about the baby thing, i'm talking about love upon meeting the person. while the baby is in the womb for that long, the mom has never faced the baby, know hi/her personality, what kind of person they will be, etc. and despite that will still love them instantly from birth (at least they should...)
as for firemen and policemen, you may call it a sense of duty, but I am sure no one becomes a fireman or policeman because thats how you really rake in the money. there has to be a sense of love somewhere in there that transcends development issues that was talked about by darksoul.
the way i see it, love is like a pyramid of meanings, where the more superficial love stand at the bottom and the deeper love lies on top. of course everyone would have their own kinds of interpretations for what goes where.