Louis Agassiz [pp. 103-105]

Louis Agassiz.
completion of what was then clearly conceived.
What, then, were the great ideas which underlay his life-work? These may doubtless
be gathered by the thoughtful reader from
the book before us; but they are not formally stated as we would state them. The
full significance of his work in scientific philosophy was, perhaps, imperfectly conceived
even by himself. I take this opportunity,
therefore, of expressing my own views on
this subject, because I believe that full justice has never been done Agassiz in this
regard.
Underlying Agassiz's whole life-work there
were two great ideas. One of these is the
idea of glaciers as a prime geological agent,
sculpturing mountains now, sculpturing a
large portion of the surface of the earth in
a former epoch. Glaciers had been ardently
studied before Agassiz, but only as a problem in physical geography. Agassiz transferred the subject into the wide field of
geology. He astonished the world by announcing a glacial epoch, immediately preceding the present, during which the northern portions of both continents, America
down to latitude 40~ and Europe to latitude
50~, were sheeted with ice several thousand
feet thick, and the whole surface of the land
modified by this agent. After a period of
fierce conflict, his views are now universally
accepted, and the whole field of geological
thought has been revolutionized thereby.
The second grand idea introduced by
Agassiz is still more important and far reaching in its effects. It was the idea that in each
family of animals the succession of forms in
geological history is epitomized in embryonic
changes of existing forms, and thus that embryology furnishes the key to geological succession. This idea is the very basis of the theory of evolution. Embryonic development
is not only evolution: it is the type of all evolution. What I mean by evolution is a
process similar to embryonic development.
Now, Agassiz showed that the process of
development of the organic kingdom in geological times is similar to the process of development of the embryo, and therefore is a
process of evolution so far as form is concerned. It is true that, for reasons which
I will presently give, he used the word development instead of evolution. Furthermore, he announced all the laws of geological succession as we now know them, and
showed that they are also the laws of embryonic development. Thus the whole
foundation of a scientific theory of evolution
was laid by him, and by him alone. The
theory of evolution owes as much to him as
to any other man, not excepting Darwin
himself. To him more than to any one man
is due the great impulse to biological science
and to modern thought associated with that
theory; for the most fruitful ideas and methods of biological science were introduced
by him. But because he rejected the theory
of evolution, as propounded by Darwin, his
true relation to modern thought is still unrecognized.
What, then, is the essential difference between the development theory of Agassiz and
the evolution theory of Darwin? I answer:
It was not in the process, but in the force of
change. Agassiz refused to believe that the
force of development of the organic kingdom
throughout geological time was inherent in
the thing developing in the same sense as it
is in the embryo. He compared the process
to the development of a building under the
hand of an intelligent architect. For him,
new species cannot be formed by transmutations from previously existing species, but
only by direct creative act; although the
successively created forms follow each other
in a regular order, and according to laws
which he has shown to be the laws of embryonic development. By refusing to acknowledge the origin of species by natural process,
he placed the whole subject of origin of species outside of the domain of science, for
science deals with the natural, not the supernatural. In a word, he laid solidly the
whole foundation of a true scientific theory
of evolution, and then refused to build thereon.
There is, to me, something supremely grand
even in this refusal. The opportunity to become the leader of modern thought, the fore
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[Janl.