is influence in an entirely original and peculiar way. He
acts as a ferment, and changes its constitution, just as the advent of
a new zoological species changes the faunal and floral equilibrium of
the region in which it appears. We all recollect Mr. Darwin's famous
statement of the influence of cats on the growth of clover in their
neighborhood. We all have read of the effects of the European rabbit
in New Zealand, and we have many of us taken part in the controversy
about the English sparrow here,--whether he kills most canker-worms, or
drives away most native birds. Just so the great man, whether he be an
importation from without like Clive in India or Agassiz here, or
whether he spring from the soil like Mahomet or Franklin, brings about
a rearrangement, on a large or a small scale, of the pre-existing
social relations.

{227}

The mutations of societies, then, from generation to generation, are in
the main due directly or indirectly to the acts or the example of
individuals whose genius was so adapted to the receptivities of the
moment, or whose accidental position of authority was so critical that
they became ferments, initiators of movement, setters of precedent or
fashion, centres of corruption, or destroyers of other persons, whose
gifts, had they had free play, would have led society in another
direction.

We see this power of individual initiative exemplified on a small scale
all about us, and on a large scale in the case of the leaders of
history. It is only following the common-sense method of a Lyell, a
Darwin, and a Whitney to interpret the unknown by the known, and reckon
up cumulatively the only causes of social change we can directly
observe. Societies of men are just like individuals, in that both at
any given moment offer ambiguous potentialities of development.
Whether a young man enters business or the ministry may depend on a
decision which has to be made before a certain day. He takes the place
offered in the counting-house, and is _committed_. Little by little,
the habits, the knowledges, of the other career, which once lay so
near, cease to be reckoned even among his possibilities. At first, he
may sometimes doubt whether the self he murdered in that decisive hour
might not have been the better of the two; but with the years such
questions themselves expire, and the old alternative _ego_, once so
vivid, fades into something less substantial than a dream. It is no
otherwise with n