[{241}] In the present Essay there is some evidence that the author attributed more to sports than was afterwards the case: but the above passage points the other way. It must always be remembered that many of the minute differences, now considered small mutations, are the small variations on which Darwin conceived selection to act.
[{242}] See Var. under Dom., Ed. ii. vol. II. p. 230.
[{243}] «Note in the original.» If domestic animals are descended from several species and become fertile inter se, then one can see they gain fertility by becoming adapted to new conditions and certainly domestic animals can withstand changes of climate without loss of fertility in an astonishing manner.
[{244}] See Suchetet, L’Hybridité dans la Nature, Bruxelles, 1888, p. 67. In Var. under Dom., Ed. ii. vol. II. hybrids between the fowl and the pheasant are mentioned. I can give no information on the other cases.
[{245}] Origin, Ed. i. p. 250, vi. p. 370.
[{246}] This was the position of Gärtner and of Kölreuter: see Origin, Ed. i. pp. 246-7, vi. pp. 367-8.
[{247}] «Note in the original.» Yet this seems introductory to the case of the heaths and crocuses above mentioned. «Herbert observed that crocus does not set seed if transplanted before pollination, but that such treatment after pollination has no sterilising effect. (Var. under Dom., Ed. ii. vol. II. p. 148.) On the same page is a mention of the Ericaceæ being subject to contabescence of the anthers. For Crinum see Origin, Ed. i. p. 250: for Rhododenron and Calceolaria see p. 251.»
[{248}] «Note in original.» Animals seem more often made sterile by being taken out of their native condition than plants, and so are more sterile when crossed.
We have one broad fact that sterility in hybrids is not closely related to external difference, and these are what man alone gets by selection.
[{249}] See Var. under Dom., Ed. ii. vol. II. p. 132; for the case of the cheetah see loc cit. p. 133.