NATUKAL SELECTION. 



scarcely a plant can be named, though cultivated in the rudest 

 manner, which has not given birth to several varieties. It can 

 hardly be maintained that' during the many changes which this 

 earth has undergone, and during the natural migrations of plants 

 from one land or island to another, tenanted by different species 

 that such plants will not often have been subjected to changes 

 in their conditions analogous to those which almost inevitably 

 cause cultivated plants to vary. No doubt man selects varying 

 individuals, sows their seeds, and again selects their varying 

 offspring. But the initial variation on which man works, and 

 without which he can do nothing, is caused by slight changes 

 in the conditions of life, which must often have occurred under 

 nature. Man, therefore, may be said to have been trying an 

 experiment on a gigantic scale ; and it is an experiment which 

 nature during the long lapse of time has incessantly tried. Hence 

 it follows that the principles of domestication are important for 

 us. ^ The main result is that organic beings thus treated have 

 varied largely, and the variations have been inherited. This 

 has apparently been one chief cause of the belief long held by 

 some few naturalists that species in a state of nature undergo 

 change. 



I shall in this volume treat, as fully as my materials permit, 

 the whole subject of variation under domestication. We may 

 thus hope to obtain some light, little though it be, on the 

 causes of variability— on the laws which govern it, such as the 

 direct action of climate and food, the effects of use and disuse, 

 and of correlation of growth,— and on the amount of change to' 

 which domesticated organisms are liable. We shall learn some- 

 thing on the laws of inheritance, on the effects of crossing dif- 

 ferent breeds, and on that sterility which often supervenes when 

 organic beings are removed from their natural conditions of life, 

 and likewise when they are too closely interbred. Durino- this 

 investigation we shall see that the principle of Selection Is all 

 important. Although man does not cause variability and cannot 

 even prevent it, he can select, preserve, and accumulate the 

 variations given to him by the hand of nature in any way 

 which he chooses; and thus he can certainly produce a 

 great result. Selection may be followed either methodically 

 and intentionally, or unconsciously and unintentionally. Man 



