Edit: for your edit that was what led to the thought. I wasn't sure if the roles were an artifact we kept in place or if it still had use today.
Roles have use in that they organize society. They tell all members in a society what to do and what's expected of them. The larger the society, the more you need some sort of ideological glue that can hold everyone together. Otherwise, everyone would have just splintered back off into the smaller packs that we see in other mammals. Religion was the most effective ideological glue for a long, long stretch of human history.
That said, it's important to recognize biological inclinations as well. After all, as social animals, we need to be inclined to form groups period in order for creating larger groups to be feasible. And we see these sorts of roles emerge even in the smaller groups of other mammals. Now, how much of our present idea of normative roles stems from biological urges and how much comes from millennia of cultural and social development is anyone's guess.
That was perfect. It gave me a lot of groundwork to use for research. Thanks for taking the time out to write all that up for me! ---
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