EVOLUTION 359 



Environment : Use and Disuse. — The early views of the guiding fac- 

 tors involved almost exclusively the environment and the effects of use 

 and disuse. Both of these were embodied in Lamarck's theory of evo- 

 lution. In some manner the environment was believed to be able to 

 direct the changes, from generation to generation, in certain channels. 

 Lamarck speaks of the "needs" of the animal, or even of its "desire," 

 becoming so great that the body responded by modifications in the re- 

 quired direction. Such a conception now seems to us, of course, the 

 lightest of fancies. In similar manner the effects of use and disuse were 

 believed by Lamarck to be inherited, and so to bring about modifications 

 of the species. The stretching of the giraffe's neck after branches of 

 trees, and the excessive use of the kangaroo's legs for jumping, he thought, 

 caused an over-development which was transmitted to their offspring. 

 Although the increase in length of these organs was presumably small in 

 any one individual, the accumulated increments amounted in time, 

 Lamarck beUeved, to an enormous change. These views have been 

 largelj^ abandoned by the pure biologists, who reahze that a blacksmith's 

 children, if they are stronger than other children, are so because their 

 father was inherently strong, and not because his occupation made him 

 stronger. The strength of the blacksmith, which was his by inheritance, 

 not trade, enabled him both to beget strong children and to follow a voca- 

 tion requiring brawn. However, as stated in the first chapter, there are 

 those, biologists among them, who still adhere to the Lamarckian view 

 of the effects of use. 



Natural Selection : Sexual Selection. — Darwin rejected, in the main, 

 the Lamarckian principles, and proposed in their stead several forms of 

 selection. The best known and the most generally applicable of his 

 theories is that of Natural Selection which, indeed, is often called by the 

 name Darwinism. Animals, he said, naturally varied among themselves. 

 If the variation of certain individuals was such as to give them a better 

 chance in the struggle for existence, those individuals would survive in 

 larger numbers than their less fortunate fellows, or would hve longer and 

 produce more offspring. Darwin assumed that, on the whole, the varia- 

 tions which helped these individuals would be transmitted to their progeny. 

 In the next generation, he thought, the selection in favor of this variation 

 would be repeated. In time, by this natural selection, a new race would 

 be estabhshed. To explain such useless features as the gorgeous plumage 

 of some kinds of male birds, features that could not help in the ordinary 

 struggle for existence, Darwin postulated sexual selection. The more 

 brilhant males, he thought, were more successful in courtship, and so 

 left more progeny. Assuming variations in coloration to be inherited, a 

 race having highly colored males would thus be evolved. In the hands 

 of Darwin's followers and admirers the idea of selection was developed to 

 an extraordinary degree. The most insignificant features were held to 



