Origin of Species Variorum

→ to 1859 1860 1861 1866

by beasts of prey to 1869

↑ 3 blocks not present in 1859 1860 1861 1866 1869; present in 1872

It appears probable that disuse has been the main agent in rendering organs rudimentary. It would at first lead by slow steps to the more and more complete reduction of a part, until at last it became rudimentary,— as in the case of the eyes of animals inhabiting dark caverns, and of the wings of birds inhabiting oceanic islands, which have seldom been forced by beasts of prey to take flight, and have ultimately lost the power of flying. Again, an organ, useful under certain conditions, might become injurious under others, as with the wings of beetles living on small and exposed islands; and in this case natural selection will have aided in reducing the organ, until it was rendered harmless and rudimentary.

→ function, 1859 1860 1861 1866

structure and function, 1869 1872

→ An organ, 1859 1860 1861 1866 1869

Organs, originally formed by the aid of natural selection, 1872

→ when 1859 1860 1861 1866 1872

originally formed by the aid of natural selection, when 1869

↑ 1 blocks not present in 1859 1860 1861 1866 1869; present in 1872

All this agrees well with what we see under nature.

→ to 1859 1860 1861 1866

has to exert 1869 1872

→ reproduce 1859 1860 1861 1866 1869

tend to reproduce 1872

→ age, and consequently 1859 1860 1861

age, but 1866

mature age, but 1869 1872

→ relative size of rudimentary organs in the embryo, 1859 1860 1861 1866

size of rudimentary organs in the embryo relatively to its other parts, 1869

size of rudimentary organs in the embryo relatively to the adjoining parts, 1872

→ (as we have good reason to believe 1859 1860 1861 1866

the rudimentary part would tend 1869

I believe that disuse has been the main agency; that it has led in successive generations to the gradual reduction of various organs, until they have become rudimentary,— as in the case of the eyes of animals inhabiting dark caverns, and of the wings of birds inhabiting oceanic islands, which have seldom been forced →to take flight, and have ultimately lost the power of flying. Again, an organ useful under certain conditions, might become injurious under others, as with the wings of beetles living on small and exposed islands; and in this case natural selection would continue slowly to reduce the organ, until it was rendered harmless and rudimentary. ↑

Any change in →function, which can be effected by

~~insensibly~~

insensibly

small

stages,

steps,

is within the power of natural selection; so that an organ rendered,

through

during

changed habits of life, useless or injurious for one purpose, might

easily

....

be modified and used for another purpose.

Or an

organ

might,

might

also, be

retained for one alone of its former functions. →An organ, →when rendered

useless

useless,

may well be variable, for

their

its

variations

can no

cannot

longer be

checked by natural selection. ↑

Moreover, at

whatever period of life

either disuse

disuse

or selection reduces an organ, and this will generally be when the being has come to maturity and →to its full powers of action, the principle of inheritance at corresponding ages will →reproduce the organ in its reduced state at the same →age, and consequently will seldom affect

~~or reduce~~

or reduce

it in the embryo. Thus we can understand the greater →relative size of rudimentary organs in the embryo, and their lesser relative size in the adult. But if each step of the process of reduction were to be inherited, not at

the

corresponding age, but at

a very

an extremely

early period of

life,

life

→(as we have good reason to believe