DECEMBER 29, 1899. ] 
pression of the most characteristic and 
fruitful intellectual life of our age is the 
word evolution. The latter half of our cen- 
tury has been so dominated by that idea in 
all its thinking, that it may well be named 
the Age of Evolution. Wemay give as the 
date of the beginning of the new epoch the 
year 1858 ; and the Wittenberg theses of the 
intellectual reformation of our time were 
the twin papers of Darwin and Wallace, 
wherein was promulgated the theory of 
natural selection. 
And yet, of course, the idea of evolution 
was not new, when these papers were pre- 
sented to the Linnean Society. Con- 
sciously or unconsciously, the aim of science 
at all times must have been to bring events 
that seemed isolated into a continuous de- 
velopment. To exclude the idea of evolu- 
tion from any class of phenomena, is to 
exclude that class of phenomena from the 
realm of science. In the former half of our 
century, evolutionary conceptions of the 
history of inorganic nature had become 
pretty well established. ‘The nebular hy- 
pothesis was obviously a theory of planetary 
evolution. The Lyellian geology, which 
took the place of the catastrophism of the 
last century, was the conception of evolu- 
tion applied to the physical history of the 
earth. 
Nor had there been wanting anticipations 
of evolution within the realm of biology. 
The author of that sublime Hebrew psalm 
of creation, preserved to us as the first 
chapter of Genesis, was in his way a good 
deal of an evolutionist. ‘Let the earth 
bring forth,’ ‘let the waters bring forth,’ 
are words that point to a process of growth 
rather than to a process of manufacture in 
the origination of living beings. In crude 
and vague forms, the idea of evolution was 
held by some of the Greek philosophers. 
Just at the beginning of our century La- 
marck developed the idea of evolution into 
something like a scientific theory. Yet it 
SCIENCE, 
949 
is no less true that the epoch of evolution 
in human thought began with Darwin. 
Manifold suggestions there were of genetic 
relationships between different organisms, 
whether organic forms were studied by the 
systematist or the embryologist, the geog- 
rapher or the paleontologist ; but each and 
all found the path to any credible theory of 
organic evolution blocked by the stubborn 
fact that variations in species appeared 
everywhere to be limited in degree, and to 
oscillate about a central average type, in- 
stead of becoming cumulative from genera- 
tion to generation. In the Darwinian prin- 
ciple of natural selection, for the first time, 
was suggested a force, whose existence in 
nature could not be doubted, and whose 
tendency, conservative in stable environ- 
ment, progressive in changing environ- 
ment, would account at once for the per- 
manence of species through long ages, and 
for epochs of relatively rapid change. How- 
ever Darwin’s work may be discredited by 
the exaggerations of Weismannism, how- 
ever it may be minified by Neo-Lamarck- 
ians, it is the theory of natural selection 
which has so nearly removed the barrier in 
the path of evolution, impassable before, as 
to lead, first the scientific world, and later 
the world of thought in general, to a sub- 
stantially unanimous belief in the deriva- 
tive origin of species. Certain it is that no 
discovery since Newton’s discovery of uni- 
versal gravitation has produced so profound 
an effect upon the intellectual life.of man- 
kind. The tombs of Newton and Darwin 
lie close together in England’s Valhalla, 
and together their names must stand as the 
two great epoch-making names in the his- 
tory of science. 
Darwin’s discovery relates primarily to 
the origin of species by descent with modi- 
fication from preéxisting species. It throws 
no direct light upon the question of the 
origin of life. But analogy is a guide that 
we may reasonably follow in our think- 
