Comparison with 1859 |
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had come to a high stage of perfection, so as to have given them a decided advantage over other animals in the battle for life. Hence the chance of discovering species with transitional grades of structure in a fossil condition will always be less, from their having existed in lesser numbers, than in the case of species with fully developed structures. |
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I will now give two or three instances
of of 1859 1860 1861 1866 1869 | both of 1872 |
diversified and of changed habits in the individuals of the same species.
When When 1859 1860 1861 1866 | In 1869 1872 |
either case
occurs, occurs, 1859 1860 1861 1866 | occurs, 1869 1872 |
it would be easy for natural selection to
fit fit 1859 1860 1861 1866 | adapt 1869 1872 |
the
animal, by some modification of its structure, for animal, by some modification of its structure, for 1859 1860 1861 1866 |
structure of the animal to 1869 1872 |
its changed habits, or exclusively
for for 1859 1860 1861 1866 | to 1869 1872 |
one of its several
different different 1859 1860 1861 1866 | different 1869 1872 |
habits.
But it is But it is 1859 1860 1861 1866 |
It is, however, 1869 1872 |
difficult to
tell, tell, 1859 1860 1861 1866 | decide, 1869 1872 |
and immaterial for us, whether habits generally change first and structure afterwards; or whether slight modifications of structure lead to changed habits; both probably often
change change 1859 1860 1861 1866 | occurring 1869 1872 |
almost simultaneously. Of cases of changed habits it will suffice merely to allude to that of the many British insects which now feed on exotic plants, or exclusively on artificial substances. Of diversified habits innumerable instances could be given: I have often watched a tyrant flycatcher (Saurophagus sulphuratus) in South America, hovering over one spot and then proceeding to another, like a kestrel, and at other times standing stationary on the margin of water, and then dashing
like like 1859 1860 1861 |
into it like 1866 1869 1872 |
a kingfisher at a fish. In our own country the larger titmouse (Parus major) may be seen climbing branches, almost like a creeper; it
often, often, 1859 1860 1861 1866 | sometimes, 1869 1872 |
like a shrike, kills small birds by blows on the head; and I have many times seen and heard it hammering the seeds of the yew on a branch, and thus breaking them like a nuthatch. In North America the black bear was seen by Hearne swimming for hours with widely open mouth, thus catching,
like like 1859 | almost like 1860 1861 1866 1869 1872 |
a whale, insects in the water. Even in so extreme a case as this, if the supply of insects were constant, and if better adapted competitors did not already exist in the country, I can see no difficulty in a race of bears being rendered, by natural selection, more and more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale. |
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As we sometimes see individuals
of a species of a species 1859 1860 1861 1866 1869 |
OMIT 1872 |
following habits
widely widely 1859 1860 1861 1866 1869 | widely 1872 |
different from those
both of their own both of their own 1859 |
of their own 1860 1861 1866 1869 |
proper to their 1872 |
species and
of of 1859 1860 1861 1866 1869 | to 1872 |
the other species of the same genus, we might
expect, expect, 1859 1860 1861 1866 | expect 1869 1872 |
on my theory, on my theory, 1859 1860 1861 1866 |
OMIT 1869 1872 |
that such individuals would occasionally
have have 1859 1860 1861 1866 | have 1869 1872 |
given given 1859 1860 1861 1866 | give 1869 1872 |
rise to new species, having anomalous habits, and with their structure either slightly or considerably modified from that of their
proper proper 1859 1860 1861 1866 1869 | proper 1872 |
type. And such instances
do do 1859 1860 1861 1866 1869 | do 1872 |
occur in nature. Can a more striking instance of adaptation be given than that of a woodpecker for climbing trees and
for for 1859 1860 1861 1866 | for 1869 1872 |
seizing insects in the chinks of the bark? Yet in North America there are woodpeckers which feed largely on fruit, and others with elongated wings which chase insects on the
wing; wing; 1859 1860 | wing. 1861 1866 1869 1872 |
and on and on 1859 1860 | On 1861 1866 1869 1872 |
the plains of La Plata, where
not not 1859 1860 1861 1866 1869 | hardly 1872 |
a tree grows, there is a
woodpecker, woodpecker, 1859 1860 | woodpecker 1861 1866 1869 1872 |
which in every essential part of its organisation, even in its colouring, which in every essential part of its organisation, even in its colouring, 1859 1860 |
(
Colaptes campestris
) which has two toes before and two behind, a long pointed tongue, stiff pointed tail feathers, but not so stiff as
1861 |
(
Colaptes campestris
) which has two toes before and two behind, a long pointed tongue, stiff pointed tail-feathers, but not so stiff as
1866 |
(
Colaptes campestris
) which has two toes before and two behind, a long pointed tongue, pointed tail-feathers, sufficiently stiff to support the bird in a vertical position on a post, but not so stiff as
1869 |
(Colaptes campestris) which has two toes before and two behind, a long pointed tongue, pointed tail-feathers, sufficiently stiff to support the bird in a vertical position on a post, but not so stiff as 1872 |
in the
harsh tone of its voice, and undulatory flight, told me plainly of its close blood-relationship to our common species; yet it is a woodpecker which never climbs a tree! harsh tone of its voice, and undulatory flight, told me plainly of its close blood-relationship to our common species; yet it is a woodpecker which never climbs a tree! 1859 1860 |
typical woodpeckers (yet I have seen it use its tail when alighting vertically on a post), and a straight strong beak. 1861 1866 |
typical woodpeckers, and a straight strong beak. 1869 1872 |
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