723 
1921 .] and their part in Evolution. 
Wheatear, Blue and White Herons (Ardea rufa )—all the 
factors will be the same except one or two ; bnt on my 
reasoning they are none the less good species, because they 
do not contain exactly the same factors. How all subspecies 
of a given 44 unit ” contain exactly the same factors ; but the 
somatic expression of these factors has been originally 
altered by the environment, and subsequently become in¬ 
herited. We have only to note in domestic types the 
reversion, after some generations, to the wild form to prove 
the truth that the factors have remained unchanged, but 
that the alterations caused by environment (domestication) 
have been so far inherited that the reversion is not complete 
for several generations.' 
Since the above was written, I have had the pleasure of 
reading Colonel Meinertzhagen^s excellent article in the 
current number of 4 The Ibis/ p. 528, to one or two points 
of which I should like to refer. 
The author is of opinion that no deductions from 
mutations carried out on domestic varieties can be of value, 
since such conditions do not exist in Nature; but surely by 
carrying out heredity experiments under conditions which 
we know, we are able the more accurately to attempt to 
understand the laws of heredity, and can then see if they 
would apply to wild species under natural conditions. 
There is, to my way of thinking, no need to question 
whether species arose by mutations or by gradual selection. 
In the case of domestic freaks, which form but a small 
proportion of domestic races, they probably originated as 
mutations; but by far the greater number of our 44 fancy'” 
breeds to-day have been brought about by a process of 
careful and minute selection in order to intensify or diminish 
any particular trait or character ; and in that process each 
generation would show a larger and increasing proportion of 
individuals having that character, thus proving that not 
only any particular character, but also its intensification, 
was inherited. The reason this fact is not fully recognized is 
because of the comparatively short periods during which a 
