at the moral point of view that
they place themselves when they connect their economic history with
Darwin's work. Thanks to this unifying hypothesis, they claim to have
constructed--as Marx does in his preface to _Das Kapital_--a veritable
natural history of social evolution. Engels speaks in praise of his
friend Marx as having discovered the true mainspring of history hidden
under the veil of idealism and sentimentalism, and as having
proclaimed in the _primum vivere_ the inevitableness of the struggle
for existence. Marx himself, in _Das Kapital_, indicated another
analogy when he dwelt upon the importance of a general technology for
the explanation of this psychology:--a history of tools which would be
to social organs what Darwinism is to the organs of animal species.
And the very importance they attach to tools, to apparatus, to
machines, abundantly proves that neither Marx nor Engels were likely
to forget the special characters which mark off the human world from
the animal. The former always remains to a great extent an artificial
world. Inventions change the face of its institutions. New modes of
production revolutionise not only modes of government, but modes even
of collective thought. Therefore it is that the evolution of society
is controlled by laws special to it, of which the spectacle of nature
offers no suggestion.

If, however, even in this special sphere, it can still be urged that
the evolution of the material conditions of society is in accord with
Darwin's theory, it is because the influence of the methods of
production is itself to be explained by the incessant strife of the
various classes with each other. So that in the end Marx, like Darwin,
finds the source of all progress is in struggle. Both are grandsons of
Heraclitus:--[Greek: polemos pater panton]. It sometimes happens, in
these days, that the doctrine of revolutionary socialism is contrasted
as rude and healthy with what may seem to be the enervating tendency
of "solidarist" philanthropy: the apologists of the doctrine then
pride themselves above all upon their faithfulness to Darwinian
principles.

* * * * *

So far we have been mainly concerned to show the use that social
philosophies have made of the Darwinian laws for practical purposes:
in order to orientate society towards their ideals each school tries
to show that the authority of natural science is on its side. But even
in the most objective o