2 - Exemplars

Summary

The amazing thing about … development is not that it sometimes goes wrong, but that it ever succeeds.

– Veronica van Heyningen (2000)

Textbooks of developmental biology are rife with examples of what makes development such a fascinating science. In this chapter, I discuss but three. We will return to these examples in later chapters as we explore the nature of development and its evolutionary significance, but their introduction here gives us some signposts of significant events and achievements in the study of development over the past 125 years.

The exemplars I have chosen are not necessarily the most groundbreaking achievements of developmental biology – I am not quite sure how one would select the most important ones. As will become evident, though, they are both important and heuristically and rhetorically useful, and they well represent the three elements of the title of this book: embryology, epigenesis, and evolution.

EMBRYOLOGY: ROUX AND DRIESCH

To set the stage for Chapter 3, and so to illustrate the contrast between preformation and epigenesis, it is useful to review several important experiments undertaken in the early years of experimental embryology in the nineteenth century. The experiments in question are those of Wilhelm Roux (1850–1924) and Hans Driesch (1867–1941).

Roux's experiments, some of the first conducted on an embryo, were indeed pathbreaking, and they are also amongst the most well-known experiments in embryology.