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OriginOfSpecies - 475 Rows
Column Type #Values Column Stats
id int(11) 475 Column Stats
subject varchar(80) 14 Column Stats
title varchar(250) 139 Column Stats
ordinal int(11) 30 Column Stats
description text 474 Column Stats

475 rows, page 103 of 119 (4/p)
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06 - Difficutiles in Theory 06-05 - Diversified Habits in the Same Species 10 I will now give two or three instances both of diversified and of changed habits in the individuals of the same species.

In either case it would be easy for natural selection to adapt the structure of the animal to its changed habits, or exclusively to one of its several habits.

It is, however, difficult to decide, 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 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.

England
England

insect
insect


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 a kingfisher at a fish.

Tyrant Flycatcher
Tyrant Flycatcher

South America
South America

kestrel
kestrel

kingfisher
kingfisher


In our own country the larger titmouse (Parus major) may be seen climbing branches, almost like a creeper; it sometimes, 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.
England
England

titmouse
titmouse

seeds
seeds

yew
yew


In North America the black bear was seen by Hearne swimming for hours with widely open mouth, thus catching, almost like a whale, insects in the water.

bear
bear
whale
whale
06 - Difficutiles in Theory 06-06 - Species with Habits Widely Diffferent from those of their Allies 10 Petrels are the most aerial and oceanic of birds, but in the quiet sounds of Tierra del Fuego, the Puffinuria berardi, in its general habits, in its astonishing power of diving, in its manner of swimming and of flying when made to take flight, would be mistaken by any one for an auk or a grebe; nevertheless it is essentially a petrel, but with many parts of its organisation profoundly modified in relation to its new habits of life; whereas the woodpecker of La Plata has had its structure only slightly modified.

In the case of the waterouzel, the acutest observer by examining its dead body would never have suspected its subaquatic habits; yet this bird, which is allied to the thrush family, subsists by diving- using its wings under water, and grasping stones with its feet.
petrel
petrel

Tierra del Fuego
Tierra del Fuego

auk
auk


All the members of the great order of hymenopterous insects are terrestrial excepting the genus Proctotrupes, which Sir John Lubbock has discovered to be aquatic in its habits; it often enters the water and dives about by the use not of its legs but of its wings, and remains as long as four hours beneath the surface; yet it exhibits no modification in structure in accordance with its abnormal habits.
06 - Difficutiles in Theory 06-03 - Absence or Rarity of Transitional Varieties 10 But, as by this theory innumerable transitional forms must have existed, why do we not find them embedded in countless numbers in the crust of the earth?

It will be more convenient to discuss this question in the chapter on the Imperfection of the Geological Record; and I will here only state that I believe the answer mainly lies in the record being incomparably less perfect than is generally supposed.


The crust of the earth is a vast museum; but the natural connections have been imperfectly made, and only at long intervals of time.

fossil
fossil
05 - Laws of Variation 05-13 - Summary 10 Our ignorance of the laws of variation is profound.

Not in one case out of a hundred can we pretend to assign any reason why this or that part has varied.

But whenever we have the means of instituting a comparison, the same laws appear to have acted in producing the lesser differences between varieties of the same species, and the greater differences between species of the same genus.

Changed conditions generally induce mere fluctuating variability, but sometimes they cause direct and definite effects; and these may become strongly marked in the course of time, though we have not sufficient evidence on this head.

Habit in producing constitutional peculiarities and use in strengthening and disuse in weakening and diminishing organs, appear in many cases to have been potent in their effects.

Homologous parts tend to vary in the same manner, and homologous parts tend to cohere.

Modifications in hard parts and in external parts sometimes affect softer and internal parts.

When one part is largely developed, perhaps it tends to draw nourishment from the adjoining parts; and every part of the structure which can be saved without detriment will be saved.

Changes of structure at an early age may affect parts subsequently developed; and many cases of correlated variation, the nature of which we are unable to understand, undoubtedly occur.

Multiple parts are variable in number and in structure, perhaps arising from such parts not having been closely specialised for any particular function, so that their modifications have not been closely cheeked by natural selection.

It follows probably from this same cause, that organic beings low in the scale are more variable than those standing higher in the scale, and which have their whole organisation more specialised.

Rudimentary organs, from being useless, are not regulated by natural selection, and hence are variable.

Specific characters- that is, the characters which have, come to differ since the several species of the same genus branched off from a common parent- are more variable than generic characters, or those which have long been inherited, and have not differed from this same period.