Origin of Species Variorum

→ to lay very little 1859 1860 1861 1866

not to lay much 1869

to lay less 1872

→ action 1859 1860 1861 1866 1872

and definite action 1869

→ conditions of life. 1859 1860 1861 1866

conditions of life; but I fully admit that strong arguments of a general nature may be advanced on the other side. 1869

surrounding conditions, than on a tendency to vary, due to causes of which we are quite ignorant. 1872

↑ 2 blocks not present in 1859 1860 1861; present in 1866 1869 1872

In a far-fetched sense, however, the conditions of life may be said, not only to cause variability, but likewise to include natural selection; for it depends on the nature of the conditions whether this or that variety shall be preserved. But we see in selection by man, that these two elements of change are essenitally distinct; the conditions under domestication causing the variability, and the will of man, acting either consciously or unconsciously, accumulating the variations in cretain definite directions.

→ Use and Disuse .— 1859 1860 1861

Use and Disuse, as controlled by Natural Selection. 1866

Use and Disuse, as controlled by Natural Selection . 1869

the increased Use and Disuse of Parts, as controlled by Natural Selection . 1872

→ duck. 1859 1860 1861 1866 1869

duck: it is a remarkable fact that the young birds, according to Mr. Cunningham, can fly, while the adults have lost this power. 1872

→ I believe 1859 1860 1861 1866 1869

it is probable 1872

conditions. Such facts show how indirectly the conditions of life

must

....

act. Again, innumerable instances are known to every

naturalist,

naturalist

of species keeping true, or not varying at all, although living under the most opposite climates. Such considerations as these incline me →to lay very little weight on the direct →action of the →conditions of life. Indirectly, as already remarked, they seem to play an important part in affecting the reproductive system, and in thus inducing variability; and natural selection will then accumulate all profitable variations, however slight, until they become plainly developed and appreciable by us. ↑

Effects

→ Use and Disuse .—

From the facts alluded to in the first chapter, I think there can be

little

doubt that use in our domestic animals

has strengthened

strengthens

and

enlarged

enlarges

certain parts, and disuse

diminished

diminishes

them; and that such modifications are inherited. Under free nature, we

~~can~~

can

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

have

structures which can be

ex- plained

best explained

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. As the larger ground-feeding birds seldom take flight except to escape danger, →I believe that the nearly wingless condition of several birds,

~~which~~

which

now

inhabiting

inhabit

which

have

lately inhabited several oceanic islands, tenanted by no beast of prey, has been caused by disuse. The ostrich indeed inhabits

continents,

continents

and is exposed to danger from which it cannot escape by flight, but

~~by kicking~~

by kicking

it can defend