[quote]How are individual differences a prerequisite for leadership? If so, what if someone is so different from others that they don't submit to proposed hierarchies, or refuse to be elevated within them?[/quote]

I wouldn't say they're a prerequisite, they just lead to it. If one person ends up being a leader while others did not, clearly that person had some trait or another which led to that outcome (and/or the other people were lacking in some certain personality trait). And sure you could have weird individuals who try to opt out or whatever. It doesn't even have to be leadership in a formal institution, just think about doing group work for a school project. This is work among peers and often times one person, or a couple of people, will end up taking a more assertive role in delegating tasks, just do to having more pro-active personalities.