"An animal which differs from another by some decided and permanent
character, however slight, which difference is undiminished by
propagation and unchanged by climate and external circumstances, is
universally held to be a distinct _species_; while one which is not
regularly transmitted so as to form a distinct race, but is occasionally
reproduced from the parent stock (like albinoes), is generally, if the
difference is not very considerable, classed as a _variety_. But I would
class both these as distinct _species_, and I would only consider those
to be _varieties_ whose differences are produced by external causes, and
which, therefore, are not propagated as distinct races."
Again, writing about the same period, he adds: "I begin to feel rather
dissatisfied with a mere local collection; little is to be learnt by it.
I should like to take some one family to study thoroughly, principally
with a view to the theory of the origin of species. By that means I am
strongly of opinion that some definite results might be arrived at." And
he further alludes to "my favourite subject--the variations,
arrangements, distribution, etc.
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