528 
Colonel R. Meinertzhagen on 
[Ibis, 
XXYII.— Some Thoughts on Subspecies and Evolution. 
By Colonel R. Meinertzhagen, D.S.O., M.B.O.U. 
In 4 The Ibis ’ of this year, p. 345, appeared a letter over 
the signatures of Dr. Lowe and Mr. Mackworth-Praed, in 
answer to a letter of Mr. Loomis in 4 The Ibis’ of 1920, 
p. 965. 
These letters bring out several points of great importance 
to those of us interested in evolution, distribution, and 
migration. These points can be enumerated as follows : — 
1. Is intergradation necessary among forms in order to 
determine their status as species or as geographical 
races ? 
2. Is a geographical race due to one cause only—environ¬ 
ment,—or can it be due to mutation ? If the latter is 
the case, should they not be species ? 
3. Are geographical races incipient species, and can 
geographical races, whose differences are obviously 
due to environment, ever develop into a species ? 
4. Of what value is the subspecies ? 
5. Definition of a subspecies. 
1. Intergradation. 
Many eminent ornithologists have accepted the fact that 
absence of intergradation among birds results in a definite 
entity, the existing species, which must remain the only 
44 definite minor unit in nature.” This is probably correct 
and covers the vast majority of geographical races, but not 
all. Insular races, which are obviously but variations due 
to isolation, having no intermediate terrain with their 
parent stock, can naturally have no intermediate or inter- 
graduating races. The same argument applies to variations 
occurring among isolated continental communities, when the 
intervening country is unsuited to the life of the species. 
In these cases isolation is as complete as insular isolation, 
and the intervening range of hills, desert, or other obstacle 
