring the darker side of the story of human fertility. In 1992, during investigations into environmentally induced birth defects and miscarriages, she read a reputable study identifying a precipitous decline in sperm counts around the world