A DECADE OR SO AGO, molecular biologists, “indoor” laboratory-oriented folks like myself who played with DNA, and paleontologists, “outdoor” field scientists who traveled to exotic locales and extracted ancient treasure from rocks, were complete strangers. With almost nothing in common, we never met, let alone dated. We were trained differently, usually worked in entirely different university departments, and published in different scientific journals.
All of this has changed.
Now paleontologists talk of Hox genes and molecular biologists even dare use words like “Cambrian” in a sentence!
In the second part of this book, I will tell the very happy story of the union of embryology with evolutionary biology in solving the mysteries of the evolution of animal forms. The trigger for this union was, in large part, the powerful technologies of molecular biology that have provided entirely new means of looking at animal development and history. Knowledge of living animal genomes and the development of embryos allows us to look at animal history as depicted in the fossil record with a new perspective, and to make new insights into not just what happened but how—to perceive the inner workings of the making of animal diversity. One of the founding tenets of modern geology was that “the present is the key to the past”—the idea that processes we can observe now operated in and explain the past. This basic idea is also one of the fundamental principles of the new science of Evo Devo.
The first part of this book has set the stage by illustrating four critical ideas about animal development—the modularity of animal architecture, the genetic tool kit for building animals, the geography of the embryo, and the genetic switches that determine the coordinates of tool kit gene action in the embryo.
In the second half of the book, the central idea is that animal forms evolve through changes in embryo geography. We will learn the specifics of how geography and form evolve by changing the way the tool kit genes are used. Evolution of form is very much a matter of teaching very old genes new tricks!
In the course of the next chapters, we will learn about the power of Evo Devo to peer into the distant past to help us draw pictures of long extinct animal ancestors and to shed light on some of the most dramatic episodes in animal history. We will examine evolution from the deepest roots of the animal kingdom, which first emerged in ancient seas more than 500 million years ago, to the origins of new structures that allowed new types of animals to make a living on the land and in the air, to the most recent twigs on the animal tree that make up the spectacular diversity of today’s animals. This builds the framework for the exploration of how we humans evolved from a small-brained, quadripedal hominid ancestor.
The stories I will tell create a vivid new picture of the evolutionary process. The impact of Evo Devo comes from both its novelty and the unprecedented quality of evidence it provides. Some of this new evidence conclusively settles long-running debates in evolutionary biology, some raises entirely new ideas, while other discoveries have revealed one of the “Holy Grails” of evolutionary biology—the precise genetic changes responsible for evolution in particular species.
Because embryology, through Evo Devo, now holds a costarring role in a fully integrated evolutionary synthesis, it is also time to change the textbooks to reflect this revolution. Indeed, I believe that Evo Devo’s methods of illustrating how animal forms evolve offers a much more powerful explanatory vision than the abstract extrapolations of the era of the Modern Synthesis. To the classic evolutionary tales of natural selection in Galapagos finches and peppered moths, Evo Devo now adds deep insights from lobsters and shrimp, spiders and snakes, spotted butterflies, pocket mice, and jaguars. And it illustrates as never before how Darwin’s “endless forms” have been and are being made.
Olenoides serratus trilobites of the Burgess Shale. PHOTO BY CHIP CLARK, BY PERMISSION OF SMITHSONIAN INSTITUTION