1864.] DR. DAWSON ON CLASSIFICATION OF ANIMALS. 245 



the progeny might be different from the parents, then the charac- 

 ters of the species would speedily become changed, and it would 

 practically cease to be the same. Again, it is necessary that the 

 reproduction of species should be pure or unmixed ; for an indis- 

 criminate hybridity would soon obliterate the boundaries of spe- 

 cies. It is impossible, therefore, to separate the idea of species 

 from the power of continuous unchanged reproduction, without 

 depriving it of its essential characters. 



In like manner it is obvious that we must assume a separate 

 origin for each species, and that we need not assume more than 

 one origin. Practically, species remain unchanged, and do not 

 originate from one another ; and if all the individuals of a species 

 were destroyed except one pair, this would, under favourable cir- 

 cumstances, be sufficient to restore the species in its original 

 abundance. 



The questions which have been riiised as to the origin of spec'es 

 by descent with indefinite variation, and as to the possible creation of 

 individuals of the same species in different places or at different 

 times, are not of a practical character, at least in zoology proper, 

 and the whole burden of proof may be thrown on those who assert 

 such views. 



We are thus brought to the definition of species, long ago pro- 

 posed by Cuvier and De Candolle, and may practically unite in 

 one species all those individuals which so resemble each other that 

 we may reasonably infer that they have descended from a common 

 ancestry. All our practical tests for the determination of species 

 resolve themselves into this general consideration. The only 

 modification of this statement on which even a Darwinian can 

 insist, is, that a sufficient time and great geological changes being 

 given, one species may possibly split into two or more ; and since 

 this is an unproved hypothesis, we may practically neglect -it, 

 except as a warning to be very sure that we do not separate as 

 distinct species any forms which may be merely varieties of a 

 single species, an error exceedingly prevalent, and which vitiates 

 not a little of our reasoning on such subjects. 



The origin of the first individuals of a species may be, and 

 probably is, a problem not within the province of natural history. 

 In the case of vital force it is the same as in the case of gravita- 

 tion and other forces. We can observe its operation and ascer- 

 tain the laws of its action, but of the force itself we know nothing. 

 It is to us merely an expression of the power and will of the 



