EVOLUTION, HEREDITY, EUGENICS 517 



"While within each of the major animal groups or phyla the inter- 

 relationships of the various included types as they appear in successive 

 geological horizons are such that they may be represented in the form of a 

 tree — the so-called phylogenetic tree — there is no real evidence, paleonto- 

 logical, embryological or structural, that any of the phyla were derived 

 from any of the others, although all of them must have been derived from 

 a primitive single cell. Each of the phyla represents a special and definite 

 structural complex basically different from the structural complex repre- 

 sented by any other. 



"The protozoans differ from all other groups in the complete separa- 

 tion of the cells after division. The sponges are unique in the more or 

 less irregular adhesion of the cells after division in the early embryonic 

 stages. All other groups pass through a gastrula or its equivalent, and 

 the gastrula is the last stage common to them all. 



"It is therefore assumed that, so far as the major groups of phyla 

 are concerned, evolution was a more or less simultaneous process of 

 radiation from the gastrula stage, and that the phyla never were con- 

 nected by intermediate types any more closely than they are at present. 



"This conclusion agrees with the determined facts of paleontology 

 and embryology, and furthermore accords with our interpretation of 

 conditions on the earth at and subsequent to the first appearance of life." 



Significance of the Darwinian Theory. — We owe to Darwin the 

 first successful vindication of the evolution idea. It was not his 

 own, nor was he its first champion, yet we think of Darwin and the 

 Doctrine of Descent together. The central idea of evolution is 

 that the present is the child of the past and the parent of the future. 

 It is the idea of progressive change from phase to phase without 

 loss of continuity. Crampton says, " The Origin of Species has 

 proved a veritable Magna Charta of Intellectual liberties, for as no 

 other single document before or since it has released the thoughts of 

 man from the trammels of unreason, conservatism and dogma." 



Darwin's Pangenesis Theory. — Charles Darwin is responsible 

 also for a theory of inheritance units. He supposed that each cell 

 of the body throws off little particles which he called gemmules^ 

 which are somehow gathered together in the germ cells. When these 

 develop, the gemmules reproduce in the body of the new individual 

 the characters of these cells of the parent from which they were 

 derived. With this the transmission of acquired characters is per- 

 fectly natural. The theory is called the pangenesis theory because 

 it assumes that all parental somatic cells are concerned in the for- 

 mation of the new individual. It is interesting to note that in spite 



