I think a gentleman is someone who holds the comfort of other people above their own. The instinct to do that is inside every good man, I believe. The rules about opening doors and buying dinner and all of that other 'gentleman' stuff is a chess game, especially these days.
It is one thing for the human mind to extract from the phenomena of nature the laws which it has itself put into them; it may be a far harder thing to extract laws over which it has no control.