Book Review: Generation
I just finished reading Generation: The Seventeenth-Century Scientists Who Unraveled the Secrets of Sex, Life, and Growth, by Matthew Cobb. The title is descriptive of the book, though it is not totally confined to the seventeenth century. In the book, Cobb introduces the reader to a number of researchers and scientists including: Jan Swammerdam, Reinier de Graff, Niels Steno, Francesco Redi, Anton van Leeuwenhoek, and others. The book offers a facinating opportunity to put yourself in the place of these men.
For a topic as fundamental to life as reproduction is, it is remarkable how little humanity understood it until recently. Even the concept of fixity of species is a modern one.Although people all over the world knew that in general 'like breeds like', nobody knew why, and everyone was prepared to accept that there might be exceptions....In this world where like did not necessarily breed like, and where mice could be generated from wheat, there was no space for the idea of 'reproduction'. The word...was not used in its current sense until the second half of the eighteenth century. (pg. 10)
Until the 1600's, understanding of generation was dominated by ancient Greek ideas, particularly those of Aristotle and Galen. But things began to change as people paid closer attention to anatomy and were willing to discard the wisdom of the ancients in favor of observation and experimental results.
However, the scientific method is not a guarantee to an immediate and full understanding, and Cobb details places where these early scientists (an anachronistic word) went wrong in spite of clear experimental results and good logic. By the end of the seventeenth century people were polarized into spermist and ovist camps. For ovists, the egg was the source of generation; something in semen merely activated the egg. (Some dismissed sperm as parasites.) Spermists, on the other hand, thought that the female just provided a nurturing environment for sperm. It would not be until the mid-1800's that this divide would begin to disappear.
There were a number of difficulties in bridging the divide. For one thing, better technology was needed. Before the microscope was invented it was impossible to even see sperm and difficult to see the egg. Cobb also argues that technology provides a conceptual framework with which to understand nature. The frontier of discovery requires new language and analogies to common life.Because it was thought that organisms were like [divinely designed] clocks, a correct understanding of generation would require people to imagine two clocks splitting in half, and then each pair of half-clocks somehow coming together to make a new clock. This would have required not only an unimaginably complex process, it would also have raised the question of how the two half-clocks 'knew' which bit went where. In the seventeenth century this would inevitably have meant a return to Aristotle's 'final cause' explanation. The search for a mechanical analogy would have led right back to a supernatural mind-set--exactly what the scientific revolution was trying to replace. (pg. 226-227)
There are those who are agitated over the materialist assumptions inherent in science, however the history covered in this book serves as a reminder of the remarkable success materialist explanations have had. Materialism may or may not ultimately explain all of life and nature, but its success in displacing mystical or supernatural explanations--a displacement we often take for granted--should serve as a reminder of its importance to science.

