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lost its scales because it buries itself in the sand and does not need them. 
or whether it buries itself in the sand because it has no scales and needs 
protection, or whether burying itself in the sand there has come to be a 
gradual selection of those whose scales are fewest and thinnest. Anyhow, 
we were sure of its origin, and that it was descended from some of the 
other forms of dwarf perch te that called the Johnny Darter. 
Many men before Darwin had taught the theory of descent, but Dar- 
win gave the first rational exposition of how it came about by natural 
processes. He showed that adaptation is the natural result of the sur- 
vival of the adapted in the struggle for existence. Variation is every- 
Where among animals and plants. No two animals or plants are ever 
avlike. There is everywhere a great wealth of life—more are born than 
can mature, and those survive and live who are able to fit themselves into 
the scheme of life. Darwin did not believe in evolution in vacuo, that is, 
evolution wholly independent of external circumstances and conditions, 
but this heresy that the laws of evolution, which are simply the way 
things come about, can produce evolution and divergence without any ex- 
cept metaphysical causes, still has a large body of followers. It is, in my 
judgment, one of the heresies of the present time. 
In the evolution of any species in the rough-and-tumble of life, we 
have these four elements: Variation, heredity, selection and segregation. 
Variation is the starter. It is interwoven with the operation of heredity. 
The favorable variation survives, and the animal or plant possessing it 
gives rise to the next generation. This is selection. 
The operation of isolation is this: A group becomes separated by some 
barrier which the individual can not cross. Little by little the species be- 
come separated into two or more species, one just as well adapted as the 
other. It is not often that differences between species are differences in 
adaptation. It is therefore not often that they are due to natural selec- 
tion. The final difference, the final polishing or rounding off of the species 
giving it its distinctive minor character, is due to isolation. Variation 
and heredity are inside the individual. The incidents of selection and 
isolation are of the outside world. They are part of the modifying con- 
ditions of life. Without contact with the outside influences, in my be- 
lief, there is no evolution. 
Darwin may be compared to an explorer in a new country. From 
some high point he makes a map of the country, locating its salient fea- 
