M Database Inspector (cheetah)
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|OriginOfSpecies - 475 Rows|
|05 - Laws of Variation||05-02 - Use and Disuse of Parts, combined with Natural Selection, Organs of Flight and Vision||10||
From the facts alluded to in the first chapter, I think there can be no doubt that use in our domestic animals has strengthened and enlarged certain parts, and disuse diminished them; and that such modifications are inherited.
Under free nature, we have no standard of comparison, by which to judge of the effects of long-continued use or disuse, for we know not the parent-forms; but many animals possess structures which can be best explained by the effects of disuse.
As Professor Owen has remarked, there is no greater anomaly in nature than a bird that cannot fly; yet there are several in this state.
The logger-headed duck of South America can only flap along the surface of the water, and has its wings in nearly the same condition as the domestic Aylesbury duck: it is a remarkable fact that the young birds, according to Mr. Cunningham, can fly, while the adults have lost this power.
As the larger ground-feeding birds seldom take flight except to escape danger, it is probable that the nearly wingless condition of several birds, now inhabiting or which lately inhabited several oceanic islands, tenanted by no beast of prey, has been caused by disuse.
The ostrich indeed inhabits continents, and is exposed to danger from which it cannot escape by flight, but it can defend itself by kicking its enemies, as efficiently as many quadrupeds.
We may believe that the progenitor of the ostrich genus had habits like those of the bustard, and that, as the size and weight of its body were increased during successive generations, its legs were used more, and its wings less, until they became incapable of flight.
|01 - Variations Under Domestication||01-07 - Origin of Domestic Varieties from one or more Species||40||
From facts communicated to me by Mr. Blyth, on the habits, voice, constitution, and structure of the humped Indian cattle, it is almost certain that they are descended from a different aboriginal stock from our European cattle;
and some competent judges believe that these latter have had two or three wild progenitors,- whether or not these deserve to be called species.
This conclusion, as well as that of the specific distinction between the humped and common cattle, may, indeed, be looked upon as established by the admirable researches of Professor Rutimeyer.
With respect to horses, from reasons which I cannot here give, I am doubtfully inclined to believe, in opposition to several authors, that all the races belong to the same species.
|06 - Difficutiles in Theory||06-09 - Cases of Difficulty||30||
Fritz Muller, in order to test the conclusions arrived at in this volume, has followed out with much care a nearly similar line of argument.
Several families of crustaceans include a few species, possessing an air-breathing apparatus and fitted to live out of the water.
In two of these families, which were more especially examined by Muller and which are nearly related to each other, the species agree most closely in all important characters; namely, in their sense organs, circulating system, in the position of the tufts of hair within their complex stomachs, and lastly in the whole structure of the water-breathing branchiae, even to the microscopical hooks by which they are cleansed.
Hence it might have been expected that in the few species
belonging to both families which live on the land, the equally
important air-breathing apparatus would have been the same;
for why should this one apparatus, given for the same
purpose, have been made to differ, whilst all the other
important organs were closely similar or rather identical?
Fritz Muller argues that this close similarity in so many
points of structure must, in accordance with the views
advanced by me, be accounted for by inheritance from a
But as the vast majority of the species in the above two
families, as well as most other crustaceans, are aquatic in
their habits, it is improbable in the highest degree, that their
common progenitor should have been adapted for breathing
air was thus led carefully to examine the apparatus in the
air-breathing species; and he found it to differ in each in
several important points, as in the position of the orifices, in
the manner in which they are opened and closed, and in
some accessory details.
Now such differences are intelligible, and might even have
been expected, on the supposition that species belonging to
distinct families had slowly become adapted to live more and
more out of water, and to breathe the air.
For these species, from belonging to distinct families, would
have differed to a certain extent, and in accordance with the
principle that the nature of each variation depends on two
factors, viz., the nature of the organism and that of the
surrounding conditions, their variability assuredly would not
have been exactly the same.
Consequently natural selection would have had different
materials or variations to work on, in order to arrive at the
same functional result; and the structures thus acquired
would almost necessarily have differed.
On the hypothesis of separate acts of creation the whole
case remains unintelligible.
This line of argument seems to have had great weight in
leading Fritz Muller to accept the views maintained by me in
Another distinguished zoologist, the late Professor Claparide,
has argued in the same manner, and has arrived at the same
He shows that there are parasitic mites (Acaridae), belonging
to distinct sub-families and families, which are furnished with
These organs must have been independently developed, as
they could not have been inherited from a common progenitor;
and in the several groups they are formed by the modification
of the fore-legs,- of the hind-legs,- of the maxillae or lips,- and
of appendages on the under side of the hind part of the body.
|06 - Difficutiles in Theory||06-01 - Difficulties on the Theory of Descent with Modification||40||Fourthly, how can we account for species, when crossed, being sterile and producing sterile offspring, whereas, when varieties are crossed, their fertility is unimpaired?|