The Historiography of Embryology and Developmental Biology

Biologists have long sought to understand which genes and what kinds of changes in their sequences are responsible for the evolution of morphological diversity. Here, I outline eight principles derived from molecular and evolutionary developmental biology and review recent studies of species divergence that have led to a genetic theory of morphological evolution, which states that (1) form evolves largely by altering the expression of functionally conserved proteins, and (2) such changes largely occur through mutations in the cis-regulatory sequences of pleiotropic developmental regulatory loci and of the target genes within the vast networks they control.

The history of life documented in the fossil record shows that the evolution of complex organisms such as animals and plants has involved marked changes in morphology, and the appearance of new features. However, evolutionary change occurs not by the direct transformation of adult ancestors into adult descendants but rather when developmental processes produce the features of each generation in an evolving lineage. Therefore, evolution cannot be understood without understanding the evolution of development, and how the process of development itself blases or constrains evolution. A revolutionary synthesis of developmental biology and evolution is in progress.