348 EVOLUTION, GENETICS, AND EUGENICS 



and theories. The facts are there for us to explain, and the theories 

 are attracting so much attention at present that they should not be 

 ignored. 



Increase in size is one of the commonest trends of evolution; but 

 is size increase progress? Many great groups of organisms have from 

 age to age steadily increased in size of individuals. Many fossil pedi- 

 grees show clearly that size increase is one of the steadiest of progres- 

 sive trends. But size, if carried to extremes, is disadvantageous; wit- 

 ness the complete extinction of the ancient dinosaurs and the rapidly 

 progressing extinction of the whales and elephants today. 



Increase in intelligence is claimed to be one of the signs of progress in 

 evolution. In vertebrates, especially, there is a progressive series of 

 forms showing greater and greater intelligence, ranging from fishes to 

 man. Accompanying and underlying this increase in intelligence, 

 there has gone on in vertebrates a steady increase in the size, specializa- 

 tion, and compactness of the brain and its associated sense organs. 

 This steady trend is commonly spoken of by students of vertebrates as 

 cephalization. Is the final goal of evolution then the production of 

 more and more intelligent organisms? If that were true, why should 

 so much evolution be going on that seems to be moving in the opposite 

 direction, resulting in the decephalization of many sedentary organisms 

 and parasites? 



You see it is difficult to discover any general or universal goal of 

 evolution. We do not even agree as to the direction of evolution, so 

 we cannot be sure what is progress and what is regress. Under these 

 circumstances, it may seem, at first thought, rather futile to discuss 

 guiding factors at all. Most of us, however, retain the firm conviction 

 that evolutionary change has in it something of direction, something of 

 fitness, and something of progress, though we may not always be able 

 to demonstrate direction or fitness or progress in particular cases. 



Evolutionists, however, have always assumed that evolution is 

 progressive, that adaptation is a reality, and that there have been 

 definite evolutionary trends. Believing in these phenomena, they 

 have tried to explain them. The two classic attempts to explain pro- 

 gressive evolution are Darwin's theory of natural selection and La- 

 marck's theory of the inheritance of acquired characters. These 

 theories are to be critically discussed in chapters xxx and xxxi respec- 

 tively. 



