In The Ovary of Eve Pinto-Correia takes as her subject not the battle between preformation and epigenesis, but preformation in its own right, and in particular the debates between the ovists (who argued that the organism was encased in the egg) and the spermists (who favoured the sperm as a container). Inspired by Stephen Jay Gould (who contributes a foreword), she exhibits a similar breadth of learning. Her account ranges not just over the history of embryology but over science more generally, and over the broad sweep of culture and ideas.
Malebranche and Swammerdam were the founding "fathers" of ovism. In their studies of frogs and chickens and insects, they thought they could see the future parts of the adult folded up inside the egg (Swammerdam probably discovered insect imaginal disks but interpreted them wrongly). Prominent later ovists included von Haller, Bonnet, and Spallanzani. But the connection of eggs with reproduction is quite obvious, and ideas about it can be traced back to the Egyptians and the Greeks, as well as cross-culturally.
Spermism originated later, with the microscope and the work of van Leeuwenhoek and Hartsoeker. Later spermists included Astruc, Boerhaave, and d'Agoty. Sperm were seen as little animals, as tadpoles or worms, and hence held in low regard by many. Another problem spermism faced was how to explain why so many sperm were wasted. In the 18th century this problem was worsened by a growing hysteria over masturbation ("the great fear"), started by the pamphlet Onania and propelled by Tissot's campaigns. There was also a reluctance to accept a physical role for sperm in reproduction, with many assigning them a spiritual role instead, acting through an immaterial aura seminalis. This had parallels with the doctrines of the Immaculate Conception and the Holy Spirit.
Commonly attributed to the spermists (as a form of mockery) is a "wounded warrior" theory, in which conflict between sperm is responsible for the birth of monsters. This would have been a powerful argument for spermism if monsters had been considered a major problem for preformation. But while teratology (the study of monsters) was of widespread interest, the difficulties posed by monsters (and by the ability of some organisms to regenerate from parts) afflicted epigenesis and preformation alike. And in fact the "wounded warrior" idea was retrospectively written into the history of spermism.
The use of the word "homunculus" to describe human-like sperm (commonly accompanying drawings attributed to Hartsoeker) has a similar history. The word had long-standing negative associations, resulting from its connection with attempts to create life, so it would have been surprising if the spermists had chosen to use it. In fact they avoided it quite scrupulously, and its association with spermism was a creation of later writers.
In the mid-eighteenth century, Buffon and Needham revived the theory of spontaneous generation; this time it took the form of a Vegetative Force. In response Spallanzani carried out a long series of experimental tests of the role of sperm in reproduction (including the famous "frogs in boxer shorts" experiment), in the process making important advances in experimental technique (among them the first artificial fertilisations). But Spallanzani remained an ovist, despite his demonstration of a crucial role for sperm in reproduction.
One advantage for ovism lay in the shape of the egg. The sphere represented perfection and was therefore highly favoured — as can be seen from the history of theories of planetary motion. But a countering disadvantage was that eggs came from the female of the species, consistently considered inferior in the West, along with the left side.
Numerology already had a long history in Western culture, going back to the Pythagoreans, but the invention of the microscope and the discovery of the very small ushered in a period of fascination with the resulting large numbers. Hairs, pores, insect eyes, and other body parts were counted and their numbers calculated with. But preformation offered a particularly fertile field for the numerically minded: immense numbers of generations and encased organisms, and geometric progressions in development.
The debate continues today: some of the issues argued over by the preformationists still bedevil modern developmental biology. Their traces can be seen in the flaws in the science of Jurassic Park and in the difficulties faced in cloning vertebrates and especially mammals (an area in which there have been notable achievements since The Ovary of Eve was printed). The turn of the century debate between Hertwig and Weissmann (a preformationist) and the rise of genetics (traditionally identified with preformationism) illustrate the ongoing complexities of the subject.
The story of preformation is a grand tale, and Pinto-Correia gives it its full due. She often digresses — she includes a long account of astrological and metallurgical sex symbolism, for example — and she includes comparisons with ideas about reproduction from non-European cultures, but everything is woven together into a unified picture. The result is a tour de force, a penetrating portrait of an entire scientific milieu. The Ovary of Eve will be appreciated by many who have never thought about biology, not just by historians of embryology and reproductive biology.