INTRODUCTION 17 



extinct Land-dragons, or Dinosaurs, has been by no 

 means universally accepted. Some authorities like Dr. A. 

 Smith Woodward and Professor Osborne interpret these 

 after another fashion. They hold that these are the 

 " expression points " of inherent growth forces, a 

 process of concentration marking the final stages of 

 evolution prior to extinction. From which it may be 

 inferred that there is a term to the life of a species as 

 there is to the life of the individual. In many cases 

 it is suggested the very exuberance of growth has been 

 the exterminating factor, as in the case of the huge 

 antlers of the Irish " elk," whose enormous weapons 

 hampered his endeavours to escape his enemies. This 

 is the theory of " Orthogenesis," or direct development. 

 According to this, new structures, arising in the germ- 

 plasm as " variations," will of their own inherent vitality 

 go on increasing in each generation unless, and until, 

 checked by " Natural Selection." Changes in the 

 character of the " Hormones " might very well bring 

 about these excesses of growth. It is well known that 

 the exuberance of growth which produces giants 

 among the human race is due to a derangement of the 

 secretions or hormones of the pituitary body which 

 largely control growth. 



Another factor of Sexual Selection which is commonly 

 ignored, but which is of profound importance, is to be 

 found in the part played by the emotions in regard to 

 sexual relationships ; the part which the " mind " has 

 played, and plays, in the mating of animals, at any rate 

 of the higher types. 



Darwin touched but lightly on this theme. Later 

 writers have almost entirely ignored it. Almost all that 

 is worth knowing on the subject we owe to Professor 



2 



