FT. I, CH. IX] OBJECTIONS TO THE HYPOTHESIS 85 



species to its nearest relative, (10) that a species may owe its 

 wide range to being part of a wide-ranging association of plants, 

 (11) that a species that occurs in a greater number of associations 

 must have taken longer to spread than one that only occurs in 

 one, (12) that climate produces great effects upon the distribu- 

 tion of a species, (13) that altitude does the same, (14) that 

 latitude also does the same, (15) that of two species with equal 

 latitudinal range the one with the greater altitudinal range will 

 be the older, and so on. 



It has, I hope, been made clear above that the distribution of 

 any one species depends upon very many factors — method of 

 dispersal, acclimatisation, suitability to the society of plants in 

 which it may find itself, local adaptation, barriers of all kinds, 

 whether physical, climatic or ecological, individual habit of the 

 species itself, and so on, as well as upon mere age. With so many 

 factors active, it is clear that probably in no single case does 

 age alone determine the area upon which a species occurs. In 

 exactly the same way, when a baby is born, it is very rarely 

 possible to say of what complaint that baby will ultimately die, 

 yet if one take a large number of babies, living in the same coun- 

 try, one can say that just so many will be accidentally killed, so 

 man^^ will die of tuberculosis, and so on. In India one can say 

 that just about so many deaths from snake-bite will occur in 

 a year; and there are many other similar cases of reasoning upon 

 large numbers, where in the large figure and the long run the 

 result is certain, yet cannot be predicted for the individual. 

 And the same is the case for Age and Area, and such objections 

 as just quoted have really no bearing upon its validity or other- 

 Av^ise. 



AVhen one takes groups of ten allies, and compares them with 

 other related groups of ten alhes, for instance, ten Mimosas with 

 ten Ingas — nearly related genera in the same family, living under 

 much the same conditions — the effects of age will show clearly, 

 because all the other factors in dispersal will either be pulling 

 the same way upon all, or will cancel one another out by pulling 

 in different directions. Ten herbaceous Compositae may occupy 

 an area X, and ten woody Dipterocarpaceae may occupy the 

 same area X, but the two are not comparable. In the former 

 case, the herbaceous habit implies many more generations in a 

 given time, and therefore many more opportunities of dispersal; 

 the parachute mechanism of the seed-dispersal enables it to 

 travel better; the fact that herbs of this kind grow in the open 



