4 The Expansion of Evolutionary Concepts 



synthesis of genetics and evolutionary theory had been achieved 

 by notable investigators such as Theodosius Dobzhansky, Ernst 

 Mayr, C. Darlington, and G. G. Simpson. By this time, A. E. Emerson 

 had made the first serious efforts to extend evolutionary principles 

 to multiple-species systems. 



Geological studies after Darwin provided and continue to provide 

 examples of what did happen in the evolution of many plant and 

 animal groups. This mass of data has provided material of great 

 interest relating to the actual products of evolution, including rates 

 of change and patterns of dispersal, survival, and extinction. 



In recent years, biochemistry has added a new dimension both 

 to genetics and evolution. New insights into the chemistry of life 

 have contributed valuable clues concerning the origin of life and 

 what the first life might have been like, as well as the nature of 

 the genetic material which carries the biochemical information that 

 is heredity itself. Future discoveries in this area are sure to have 

 a profound effect on many present ideas of inheritance and muta- 

 tion. 



It might seem that by now, over a hundred years after the an- 

 nouncement of the historic Darwin-Wallace theory, the process of 

 evolution should be well understood. For its general outlines, this 

 is true, but the advances made in these hundred years have served 

 also to underscore deeper and little-explored facets which the ad- 

 vances have brought to light. There is today controversy on many 

 points of evolutionary theory. 



Difficulties in investigating the evolution of life and the con- 

 troversies concerning its explanation stem in large part from two 

 simple facts. First, the living world had evolved from non-living 

 matter to the vast complexity of life as we know it before man and 

 his historical pen had evolved. As a result, we have no choice but 

 to attempt an explanation of past happenings on the basis of existing 

 data. This hypothetical reasoning has definite philosophical limita- 

 tions that frequently invite multiple explanations (hence contro- 

 versy ) and always requires the checking and rechecking of hypoth- 

 eses in the light of new data or new perspectives. In the interpreta- 

 tion of fossils, for example, at least two sets of hypotheses are 

 always involved. Fossils are not found bearing labels stating their 

 identity; the strata in which they are found are likewise unlabelled. 

 Both unknowns must be solved by comparatixe anatomy, compara- 

 tive lithology, relative position in the geologic column, and other 

 means, all of them based in turn on hypotheses or theories of 

 homology or stratigraphy. Because of the necessity for reliance on 



