970 
lies of Chilopoda represents the results of 
variation accumulated without the inter- 
ference of natural selection. In the next 
year* the same proposition was applied to 
the class Diplopoda, and studies in other 
groups, such as the termites, fungi, hepati- 
cz, mosses, ferns and flowering plants 
have led to the belief that there is little 
ground for the supposed stability of organic 
form and structure which furnished the 
basis of the doctrine of the separate creation 
of species, and which still figures as an im- 
portant postulate in theories of evolution 
through natural selection. The Diplopoda 
are one of the many classes of animals and 
plants in which ecologic relations are essen- 
tially different from those of the mammals, 
birds, and other highly specialized groups 
upon which evolutionary studies have 
largely been based. Among the Diplopoda 
are to be found very few of the adaptations 
sO numerous among the true insects ; Dip- 
lopoda do not eat each other, and are not 
eaten by other animals ;} their food require- 
ments are not specialized, and decaying veg- 
etable matter is generally abundant far in 
excess of their needs. There is seldom a 
suggestion of a struggle for existence or of 
other conditions indicating an active prin- 
ciple of selection. At the same time there 
is no lack of morphological differences, and 
while the present or past absence of select- 
ive influence in any particular character 
cannot, of course, be demonstrated, the phy- 
logenetic, biologic and ecologic unity of 
the group, when contrasted with its struc- 
tural and evolutionary diversity, seems to 
justify the opinion that in this class, at 
least, evolution is a kinetic phenomenon 
or active process of organic change, instead 
of the result of a passive subjection to ex- 
ternal interference in otherwise stable con- 
ditions. 
* American Naturalist, 1896, 30 : 682. 
{+ Sciencr, N. S., Vol. XII., October 5, 1900, p. 
518. 
SCIENCE. 
[N.S. Von. XIII. No 338. 
EVOLUTION BY INTEGRATION. 
Examples of groups of characters which 
it seems impossible to look upon as of select- 
ive origin have been noticed in another 
place.* Moreover, it is scarcely necessary to 
detail particular instances, since for a propo- 
sition partaking of the nature of a general 
law every biologist should find ample sup- 
porting evidence inside the field of his own 
specialty. Kinetic evolution is, indeed, 
nothing new, and requires for its formal 
recognition little beyond the most obvious 
facts of natural history; doubtless it would 
have been appreciated and accepted years 
ago had not makers of static theories pro- 
tected themselves against so simple an in- 
ference by inventing the so-called principle 
of panmixia, under which it is argued that 
spontaneous progressive change is impos- 
sible in a large group of individuals, because 
fortuitous variations occurring simultane- 
ously in all directions are brought back to 
a stable average by intercrossing. 
In reality, however, this proposition is 
worthy of little of the deference due toa 
mathematical axiom ; biologically it rests 
on unproved and apparently unprovable 
assumptions. We have by no means ascer- 
tained that the individuals of a species tend 
to vary equally in. all directions with re- 
spect to all their characters ; on the con- 
trary, some variations are much more com- 
mon than others. We have not ascertained 
that the crossing of individuals showing 
different variations always results in aver- 
age offspring ; we know instead that the 
next generation often exceeds both its par- 
ents in the accentuation of some new char- 
acteristic. In its logical development pan- 
mixia, if true, would constitute a demon- 
stration that individual variation acting 
through heredity cannot contribute to the 
evolutionary progress of a species ; it is as 
*¢The Diplopod Family Oxydesmidae,’ a paper 
prepared for the Proceedings of the U. S. National 
Museum. 
