] 39 °"^ every single one of them is right 



upon this method of survival, or rather of flourishing, 

 quite independently. Anthropologists have long disputed 

 whether or not the use of the same tool or instrument, say 

 the throwing stick or the bow, in widely separated parts 

 of the world must mean that there was at some time some 

 contact between the ancestors of the one ethnic group and 

 the other. But there can be no such question here. Plant 

 families have spread across vast distances and they carry 

 their hereditary characteristics with them. But they have 

 no cultural traditions which can be communicated. The 

 cactus can't teach the gourd. And when the same device 

 has been invented by different plant groups there can be 

 only one possible explanation. To any problem in chemis- 

 try or mechanics there are a limited number of possible 

 solutions. Their number is fixed by the nature of things. 

 And many, perhaps all, of that limited number of possible 

 solutions have been hit upon again and again. 



Nevertheless, there remains a harder question. Since 

 there are so often several possible solutions, why has one 

 plant or animal accepted one and another plant or animal 

 another quite different? Why, to take an example, didn't 

 the gourd become succulent above ground as so many 

 plants of so many different families did when they 

 adapted themselves to desert conditions? 



Perhaps the answer would sometimes be clear if we 

 could trace every step in the organism's history and see 

 precisely how or under what aspects the problem presented 

 itself to each plant or animal. But even so, the answer 

 would probably not always be forthcoming. Something in 

 the given nature of an individual species probably predis- 

 poses it to one solution rather than another. 



This fact is one which students of evolution and genetics 



