Evolutionary Theory and Zoological Practice
In surrendering to Washington at Yorktown, Cornwallis' band played a ditty about the "world turned upside down." A reassembly of the chorus in 1859 would not have been inappropriate. Darwin's youthful essays of 1842 and 1844 record what must be the greatest of all intellectual delights: the systematic reconstruction of a body of knowledge according to novel principles of one's own invention. Intellectual historians have emphasized the profound impact of evolutionary theory upon social and political life; yet it is ironic that biologists often incorporated the new explanations without substantially altering their scientific practice. Systematists, for example, could easily explain homology by common evolutionary descent rather than similarity of divine thought; yet the procedures for recognizing homologies and constructing classifications from them were little disturbed by this explanatory reversal.1 Alpheus Hyatt noted (with some surprise in hindsight) that he had been able to transfer bodily to evolutionary theory the taxonomic conclusions that Agassiz had based upon the creationist interpretation of recapitulation: "Although within a year after the beginning of my life as a student under Louis Agassiz I had become an evolutionist, this theoretical change of position altered in no essential way the conceptions I had at first received from him, nor the use we both made of them in classifying and arranging forms" (1897, p. 216).
The epigenetic character of embryology made it a field for phyletic speculation that no evolutionist could resist. There existed, in 1859,