物种起源（英文全本）is、as-全集TXT下载-免费全文下载

slightly

in a state

of nature.

No one

will

dispute

that

instincts

are of the

highest

importance

to each

animal.

Therefore

I can see

no

difficulty,

under

changing

conditions

of life,

in natural

selection

accumulating

slight

modifications

of

instinct

to any

extent, in

any useful

direction.

In some

cases

habit or

use and

disuse

have

probably

come into

play. I do

not

pretend

that the

facts

given in

this

chapter

strengthen

in any