THE EVOLUTION OF ANIMAL LIFE 



enemies, it follows that each generation has been forced to exert itself to 

 the utmost, like an athlete always in training for a race, and that the effects 

 of such training in each generation have been passed on to the next. Thus, 

 fleetness has gradually increased up to limits determined by the nature of the 

 organism. Similarly, the fleetness of the pursuing wolves may have been 

 increased generation after generation. Animals living in cold climates, where 

 the environment stimulates a heavier growth of hair or the formation of more 

 fat beneath the skin, are believed to transmit these characters by heredity; 

 their descendants at length reach the state seen in arctic forms. Many other 

 examples of this line of reasoning could be cited, such as the degeneration of 

 the eyes in cave-dwelling animals, the increase in neck length in giraffes, 

 and so on. Lamarck also believed that the animal in some way "willed" or 

 determined the course of its evolution. 



Present Status and Critique. If it could be shown that the effects of use 

 and disuse and the direct effects of environment upon the individual are 

 actually inherited, there would be little criticism of Lamarck's theory. 

 Many attempts have been made to obtain specific evidence, but none of the 

 alleged examples has held up under subsequent investigation. Experiments 

 involving the destruction of parts, such as the amputation of tails in mice 

 during many generations, and experiments in the functional stimulation of 

 various parts, and in the effects of changed environment, have given negative 

 results. The organism may develop new characters in a new environment, 

 but when it is returned to the original environment, the alterations do not 

 persist. In general, it may be said that experimentation has failed to sup- 

 port the Lamarckian theory; it appears that characters acquired by the 

 individual during its lifetime, in the manner postulated by Lamarck, are 

 not heritable. 



A theoretical objection may be raised to the entire idea of the inheritance 

 of such acquired characters. A new individual develops not from its parents' 

 somatic cells but from their germ cells; and germ cells are in most cases set 

 apart at an early stage in development and are little influenced by what hap- 

 pens to the somatic cells in the normal activities of the animal. The Lamarckian 

 scheme would require that a change in somatic cells of a part of the body be 

 transmitted to the germ cells, in such a way as to affect whatever it is in the 

 germinal material that conditions the development of this specific part. To 

 use a homely if old-fashioned illustration, a blacksmith's son inherits his 

 arms not from his father's arms but through his father's and mother's germ 

 cells; and it is the germ cells that must be changed before any modification 

 can be inherited. The facts of genetics, embryology, and physiology give 

 virtually no theoretical support to the Lamarckian doctrines and thus con- 

 firm the negative results of experimentation. 



Darwin's Theory of Natural Selection: Historical. The teachings 

 of Lamarck regarding evolution attained considerable popularity during 

 the early nineteenth century but were apparently overthrown by Cuvier 

 (1769-1832), the greatest zoologist of his day, who opposed the concept 



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