An Amazing 10 Years: The Discovery of Egg and Sperm in the 17th Century
Faculty of Life Sciences, University of Manchester, Manchester, UK
The scientiﬁc identiﬁcation of the key components of sexual reproduction – eggs and sperm – took place during an amazing decade ofdiscovery in the 1660s and 1670s. The names of many of the people involved are now forgotten, and yet their work, and the diﬃculties they faced and the conﬂicts they endured, resonate strongly to the present day. Despite this period of innovation, the respective roles of egg and sperm remained unclear for another 170 years. Why did this take so long? And what did people think before these discoveries? Bytracing the contours of this major milestone in human knowledge, we can also gain insight into our current knowledge, and the boundaries we may be unwittingly trapped by.
The 17th century discovery of the role of egg and sperm in reproduction can be traced to two letters, written 7 years apart, each by a remarkable man who is largely forgotten today. Those letters heralded anamazing decade of discovery that eventually shaped the way we now understand life. ´ In April 1665, Melchisedec Thevenot (c.1620–92), a French patron of the sciences, wrote to his friend Christiaan Huygens (1629–95), a Dutch mathematician and astronomer: ‘We took the opportunity provided by the cold of recent months and applied ourselves to dissections and to investigating the Generation of ´ animals’(Thevenot 1665). The ‘we’ referred to two of ´ ´ ´ Thevenot’s proteges, the Dutchman Jan Swammerdam (1637–1680) and the Dane Niels Stenson (‘Steno’) (1638–86). This was the start of a process of discussion, dissection and experimentation that would soon lead Swammerdam and Steno to the conclusion that all animals – including humans – come from eggs. The second letter was sent 9 years later, inApril 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 thehistory of science: the observation of spermatozoa. To understand why these two letters were so important, 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 maleand 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 ofreasons 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-gatherersocieties, 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...