The second letter was sent 9 years later, in April 1674. It was written by Henry Oldenburg (c.1615–77), the German secretary of the Royal Society (Hall 2002) and was sent to a Delft draper, Leeuwenhoek (1632–1723). In the letter, Oldenburg asked Leeuwenhoek to use his microscope to study semen, saliva, chyle, sweat and other bodily fluids. With this inspiration, in 1677, Leeuwenhoek would make one of the most stupendous discoveries in the history of science: the observation of spermatozoa.
To understand why these two letters were so impor- tant, we need to unlearn all that we know about reproduction, beginning with that word. The term ‘reproduction’ was first introduced by Buffon in 1749 (Roger 1997). Up until then, people spoke about ‘generation’, and this was taken to include both how organisms grow apparently from nothing, and how male and female contributed to new life (Cole 1930).
Although the simple answer to the question ‘where do babies come from?’ is fairly obvious – they come out of the female vagina – arriving at an explanation of how the baby got there in the first place proved quite difficult (Cobb 2006a). It seems very likely that early human populations did not know that intercourse led to babies. There are number of reasons for thinking this. Firstly, how could they know? The link between intercourse and pregnancy is not at all clear or immediate – people can easily have intercourse without the woman getting pregnant and the first signs of pregnancy may not be seen for weeks after the act. This surprising supposition is supported by the widespread existence of matrilineal communities in hunter-gatherer societies, which suggests that men’s role in generation was uncertain.
It is possible that the domestication of animals provided the key. In all domesticated animals, mating takes place only during oestrus (Potts and Short 1999). Placing the animals together to allow mating would have been an important step in domestication and in ensuring the survival of the animals and of the human group that owned them. According to an un-testable hypothesis, this could have had two inter-linked conse- quences: it may have revealed the role of male animals (and, by extension, of men) in generation, and also created an economic surplus. And once wealth became widespread, the question of paternity became funda- mental for society.