LAWS OF VARIATION 127 



long- continued descent. It is notorious that each 

 species is adapted to the climate of its own home : 

 species from an arctic or even from a temperate region 

 cannot endure a tropical climate, or conversely. So 

 again, many succulent plants cannot endure a damp 

 climate. But the degree of adaptation of species to 

 the climates under which they live is often overrated. 

 We may infer this from our frequent inability to pre- 

 dict whether or not an imported plant will endure our 

 climate, and from the number of plants and animals 

 brought from warmer countries which here enjoy good 

 health. We have reason to believe that species in a 

 state of nature are limited in their ranges by the com- 

 petition of other organic beings quite as much as, or 

 more than, by adaptation to particular climates. But 

 whether or not the adaptation be generally very close, 

 we have evidence, in the case of some few plants, of 

 their becoming, to a certain extent, naturally habitu- 

 ated to different temperatures, or becoming acclima- 

 tised : thus the pines and rhododendrons, raised from 

 seed collected by Dr. Hooker from trees growing at 

 different heights on the Himalaya, were found in this 

 country to possess different constitutional powers of 

 resisting cold. Mr. Thwaites informs me that he has 

 observed similar facts in Ceylon, and analogous obser- 

 vations have been made by Mr. H. C. Watson on 

 European species of plants brought from the Azores 

 to England. In regard to animals, several authentic 

 cases could be given of species within historical times 

 having largely extended their range from warmer to 

 cooler latitudes, and conversely ; but we do not posi- 

 tively know that these animals were strictly adapted 

 to their native climate, but in all ordinary cases we 

 assume such to be the case ; nor do we know that they 

 have subsequently become acclimatised to their new 

 homes. 



As I believe that our domestic animals were origin- 

 ally chosen by uncivilised man because they were 

 useful and bred readily under confinement, and not 

 because they were subsequently found capable of far- 



