VARIATION UNDER DOMESTICATION 27 



ilance from either parent or from some more remote ances- 

 tor. Even strongly-marked differences occasionally appear 

 in the young of the same litter, and in seedlings from the 

 same seed capsule. At long intervals of time, out of millions 

 of individuals reared in the same country and fed on nearly 

 the same food, deviations of structure so strongly pro- 

 nounced as to deserve to be called monstrosities arise; but 

 monstrosities cannot be separated by any distinct line from 

 slighter variations. All such changes of structure, whether 

 extremely slight or strongly marked, which appear amongst 

 many individuals living together, may be considered as the 

 indefinite effects of the conditions of life on each individual 

 organism, in nearly the same manner as the chill affects dif- 

 ferent men in an indefinite manner, according to their state 

 of body or constitution, causing coughs or colds, rheumatism, 

 or inflammation of various organs. 



With respect to what I have called the indirect action of 

 changed conditions, namely, through the reproductive sys- 

 tem of being affected, we may infer that variability is thus 

 induced, partly from the fact of this system being extremely 

 sensitive to any change in the conditions, and partly 

 from the similarity, as Kolreuter and others have re- 

 marked, between the variability which follows from the 

 crossing of distinct species, and that which may be ob- 

 served with plants and animals when reared under new 

 or unnatural conditions. Many facts clearly show how 

 eminently susceptible the reproductive system is to very 

 slight changes in the surrounding conditions. Nothing is 

 more easy than to tame an animal, and few things more diffi- 

 cult than to get it to breed freely under confinement, even 

 when the male and female unite. How many animals there 

 are which will not breed, though kept in an almost free state 

 in their native country ! This is generally, but erroneously, 

 attributed to vitiated instincts. Many cultivated plants dis- 

 play the utmost vigour, and yet rarely or never seed ! In 

 some few cases it has been discovered that a very trifling 

 change, such as a little more or less water at some particular 

 period of growth, will determine whether or not a plant will 

 produce seeds. I cannot here give the details which I have 

 collected and elsewhere published on this curious subject; 



