THEORETICAL BIOLOGY 459 



minated all life; then a new period began, and an entirely new- 

 set of animals and plants was created. There was, however, no 

 evidence, either geological or theological, for any such cataclysms 

 with attendant repetitions of creation, and geologists succeeded 

 in showing that the forces which affected the form and structure 

 of the earth in the past acted in much the same way that they do 

 to-day. Thus there was gradually forced on the minds of many 

 scientists the conviction that there must have been some real 

 connection between the various types of organisms living in 

 different ages, that the later animals and plants must represent 

 the descendants of the earlier, from which they have been 

 evolved as it were. 



This theory of descent naturally met with strong opposition, 

 and one of the first questions to be asked by its opponents was, 

 How can so great variation from the original or primitive types 

 have arisen ? The French scientist, Lamarck, was one of the 

 first to answer this question; in 1809 he published his theory 

 that changes in animal species have been brought about through 

 differences in the conditions under which animals live, in other 

 words, through their environment, more especially as such differ- 

 ences involve the greater use or disuse of certain organs. Thus 

 an organ would be increased or diminished in size, and this 

 increase or diminution would be handed on to the offspring, 

 which would inherit the characteristics of the parents and if 

 living under the same conditions would accentuate them ; thus 

 in course of many generations there would be an accumulation 

 of differences, which would result in a type of structure very 

 different from the original stock. To give some concrete ex- 

 amples of how various structures would develop or disappear 

 in accordance with this theory : the hoofs of such animals as 

 the Ungulata would develop from numerous generations running 

 on hard ground ; the neck of the giraffe would lengthen from con- 

 tinually reaching after the shoots on the tree tops ; the posterior 

 appendages in the whales would be lost through the develop- 

 ment of the tail fin and their consequent disuse ; cave animals 

 would become blind through the lack of use of their eyes. 



That many organs in the body increase or diminish in size by 

 use or disuse is a fact known to all; muscular development 

 is a familiar example, but it will be noticed that Lamarck's 



