3 There are other trends in the attempt to meld evolution and
development which immodesty permits me to add. I have been concerned
over the years with the selection forces which might have produced
larger organisms and therefore a development of increasing complexity.
This is nowhere more evident than in the multiple evolutionary origins
of multicellularity and all the variety of developmental mechanics that
have gone with it. (I discuss this and related themes in various places,
but see especially The Evolution of Development (1958; (1)) and Size and
Cycle (1965; (2)). To some degree these examples of the bringing
together of evolu- tion and development are exceptions. By far the most
important historical trends in this century have been the success of in-
dividual disciplines. Embryology had its great flowering be- ginning in
the last century, coming to a climax with the work of Spemann on
induction in the first two decades of this cen- tury. Genetics has had
an extraordinary continuing series of revolutions beginning with the
rediscovery of Mendel and pro- gressing through Morgan to the flash
flood of molecular genetics and the structure of DNA. This flood was a
flash only in the sense that it rushed upon us with amazing speed; its
effects in the form of important and exciting work produced has not
subsided and we are still in a peak period of molecular genetics.