How Does Nature Work?
The third, and arguably most open-ended, type of scientific question seeks to understand the processes by which nature works: how stars evolve, how rocks erode, how cancer develops, how atoms interact, how fungi reproduce-on and on, questions that arise by the millions. Descriptions of the dynamic evolution and interplay of natural systems help us not only understand the past and present but also predict the future of our physical surroundings. Perhaps of more immediate interest, knowledge of how nature works will help us address problems of fundamental importance to our well being. In fact, most of today’s basic scientific research focuses on answering such questions, and the findings are revealing bewildering complexity.Consider one of the oldest mysteries of science: how a single fertilized egg transforms into a human being. As an embryo develops, cells must adopt exact spatial relations in a precise time-ordered pattern. As the first cell divides again and again, head, gut, legs, and heart assume their unique identities while new generations of cells play the specialized roles of blood, bone, and brain.
How is it possible for the genes in a solitary fertilized egg to contain all the information necessary to produce a complex individual? This question, first explored a century ago by German biologist Wilhelm Roux in microscopic studies of frog embryos, has blossomed into one of the most exciting frontiers of science, engaging thousands of researchers and showing no sign that a complete answer will ever be forthcoming.
Moreover, it’s hard to imagine a scientific question that will have a more complex and lengthy answer. Documenting and describing the countless individual steps that yield a single fly-the rough bristles of its legs, the regimented facets of its eye, the exquisite tracery of its wings-will require thousands of thick volumes, each richly illustrated and dense in the jargon of genetics. For a human being, the volumes might number in the millions, and we are still a long way from knowing what to put in such books.
It may take centuries to learn many crucial details of the developmental processes that sculpt our faces, our bodies, and our minds, but a few underlying principles are beginning to emerge through remarkable laboratory experiments. This science, known as developmental biology, often seems peculiar to casual observers since it focuses largely on what goes wrong rather than what goes right. That’s because it’s almost impossible to track the genetic pathways of development when everything goes according to plan. Even if we could freeze the sequence of events and examine every embryonic cell at every step along the way, too many processes occur simultaneously and too many genes play a role. What’s more, humans develop much too slowly-and the ethics of embryo research are too touchy-to make much progress studying our own species.
Developmental biologists, hoping to learn how humans develop normally, therefore concentrate their efforts on much simpler fast-breeding organisms that develop abnormally. The standard research strategy involves growing countless millions of short-lived animals, most often the fruit fly Drosophila melanogaster, with its convenient 10-to-14-day life cycle. Thousands of scientists spend their entire research lives working on the genetics and development of the fly, the most thoroughly studied of all complex organisms. (A simple species of flat worm, Caenorhabditis elegans, comes in a distant second, followed by small vertebrates such as zebrafish, frogs, and mice.)