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
both of both of 1872 | of 1859 1860 1861 1866 1869 |
diversified and of changed habits in the individuals of the same species.
In In 1869 1872 | When 1859 1860 1861 1866 |
either case
....... 1869 1872 | occurs, 1859 1860 1861 1866 |
it would be easy for natural selection to
adapt adapt 1869 1872 | fit 1859 1860 1861 1866 |
the
structure of the animal to structure of the animal to 1869 1872 |
animal, by some modification of its structure, for 1859 1860 1861 1866 |
its changed habits, or exclusively
to to 1869 1872 | for 1859 1860 1861 1866 |
one of its several
....... 1869 1872 | different 1859 1860 1861 1866 |
habits.
It is, however, It is, however, 1869 1872 |
But it is 1859 1860 1861 1866 |
difficult to
decide, decide, 1869 1872 | tell, 1859 1860 1861 1866 |
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
occurring occurring 1869 1872 | change 1859 1860 1861 1866 |
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
into it like into it like 1866 1869 1872 |
like 1859 1860 1861 |
a kingfisher at a fish. In our own country the larger titmouse (Parus major) may be seen climbing branches, almost like a creeper; it
sometimes, sometimes, 1869 1872 | often, 1859 1860 1861 1866 |
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,
almost like almost like 1860 1861 1866 1869 1872 | like 1859 |
a whale, insects in the water. ↑1 blocks not present in 1860 1861 1866 1869 1872; present in 1859 | 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
...OMIT 1872 |
of a species 1859 1860 1861 1866 1869 |
following habits
....... 1872 | widely 1859 1860 1861 1866 1869 |
different from those
proper to their proper to their 1872 |
both of their own 1859 |
of their own 1860 1861 1866 1869 |
species and
to to 1872 | of 1859 1860 1861 1866 1869 |
the other species of the same genus, we might
expect expect 1869 1872 | expect, 1859 1860 1861 1866 |
...OMIT 1869 1872 |
on my theory, 1859 1860 1861 1866 |
that such individuals would occasionally
....... 1869 1872 | have 1859 1860 1861 1866 |
give give 1869 1872 | given 1859 1860 1861 1866 |
rise to new species, having anomalous habits, and with their structure either slightly or considerably modified from that of their
....... 1872 | proper 1859 1860 1861 1866 1869 |
type. And such instances
....... 1872 | do 1859 1860 1861 1866 1869 |
occur in nature. Can a more striking instance of adaptation be given than that of a woodpecker for climbing trees and
....... 1869 1872 | for 1859 1860 1861 1866 |
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. 1861 1866 1869 1872 | wing; 1859 1860 |
On On 1861 1866 1869 1872 | and on 1859 1860 |
the plains of La Plata, where
hardly hardly 1872 | not 1859 1860 1861 1866 1869 |
a tree grows, there is a
woodpecker woodpecker 1861 1866 1869 1872 | woodpecker, 1859 1860 |
(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 (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 |
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 |
in the
typical woodpeckers, and a straight strong beak. typical woodpeckers, and a straight strong beak. 1869 1872 |
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 |
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