Growth and Differentiation

The convergent trend in biological sciences already apparent in the past few years recently became more pronounced. Fields which used to be the privileged property of a restricted group are now claimed by students of different disciplines. As a consequence, in 1961, the embryo no longer belongs to the embryologist nor the microbe to the microbiologist. Barely had the fences between different biological sciences been removed when new concepts developed and old concepts appeared in a new light. Possibly no concepts profited more from this invasive trend than the old concepts of growth and differentiation. Only a few decades ago, these words conveyed mainly the idea of the developing embryo and of the laborious and intricate processes which mold it into a complete and self-supporting organism. Today, many of the biologists preoccupied with these concepts are not familiar with the embryo and, for that matter, would not be able to identify one if they were confronted with it. At present the words “growth and differentiation” have acquired such a broad significance as to encompass almost all biological sciences. Faced with the problem of delimiting the field to be discussed, the reviewers found their assignment difficult. Although one of the two would label herself an embryologist, the embryo did not benefit from her admittedly modest and one-sided knowledge of this object, not so much because of awe or the fear of not doing it justice, as because of persuasion that the embryo, as a whole, has contributed less in recent years to our understanding of growth and differentiation than simpler objects such as isolated cells or cell groups.

Our presentation is divided into two parts. In the first, we review some of the work in the field of primitive organisms, isolated cells, and cell populations, and we discuss recent advances in the field of embryonic induction. In the second, the chemical aspects of growth and differentiation are presented.