Evolution of embryology: a synthesis of classical, experimental, and molecular perspectives.

Embryology as a modern science began at the beginning of the 19th century and continued as the classic period until the 1940s. During this period, a body of basic knowledge was established which, generally, described the events of development. From 1940 to 1970 experimental or causal embryology predominated; explanations of secondary causes were demonstrated for development. The decade of the 1970s was a decade of transition that led to the current revolution in molecular biology that began in the 1980s. Molecular biology and its new branch, molecular genetics, shook up the heretofore serene, but already limited, field of embryology. Today the discipline of embryology is being built on the analysis of the results of genetic expression. Embryology is now concerned with understanding development from the viewpoint of the activation and transcription of DNA sequences, which will allow us to approach the first causes or underlying genetic and epigenetic mechanisms of development. As a result, embryology and genetics have fused into a wider biological subdiscipline, developmental biology. Will this be enough to define the full scope of our knowledge of embryonic development? What is certainly evident is that the molecular period of embryology will help achieve a better understanding of the schemata constructed by classic and experimental embryologists. Furthermore, to the degree that the molecular analysis of whatever phenomenon of development requires additional foundational knowledge, classic and experimental embryology will not have exhausted all their possibilities.