PLANT EVOLUTION 239 



Darwin. This well-known English scientist (Fig. 108) ad- 

 vanced the theory of Natural Selection in 1859 in his book en- 

 titled The Origin of Species. He assumed that creation was a 

 continuous evolutionary process and that the most important 

 factor was natural selection. This theory was based on the idea 

 that every individual plant and animal must be fitted to its 

 environment and that it is in competition with other plants 

 and animals. Very naturally those individuals that were best 

 suited to their environment and able to compete with their 

 rivals and enemies of various kinds would 

 survive and produce offspring, while those 

 that were not so favored by nature would 

 perish, leaving few or no progeny. This 

 theory involved variation, inheritance, 

 struggle for existence and survival of 

 the fittest. 



Individual variation is very generally 

 recognized by all close observers of nature. 

 Xo two individuals are exactly alike, 



. . FIG. 108. Charles Darwin. 



although it may be very difficult t^ point 



out the differences. In fact, the leaves (Fig. 109) on the plant 

 show more or less decided variations. Darwin believed that when 

 these individual variations proved advantageous, the possessor 

 would have more chance of surviving and producing offspring 

 than the individual that did not .possess them. He also believed 

 that valuable variations were transmitted (or inherited) and 

 intensified from generation to generation. Therefore, these 

 gradual variations would eventually give rise to a race or species 

 of individuals quite different from their ancestors. 



Darwin's ideas involved the struggle for existence and the 



