Chap. I.] VARIATION UNDER DOMESTICATION. 7 



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

 inflammations of various organs. 



With respect to what I have called the indirect action of changed 

 conditions, namely, through the reproductive system 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 con- 

 ditions, and partly from the similarity, as Kolreuter and others 

 have remarked, between the variability which follows from the 

 crossing of distinct species, and that which may be observed with 

 plants and animals when reared under new or unnatural conditions. 

 Many facts clearly show how eminently susceptible the reproduc- 

 tive system is to very slight changes in the surrounding conditions. 

 Nothing is more easy than to tame an animal, and few things more 

 difficult 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 display 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 

 aome 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 ; 

 but to show how singular the laws are which determine the repro- 

 duction of animals under confinement, I may mention that car- 

 nivorous animals, even from the tropics, breed in this country 

 pretty freely under confinement, with the exception of the planti- 

 grades or bear family, which seldom produce young ; whereas 

 carnivorous birds, with the rarest exceptions, hardly ever lay fertile 

 eggs. Many exotic plants have pollen utterly worthless, in the 

 same condition as in the m ost sterile hybrids. "When, on the one 

 hand, we see domesticated animals and plants, though often weak 

 and sickly, breeding freely under confinement ; and when, on the 

 other hand, we see individuals, though taken young from a state of 

 nature perfectly tamed, long-lived and healthy (of which I could 

 give numerous instances), yet having their reproductive system so 

 seriously affected by unperceived causes as to fail to act, we need 

 not be surprised at this system, when it does act under confinement, 

 acting irregularly, and producing offspring somewhat unlike their 

 parents. I may add, that as some organisms breed freely under 

 the most unnatural conditions (for instance, rabbits and ferrets kept 

 in hutches), showing that their reproductive organs are not easily 

 affected ; so will some animals and plants withstand domestication 



