Embryos and Ancestors
Embryos and Ancestors
IN 1930 I published a book under the title Embryology and Evolution, in which I made an attempt to show that after rejecting the theory of recapitulation, a much better synthesis could be made of our knowledge of embryonic development and evolutionary descent, opening up new fields for observation and co-ordination of studies in embryology, genetics, and evolution. Ten years later I presented the evidence again in an expanded form under the title Embryos and Ancestors, and in 1951 I published a revised edition.
During the intervening years a great deal of new evidence has become available, and these fresh data have fitted into place in my scheme like pieces of a puzzle, for I have seen no reason to alter the plan of my former book in the slightest degree. The present book is my previous one brought up to date and enlarged.
It has been very encouraging to me to note the lively interest in these problems shown in recent years. The first necessity in biology will always be further observation and experiment; but as Professor Woodger points out, progress in thought is necessary as well. Outworn theories are not only dull in themselves, but they are actually harmful in thwarting the framing of new working hypotheses which take account of recent progress made in the various experimental branches of biology. Such an outworn theory I believe Haeckel's theory of recapitulation to be. Similarly, the germ-layer theory has ceased to cover the facts.
The present time when the theory of evolution celebrates its centenary is particularly appropriate for a critical appraisement of the relations between embryology and evolution.
I should like to acknowledge my debt to M. Jean Rostand who translated my previous book into French. Few exercises are as helpful for testing the soundness of one's deductions and conclusions as the expression of them in another language, particularly his.
I wish likewise to record my indebtedness to Sir Julian Huxley, the late Professor W. Garstang, Professor Sir Ronald Fisher, and Professor J. B. S. Haldane for their helpful criticism, and to Mr. R. B. Benson, Dr. M. Burton, Dr. L. R. Cox, Mr. R. Essex, Mr. P. Freeman, Mr. R. Freeman, Dr. I. Gordon, Dr.