© Peter Watson 2017  he idea which follows – at some length – explores an important remaining mystery of our ancient past. It is a theme fundamental to our humanity and the psychology of everyone. The mystery is this: when did ancient peoples first discover the link between sexual intercourse and paternity? Why is this important? What follows attempts to explore the whole issue. But first a caveat. Anything relating to ancient history must – to an extent – be speculative. I am presenting what follows as part-speculation, part-based on archaeological and anthropological research as I have been able to discover it. And I am asking readers either to shoot down the idea, because they have evidence that contradicts or vitiates my argument. Or, to provide extra evidence that makes the account stronger. I am quite prepared for new evidence to lead either way.  In the late 1990s, when I interviewed the New York-based anthropologist, Randall White, as research for my book A Terrible Beauty (The Modern Mind in America), he made the astute observation that a time must surely have existed when early peoples had not made the link between intercourse and birth, when life would have been very different psychologically and sociologically. The duration of human gestation (280 days) is just too long to have enabled early peoples – especially hunter-gathers, constantly on the move – to have easily spotted the link. Until that time, what must have seemed the random occurrence of birth would have been both disturbing and miraculous in equal measure. A case will be made in what follows that the discovery of fatherhood was the greatest intellectual, psychological and social breakthrough of all time, a fundamental change in perspective that totally transformed our understanding of ourselves and produced the greatest advance in social, religious and economic life that has ever occurred. The argument combines archaeology, theology, palaeontology, economics, animal husbandry and physiology in what is admittedly an ambitious synthesis. T