972 
even pathological characteristics, and which 
is also commonly recognized as weakening 
vitality and vegetative strength. Thus 
many high-bred varieties of plants are 
nearly or quite seedless, while in others the 
germinating power of the seed is very low, 
facts that afford a strong indication that 
general evolutionary progress has not been 
greatly favored by segregation. 
Although the breeding of domestic ani- 
mals and plants has generally been di- 
rected toward the accentuation of some one 
feature or limited group of characteristics 
desirable for economic reasons, it should be 
remembered that, in nature, evolutionary 
progress must carry with it improvement 
in total organic efficiency, which in turn 
depends upon almost an infinity of mor- 
phological and physiological coordinations, 
the perfection of which would be assisted 
rather than hindered by the access to a great 
variety of evolutionary tendencies or sug- 
gestions. 
From the evolutionary standpoint a spe- 
cies is not a definition or a complex of char- 
acters, more or less important, but a group 
of organic individuals which stand in a 
definite biological relation of reproductive 
accessibility. Species do not arise and are 
not separated in nature primarily by the 
degree or amount of difference which may 
exist between individuals ; in some groups 
species contain greater diversities than ap- 
pear elsewhere between genera, families or 
orders. Interbreeding prevents the subdi- 
vision of species, but at the same time con- 
duces to variety instead of maintaining 
stability. Species become distinct in na- 
ture not only when the component individ- 
uals are separated by geographical or other 
forms of isolation, but accumulated varia- 
tions may themselves bring about isolation 
when evolutionary tendencies become so 
divergent that further coordination is diffi- 
cult, and interbreeding ceases. Evolution 
is thus a process of integration rather than 
SCIENCE. 
(N.S. Von. XIII. No. 338. 
of segregation, and organic progress, like 
intellectual and social advancement, is not 
an individual phenomenon, but the accu- 
mulated result of individual contributions 
which are not lost, but saved, by inter- 
breeding or communication to others. Iso- 
lation permits the accentuation of individ- 
ual peculiarities, but does not on that 
account conduce to intellectual or social 
development; selection may encourage spe- 
cialization, but it often limits the field of 
subsequent changes and adaptations neces- 
sary for the perpetuation and continued 
welfare of the species. 
The various forms of selection and isola- 
tion represent, as it were, the outside of 
evolution, the points at which it is affected 
by external accidents. Organic develop- 
ment is not, however, a passive, but an in- 
tensely active process; selection and isola- 
tion have not caused evolution, but are 
among the conditions under which it some- 
times proceeds. 
The crossing of geographically distinct 
species often results, not merely in the 
production of intermediate forms, but in 
new types having characters not repre- 
sented in either of the parents, and since 
the same result often follows the crossing 
of divergent forms of the same species, we 
have a further reason for believing that 
progressive change is not dependent upon, 
but may even be impeded by, selection and 
isolation, and that interbreeding rather than 
segregation is favorable to evolutionary 
progress. Static theories have thus re- 
versed the true functions and effects of 
panmixia and isolation. 
DARWINISM AS A STATIC THEORY. 
Phylogeny and ecology were combined by 
Darwin as different sides of the same phe- 
nomenon, and environment was held at 
once to cause variation and to produce in- 
definitely extensive changes by means of it 
—a theory here described as static because 
