ves to be called natural. The true relationship of organisms is
brought before one by considering relations of analogy, an otter-like
animal amongst mammalia and an otter amongst marsupials. In such cases
external resemblance and habit of life and _the final end of whole
organization_ very strong, yet no relation{136}. Naturalists cannot
avoid these terms of relation and affinity though they use them
metaphorically. If used in simple earnestness the natural system ought
to be a genealogical <one>; and our knowledge of the points which are
most easily affected in transmission are those which we least value in
considering the natural system, and practically when we find they do
vary we regard them of less value{137}. In classifying varieties the
same language is used and the same kind of division: here also (in
pine-apple){138} we talk of the natural classification, overlooking
similarity of the fruits, because whole plant differs. The origin of
sub-genera, genera, &c., &c., is not difficult on notion of genealogical
succession, and accords with what we know of similar gradations of
affinity in domesticated organisms. In the same region the organic
beings are <illegible> related to each other and the external conditions
in many physical respects are allied{139} and their differences of same
kind, and therefore when a new species has been selected and has
obtained a place in the economy of nature, we may suppose that
generally it will tend to extend its range during geographical changes,
and thus, becoming isolated and exposed to new conditions, will slightly
alter and its structure by selection become slightly remodified, thus we
should get species of a sub-genus and genus,--as varieties of
merino-sheep,--varieties of British and Indian cattle. Fresh species
might go on forming and others become extinct and all might become
extinct, and then we should have <an> extinct genus; a case formerly
mentioned, of which numerous cases occur in Palaeontology. But more often
the same advantages which caused the new species to spread and become
modified into several species would favour some of the species being
preserved: and if two of the species, considerably different, each gave
rise to group of new species, you would have two genera; the same thing
will go on. We may look at case in other way, looking to future.
According to mere chance every existing species may generate another,
but if any species, A, in changing gets an advanta