When I studied introductory biology at the newly-coeducated Yale in the early 1970s, we didn't hear anything about stem cells. For that matter, we heard relatively little about embryos and development and much more about genetics and cell biology. The impression given was that cells are complex, they divide and multiply, and together they make up organisms. What seemed to matter most, however, were the genes, the nucleus, and to some extent the ways that genes cause the cells to act. Led by cell biologist J.P. Trinkaus, our course placed more emphasis on the interactions of cells than most courses of the time, but cell-cell interaction was not the central theme.

In biology generally, and certainly in the public mind, the "central dogma" of genetics had already taken hold and has only gained strength since. The message was that understanding biology must start with DNA, RNA, and their actions in producing proteins. Genes direct cells to develop, differentiate, and divide. Understanding development must start with the first cell, the egg cell, as it undergoes meiosis and casts off half its chromosomes in preparation for the fertilization process. Each cell division brings expression of different genes, and expression of these genes causes all the organic processes. And so it goes. Genes are inherited and they drive development; what follows is caused by heredity, or the doctrine of genetic determinism.

Or so it has seemed since DNA and genetics assumed a core place in biology in the 1960s and 1970s. What had been called embryology, or the study of embryos, became known instead as developmental biology and developmental genetics. The older emphasis on morphogenesis, differentiation, and cellular changes took a back seat to presumptions of genetic determinism as the cause of those developmental processes. My contention is that this emphasis on genetic determinism has reinforced a popular misconception that what matters about the life of an individual organism, including its form and function, is laid out fully in all relevant respects with fertilization, at the time that the full complement of chromosomes comes together from the two parents. This mistake is serious, since development actually occurs gradually, depends from the beginning on the environmental context and on cell-cell interaction to guide and inform the process, and is an epigenetic process that unfolds over time as the complex system develops.