ttOW rLANDS CAME TO t)IFFER. 29 



to the birds that swallow and disperse them. 

 How did this all come about ? What made the 

 adaptation ? It is a result of two great under- 

 lying principles known as The Stnigijlc for Lifc^ 

 and Natural Selection. 



Since each early plant goes on growing and 

 dividing, again and again, as fast as it can, it 

 must follow in time that a great number of 

 plants will soon be produced, each lighting with 

 the others for air and sunlight. Now, some of 

 them must, by pure accident of situation, get 

 better placed than others ; and these will pro- 

 duce greater numbers of descendants. Again, 

 unless all of them remained utterly uninfluenced 

 by circumstances (which is not likely) it must 

 necessarily happen that slight differences will 

 come to exist between them. These differences 

 of outline, or shape, or cell-wall, may happen to 

 make it easier or harder for the plant to get 

 access to carbonic acid and sunlight, or to 

 disperse its young, or to fix itself favourably. 

 Those plants, therefore, which happened to vary 

 in the right directions would most easily go on 

 living and produce most descendants, while 

 those which happened to vary in the wrong 

 directions would soonest die out and leave 

 fewest descendants. 



Well, the world around us, both of plants and 

 animals, is full of creatures all struggling against 

 one another, and all competing for food and air 

 and sunshine. Moreover, each individual pro- 

 duces (as a rule) a vast number of young ; some- 

 times, like the poppy, many thousand seeds on 

 a single flower-stem. Now suppose only ten of 



