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See page in:
1859
1860
1861
1866
1869
1872

Compare with:
1861
1866
1872

→ I will only remark that if 1869
If 1872
→ of two 1869
belonging to two distinct though 1872
→ species, I can believe that they might sometimes 1869
forms, it is conceivable that these might 1872
→ for convenience sake 1869
have all to 1872
→ two 1869
the descendants of two distinct 1872
↑ 4 blocks not present in 1859 1860 1861 1866 1869; present in 1872
But it would in most cases be extremely rash to attribute to convergence a close and general similarity of structure in the modified descendants of widely distinct forms. The shape of a crystal is determined solely by the molecular forces, and it is not surprising that dissimilar substances should sometimes assume the same form; but with organic beings we should bear in mind that the form of each depends on an infinitude of complex relations, namely on the variations which have arisen, these being due to causes far too intricate to be followed out,— on the nature of the variations which have been preserved or selected, and this depends on the surrounding physical conditions, and in a still higher degree on the surrounding organisms with which each being has come into competition,— and lastly, on inheritance (in itself a fluctuating element) from innumerable progenitors, all of which have had their forms determined through equally complex relations. It is incredible that the descendants of two organisms, which had originally differed in a marked manner, should ever afterwards converge so closely as to lead to a near approach to identity throughout their whole organisation. If this had occurred, we should meet with the same form, independently of genetic connection, recurring in widely separated geological formations; and the balance of evidence is opposed to any such an admission.
→ that from an early part of the long 1866 1869
at least within the whole immense 1861
that from an early part of the 1872
have overrated the importance of divergence of character (in which, however, he apparently believes), and that
convergence,
convergence
of character,
of character,
as it may be called, has likewise played a part. This is an intricate subject which need not be fully discussed. →I will only remark that if two
species,
species
→of two allied genera,
had both
both
produced a
large number
number
of new and divergent →species, I can believe that they might sometimes approach each other so closely that they would →for convenience sake be classed
under
in
the same
new
new
genus;
genus,
and thus →two genera would converge into
one.
one;
but
but
from
from
the
the
strength
strength
of
of
the
the
principle
principle
of
of
inheritance,
inheritance,
and
and
from
from
the
the
two
two
parent-species
parent-species
already
already
differing
differing
and
and
consequently
consequently
tending
tending
to
to
vary
vary
in
in
a
a
somewhat
somewhat
different
different
manner,
manner,
it
it
seems
seems
hardly
hardly
credible
credible
that
that
the
the
two
two
new
new
groups
groups
would
would
not
not
at
at
least
least
form
form
distinct
distinct
sections
sections
in
in
the
the
genus.
genus.
↑
Mr. Watson has also objected that the continued action of natural
selection,
selection
together with
with
divergence of
character,
character
would
will
tend to make an indefinite number of specific forms. As far as mere inorganic conditions are concerned, it seems probable that a sufficient number of species would soon become adapted to all considerable diversities of heat, moisture, &c.; but I fully admit that the mutual relations of organic beings are more important; and as the number of species in
any
any
anycountry
country
goes on increasing, the organic conditions of life
will
must
....
become more and more complex. Consequently there seems at first sight
to be
....
no limit to the amount of profitable diversification of structure, and therefore no limit to the number of species which might be produced. We do not know that even the most prolific area is fully stocked with specific forms: at the Cape of Good Hope and in Australia, which support such an astonishing number of species, many European plants have become naturalised. But geology shows us, →that from an early part of the long tertiary
period,
period