In "The Giver" where did the idea of "Sameness" come from, and why were there no differences in people other than gender and assigned jobs?

The people of the community were trying to eliminate sources of unhappiness. They believed that if no one had any more or less than another, had the same amount of love for every person, then everyone would be equal and therefore equally happy. They didn't see the need for the advances that come from competition between people of varying abilities and with different interests; as far as they were concerned, things were perfect the way they were, and there was no need for any change.