Jack London "Call of the Wild"

This first theft marked Buck as fit to survive in the hostile
Northland environment. It marked his adaptability, his capacity
to adjust himself to changing conditions, the lack of which would
have meant swift and terrible death. It marked, further, the
decay or going to pieces of his moral nature, a vain thing and a
handicap in the ruthless struggle for existence. It was all well
enough in the Southland, under the law of love and fellowship, to
respect private property and personal feelings; but in the
Northland, under the law of club and fang, whoso took such things
into account was a fool, and in so far as he observed them he
would fail to prosper.

Not that Buck reasoned it out. He was fit, that was all, and
unconsciously he accommodated himself to the new mode of life.
All his days, no matter what the odds, he had never run from a
fight. But the club of the man in the red sweater had beaten into
him a more fundamental and primitive code. Civilized, he could
have died for a moral consideration, say the defence of Judge
Miller's riding-whip; but the completeness of his decivilization
was now evidenced by his ability to flee from the defence of a
moral consideration and so save his hide. He did not steal for
joy of it, but because of the clamor of his stomach. He did not
rob openly, but stole secretly and cunningly, out of respect for
club and fang. In short, the things he did were done because it
was easier to do them than not to do them.