ON THE TENDENCY OF VAEIETIES, ETC. 27 



prejudiced belief in the stability of species. Equally 

 general, however, is the belief in what are called 

 " permanent or true varieties," races of animals 

 which continually propagate their like, but which 

 differ so slightly (although constantly) from some 

 other race, that the one is considered to be a variety 

 of the other. Which is the variety and which the 

 original species, there is generally no means of de- 

 termining, except in those rare cases in which the 

 one race has been known to produce an offspring 

 unlike itself and resembling the other. This, how- 

 ever, would seem quite incompatible with the " per- 

 manent invariability of species," but the difficulty is 

 overcome by assuming that such varieties have strict 

 limits, and can never again vary further from the 

 original type, although they may return to it, which, 

 from the analogy of the domesticated animals, is 

 considered to be highly probable, if not certainly 

 proved. 



It will be observed that this argument rests en- 

 tirely on the assumption, that varieties occurring in 

 a state of nature are in all respects analogous to or 

 even identical with those of domestic animals, and 

 are governed by the same laws as regards their per- 

 manence or further variation. But it is the object 

 of the present paper to show that this assumption is 

 altogether false, that there is a general principle in 

 nature which will cause many varieties to survive 

 the parent species, and to give rise to successive 

 variations departing further and further from the 



