STERILITY 11 



be contaminated with a cross of another race, and 

 agriculturists know how difficult they find always to 

 prevent this, effect would be trueness. This char- 

 acter and sterility when crossed, and generally a 

 greater amount of difference, are two main features, 

 which distinguish domestic races from species. 



[Sterility not universal admitted by all 1 . 

 Gladiolus, Crinwn, Calceolaria* must be species if 

 there be such a thing. Races of dogs and oxen: but 

 certainly very general ; indeed a gradation of sterility 

 most perfect 3 very general. Some nearest species will 

 not cross (crocus, some heath (?)), some genera cross 

 readily (fowls 4 and grouse, peacock &c.). Hybrids 

 no ways monstrous quite perfect except secretions 5 

 hence even the mule has bred, character of sterility, 

 especially a few years ago (?) thought very much 

 more universal than it now is, has been thought the 

 distinguishing character; indeed it is obvious if all 

 forms freely crossed, nature would be a chaos. 

 But the very gradation of the character, even if it 

 always existed in some degree which it does not, 

 renders it impossible as marks (?) those (?) suppose 

 distinct as species 6 ]. Will analogy throw any light 



1 The meaning is "That sterility is not universal is admitted by all." 



2 See Far. under Dom., Ed. 2, i. p. 388, where the garden forms of 

 Gladiolus and Calceolaria are said to be derived from crosses between 

 distinct species. Herbert's hybrid Crinums are discussed in the Origin, 

 Ed. i. p. 250, vi. p. 370. It is well known that the author believed in a 

 multiple origin of domestic dogs. 



3 The argument from gradation in sterility is given in the Origin, Ed. i. 

 pp. 248, 255, vi. pp. 368, 375. In the Origin, I have not come across the 

 cases mentioned, viz. crocus, heath, or grouse and fowl or peacock. For 

 sterility between closely allied species, see Origin, Ed. i. p. 257, vi. p. 377. 

 In the present essay the author does not distinguish between fertility 

 between species and the fertility of the hybrid offspring, a point on which 

 he insists in the Origin, Ed. i. p. 245, vi. p. 365. 



4 Ackermann (Ber. d. Vereins f. Naturkunde zu Kassel, 1898, p. 23) 

 quotes from Gloger that a cross has been effected between a domestic hen 

 and a Tetrao tetrix ; the offspring died when three days old. 



5 No doubt the sexual cells are meant. I do not know on what evidence 

 it is stated that the mule has bred. 



6 The sentence is all but illegible. I think that the author refers to 

 forms usually ranked as varieties having been marked as species when it was 



