good and distinct species or mere varieties.
When a young naturalist commences the study of a group of organisms
quite unknown to him, he is at first much perplexed to determine what
differences to consider as specific, and what as varieties; for he
knows nothing of the amount and kind of variation to which the group is
subject; and this shows, at least, how very generally there is some
variation. But if he confine his attention to one class within one
country, he will soon make up his mind how to rank most of the doubtful
forms. His
general tendency will be to make many species, for he will become
impressed, just like the pigeon or poultry-fancier before alluded to,
with the amount of difference in the forms which he is continually
studying; and he has little general knowledge of analogical variation
in other groups and in other countries, by which to correct his first
impressions. As he extends the range of his observations, he will meet
with more cases of difficulty; for he will encounter a greater number
of closely-allied forms. But if his observations be widely extended, he
will in the end generally be enabled to make up his own mind which to
call varieties and which species; but he will succeed in this at the
expense of admitting much variation, and the truth of this admission
will often be disputed by other naturalists. When, moreover, he comes
to study allied forms brought from countries not now continuous, in
which case he can hardly hope to find the intermediate links between
his doubtful forms, he will have to trust almost entirely to analogy,
and his difficulties will rise to a climax.
Certainly no clear line of demarcation has as yet been drawn between
species and sub-species that is, the forms which in the opinion of some
naturalists come very near to, but do not quite arrive at the rank of
species; or, again, between sub-species and well-marked varieties, or
between lesser varieties and individual differences. These differences
blend into each other in an insensible series; and a series impresses
the mind with the idea of an actual passage.
Hence I look at individual differences, though of small interest to the
systematist, as of high importance for us, as being the first step
towards such slight varieties as are barely thought worth recording in
works on natural history. And I look at varieties which are in any
degree more distinct and permanent, as steps leading to more
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