No. 49.3] 



WHAT IS A SPECIES? 



193 



genetic changes. If, in the examination of abundant ma- 

 terial from different natural environments, we find these 

 characters fairly constant, the forms may properly be 

 called species ; if not, varieties or races. Xo perfect spe- 

 cific description can be drawn from a single specimen or 

 from a few even, and the skill of the taxonomist is con- 

 spicuously shown in his ability to distinguish between 

 variable and fixed characters, between the essential and 

 non-essential, in other words, between old and new char- 

 acters. Some taxonomists— and I know such— remain, 

 after many years' experience, unable to dissociate indi- 

 vidual from specific or generic characters; they describe 

 species as they would describe the physical features of a 

 tree or of a rock— and they are the ones who deserve the 

 condemnation of other workers. Are such workers con- 

 fined exclusively to our branch of biology ? 



In nature the interrelated factors, of which environ- 

 ment and heredity are the chief, are normally in a state 

 of substable equilibrium— variations within given groups 

 are within certain fairly definite limits, because the fac- 

 tors of variation are. If, however, the cumulation of any 

 one factor, either naturally or artificially, occurs, the vari- 

 ations become inconstant and the limits of variation are 

 changed. The wild pigeon in nature, for instance, is 

 governed by fairly constant conditions, and its variations 

 are small. Its domestic varieties, were they existent in 

 nature, would not interbreed, and would be good species. 

 Breeders, I think, lose sight of such things when they say, 

 as some do, that they can produce specific characters, that 

 is, characters which are deemed of specific value by tax- 

 onomists. They can do nothing of the sort. You may 

 break down by changed environments and artificial selec- 

 tion what would be real specific characters under natural 

 selection and natural environment, but you do not make 

 species thereby. Time and fixation by heredity, I believe, 

 must always be taken into account in determining varietal, 

 specific or generic characters. Mutations of (Enothera 

 lamarcMana were found growing wild by de Vries, es- 



