The past

A brief survey of the history of embryology shows that attempts to understand the mechanisms responsible for the structures that emerge in embryos have not had the highest priority among what we would now call developmental biologists. Indeed, the preformationist approach that directed much of seventeenth and eighteenth century thinking implicitly denied that there are morphogenetic problems to solve. Nevertheless, the contributions made by scientists interested in how structure emerges in the developing organism have been responsible for redirecting the subject of embryology when it had been lead down blind alleys by scientists who did not trust or want to believe the evidence of their eyes. This chapter starts by reviewing briefly two such blind alleys, preformationism and the biogenetic law, partly to pay homage to some distinguished developmental biologists who changed how we think and partly to provide some background before we consider the strategies that have governed recent research into morphogenesis.

Preformationism

Aristotle and Harvey, the two scientists whose thought dominated embryology until the seventeenth century, both considered that structure arose in the embryo through epigenesis. This is the view that most if not all embryological structure emerges after fertilisation and is, with some interesting reservations that we will mention later, the view taken today. The mechanisms by which epigenesis occurred were not speculated upon; instead, it was said that the early embryo had a ‘forming virtue’.