294 EVOLUTION AND MANKIND. 



the pituitary body on the under surface of the brain. These giant 

 animals may also have been exterminated by great outbreaks of 

 parasitic diseases, such as have occurred in our own times through 

 rinderpest in cattle. 



So much for the evidences for evolution. We may now 

 briefly consider some of the hypotheses put forward to account 

 for the doctrine of descent. 



Some Hvi'otheses Regarding Evolution. 



Among some of the Greek philosophers, Nature was con- 

 sidered to have developed, and still to be undergoing a process 

 of change. Aristotle, who was the founder of comparative 

 anatomy, recognised the unity of plan prevailing throughout each 

 of the great groups of animals. Biology made little progress 

 during the Middle Ages, and it was not until the i8th century 

 that a glimmering idea of evolution, or the doctrine of descent, 

 came into being. Buifon ( 1707-1788) and Erasmus Darwin 

 (1731-1802), the grandfather of Charles Darwin, clearly stated 

 that species had not been created independently, but had origin- 

 ated from pre-existing species. However, the greatest of the pre- 

 Darwinian evolutionists was Lamarck (1744-1819), and Haeckcl 

 describes his " Philosophic zoologique " (1809) as " the first con- 

 nected and thoroughly logical ex]x>sition of the theory of 

 descent." 



When considering the various hypotheses regarding evolu- 

 tion, we must first state there are three aspects of life, the 

 organism, its (function, and its environment. The vitalists take 

 the living organism as a creative agent to be the fundamental fact. 

 In recent times, this view has been expounded by Professor 

 Bergso!!. Other naturalists have laid stress on function. Such 

 were the central ideas of Lamarck and of Erasmus Darwin. To 

 others, such as Bufifon, environment was the potent factor. 

 Charles Darwin laid stress on all three aspects of life, and 

 embodied his ideas in the hypothesis of Natural Selection. 



Evolution implies (a) raw materials in the form of varia- 

 tions*; (b) an arrangement ior securing the inheritance of some 

 of these; and {c) a directive mechanism for securing consistency 

 and effectiveness of racial change. 



A very brief outline of the views of the chief exponents of 

 evolution only can be given here. 



The main hypothesis of the famous French biologist, Lam- 

 arck, was the cumulative transmission of functional modifications. 

 For example, the long neck of the giraffe was supposed to have 

 been gradually <-Jeveloped in response to the need of the animal 

 to browse on the leaves of trees, and of constant effort in order 

 to reach such foliage. As a result, not only did the neck become 

 long, but the forelimbs also became longer than the hind limbs. 



* This statement is of fundamental importance. The existence of 



variations is an observed fact, for individuals of the same parentage are 

 not identical. 



