When first examining animal development in Chapter 13, we noted that a pioneer of the subject of embryology was the Italian Hieronymus Fabricius, whose studies on the development of the chick were published posthumously in 1621. This work can best be considered as descriptive embryology – it involved a focus on a particular animal and gave as detailed a description of its embryogenesis as the techniques of the time would allow.

It was not until about two centuries later that embryology became truly comparative. This aspect of embryology is clearly related to evolution, as was recognized by Darwin, who, in 1859, devoted part of chapter 13 in On the Origin of Species to their relationship. An often-quoted statement that Darwin makes there is: “community in embryonic structure reveals community of descent.” We might do well to examine this statement carefully, to try to come up with a modern version of it, and to see what course of logic such an attempt will set in train.