ARE SPECIFIC CHARACTERS ALWAYS USEFUL? 255 
ciple when he attributes the disappearance of ‘‘rudimentary organs” 
to the action of ‘‘panmixia.’’ Now, in the cessation of reflexive selec- 
tion which follows independent breeding, a similar principle is intro- 
duced, and the inevitable result must be the weakening of the power 
of heredity by which the portions of the species were held in corre- 
spondence with each other before their separation. I have elsewhere 
shown that separate breeding necessarily disturbs unstable adjust- 
ments; and we here see that the most stable of the adjustments by 
which each part of a species is kept in correspondence with every 
other part gradually becomes unstable under the continued influence 
of separation. Whenever a species is divided into two portions that 
do not interbreed, the forms of reflexive selection will cease to act 
between the two portions, and they will continue in sexual, social, 
and other forms of harmony with each other only in so far as the 
force of the old heredity holds them to the old standards. But the 
power of heredity in these respects will in time fail, and if the sep- 
arate breeding is long continued, incompatibility in all these respects 
tends gradually to arise. Moreover, it is manifest that incompatibil- 
ity of industrial habits involving diversity in the forms of active (or 
endonomic) selection will in time arise. I therefore maintain that 
separation, which necessarily includes cessation of reflexive selection 
between the portions separated, is a cause of segregation and diver- 
gence; and that this segregation is in time intensified by diversity of 
environal selection, through diversity in the use of the environment. 
Unless the separated portions of a species possess exactly the same 
average character (which we must believe is seldom, if ever, the case), 
separation must, from the first, be more or less segregative; and even 
in cases where the portions completely correspond in character (if 
there are any such cases), the cessation of reflexive selection which 1s 
involved in the separate breeding must result in divergence as soon as the 
power of heredity securing the original adjustments begins to weaken; and 
this is in due time followed by other forms of intensive segregation. 1 
therefore conclude that indiscriminate separation may be regarded as 
a preliminary form of segregation (that is, as demarcational segrega- 
tion) and that intensive segregation codperating with this produces 
complete segregation. 
IV. THe UTriLity oF SPECIFIC CHARACTERS.* 
I have followed the discussion on the utility of specific characters 
with great interest; and though I am at such a distance that my 
thoughts may come a little late, I wish to call attention to a few points. 
* Published in Nature, April 1, 1897. 
