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鈥淢UMMY, where do babies come from?鈥� It鈥檚 the question that can freeze the heart of any parent, especially because your curious little mite will most likely choose the most public place possible to ask it. No matter what euphemistic answer you mumble, you are likely to have 鈥� tucked away and childproofed 鈥� an understanding of conception that would have stunned even the brightest brains 400 years ago.

Back then it was perfectly acceptable to believe that a woman could give birth to a lamb, or that a cat and a rabbit could successfully cross-breed. Birds, it was known for sure, laid eggs, but bees? Like other insects, including toads, they spontaneously burst into existence in heaps of rotting meat or vegetable scraps. Everyone knew that. After all, Aristotle had said so.

How we progressed from a time when the mammalian egg was unheard of and even the link between copulation and pregnancy was uncertain to the present era of genomic sophistication is the subject of The Egg and Sperm Race, Matthew Cobb鈥檚 erudite and insightful book.

The transition occurred in the late 1600s, a critical moment in the evolution of western thought when the experimental approach was beginning to triumph over discourse as a means of knowing. Thinkers were gaining confidence, learning to trust their own senses over the dogmatic opinions of ancient texts. Hedged in by the ancient Greeks, the Catholic church and a lack of experimental equipment, Robert Hooke, Reinier de Graaf and Marcello Malphigi, among others, were simultaneously discovering both the secrets of sex and development and the scientific method. Analogous to flying an aircraft while building it, these men were intellectual daredevils. Their quest to understand the origin of living creatures played a key role in the development of what we now call science.

Take, for example, Niels Stensen, the Danish-born, Dutch-educated physician and member of the Medici court who was the first to realise that all female animals have ovaries. Or Jan Swammerdam, who studied insect development and ingeniously thought to inject veins with liquid wax to reveal the vertebrate circulatory system. Then there鈥檚 Francesco Redi, the Tuscan court poet who conducted experiments with pots of rotting flesh to determine if flies really do spontaneously generate from putrescence. (He concluded, after several nose-wrenching years, that they do not.)

鈥溈烀ǘ淌悠祍 ate human eggs to see if they tasted like those of chickens鈥�

Cobb鈥檚 narrative is littered with wonderful examples of human creativity and splendidly eccentric approaches to proof. For instance, we encounter male frogs wearing little taffeta shorts to prevent their sperm from coming into contact with eggs, and scientists boiling and eating human eggs (cadaver-fresh!) to see if they tasted like those of chickens.

Then there鈥檚 the clincher. The UK鈥檚 Royal Society 鈥� the motley crew of thinkers who personified the rise of experimental science 鈥� asked Antoni van Leeuwenhoek, a Dutch cloth trader, to make careful observations of semen under the newly invented microscope. He found that it contained multitudinous little swimming things. This discovery put a 150-year kink in the advancing science of development, as two stubborn camps argued over whether eggs or sperm were responsible for babies.

Cobb seamlessly merges biographical detail with social history, providing a fine picture of the worldview of the early investigators of animal development. He never lets us forget that when it comes to the advancement of ideas, perception is key. In the final chapter, Cobb highlights the power of metaphor, both in spreading new scientific ideas to the public and in allowing those ideas to form in the first place. Our ideas about gene function, he reminds us, owe much to the language and perception of electronics. Even if one of de Graaf鈥檚 contemporaries had been able to envisage the role of genes in development, he probably would have been defeated by the lack of an appropriate language in which to express it.