Endless Forms Most Beautiful

It is a truism of modern biology that every animal has developed from a single fertilized egg cell. Essentially all cells of the grown animal contain copies of all the genetic material in the original cell. How the cells of the fully- formed body come to express only those genes appropriate to its tissue type and location in the body has been the fundamental question confronting developmental biology for many decades. How the development process produces a spectacular variety of species sharing a relatively small number of basic body plans is the question addressed by the emerging science of evolutionary developmental biology or “evo-devo” as it is known to its practitioners.

In Endless Forms Most Beautiful: The New Science of Evo- Devo and the Making of the Animal Kingdom Sean B. Carroll recounts how the occasional appearance of mutants and monsters throughout the animal kingdom led to a systematic study of mutations in fruit flies and the identification of a small group of “toolkit” genes, together with the existence of molecular switches which control the expression of these genes and enable the cell to function appropriately in its environment. Some of these genes appeared at least 600 million years ago and have undergone very little change as species have evolved. The same (or very similar) toolkit genes are responsible for the appearance of human arms, bird wings, and insect legs. The discussion necessarily requires careful reading, but is clear and accessible. It is also well- illustrated.

Evo-devo has helped to resolve one of the major intellectual rifts in biology, that between those of the molecular persuasion and those who study form and function in species, living and extinct. The process of evolution and its molecular genetic underpinnings is the central explanatory frame work of biology today, and Carroll closes his book with an argument for making it the centerpiece of biology education as well.