re: When did the idea that we're all "created equally" become a widely held belief?

“Up to a point a person’s life is shaped by environment, heredity, and changes in the world about them. Then there comes a time when it lies within their grasp to shape the clay of their life into the sort of thing they wish it to be. Only the weak blame parents, their race, their times, lack of good fortune or the quirks of fate. Everyone has the power to say, "This I am today. That I shall be tomorrow.”
? Louis L'Amour, The Walking Drum


Am currently reading this book and just came across this little gem last night