I stress and multiply examples because the power of environment is so tremendous that we can hardly over-rate its importance.
A child is not born with a conscience; but with the rudiments of a conscience: the materials from which a conscience may or may not be developed—by environment.
A child is not born with capacities, but only with potentialities, or possibilities, for good or evil, which may or may not be developed—by environment.
A child is born absolutely without knowledge. Every atom of knowledge he gets must be got from his environment.
Every faculty of body or of mind grows stronger with use and weaker with disuse. This is as true of the reason and the will as of the muscles.
The sailor has better sight than the townsman, because his eyes get better exercise. The blind have sharper ears than ours, because they depend more on their hearing.
Exercise of the mind "alters the arrangement of the grey matter of the brain," and so alters the morals, the memory, and the reasoning powers.
Just as dumb-bells, rowing, or delving develop the muscles, thought, study, and conversation develop the brain.
And everything that changes, or develops, muscle or brain is a part of our environment.
There must be bounds to the powers of environment, but no man has yet discovered the limits, and few have dared to place them wide enough.