One of the most disconcerting things about infants is that they only smile when they are pleased. They stare at visitors with round grave eyes, and when the visitors try to amuse them, they display astonishment at the foolish antics of adults. But as soon as possible, their parents teach them to seem pleased by the company of people to whom they are utterly indifferent.

Bertrand Russell (1872-1970) English mathematician and philosopher

“On smiling,” New York American (1932-08-17)
    (Source)