Since this has being dug up from the old files, I'll post my two cents on this topic.
I think true leaders are born.
Nobody taught Alexander, Napoleon, Julius Caesar, Genghis Khan, Hitler, Xerxes, Odysseus, Leonidas, Attila, Hammurabi, Stalin, Lenin, Martin Luther King, Khufu, Ghandi, Winston Churchill, Lincoln, Thomas Jefferson or Frederick II how to do what they did.
Actually, most of those people you posted are kings/nobles or someone of high class. They were all taught to be a leader. The kings were taught when they were still a prince.
The other nobles went to good schools and things like that.
How about I tell you it's not one of the two ... imo ... I say your surroundings play one of the biggest parts in who you become ... let's say you could go back in time ... and we take one kid as an example ... And because we can go back in time, we can put the same kid in two different situations ...
In situation A the kid is raised by an abusing father and an alcoholic mother and stays there until he/she is 17 ... in this situation the kid realizes that he/she needs to do something about the life he/she had and gets a job and then later becomes the leader of an organization for kids with parents just like his/hers
In situation B the kid is raised by middle class parents that are loving and are happy with how the kid does at school and socially, the kid goes to college, studies something and gets a job ... no leader.
Now this could just as easily be the other way around, but what I'm saying is, is that your surroundings have a HUGE impact on who you become ... and I really think that that is the key factor.
I believe that this has a big factor into determining whether the kid would be a leader or not.
In your situation a, instead of him being repulsed to the abusive parents, (he could, I'm not throwing that possibility away), what I'm saying, that only strengthens the kids resolve and resilience. Makes the kid strong which is a big factor in leadership. After that s/he needs to nurture the leadership capabilities acquired during the surroundings. Hardship really changes people.
I'll bring in an example of my personal life in this. When I was young I used to be vary passive about what people do around me. I didn't really care since it didn't affect me. When I got to middle school and up, I started noticing myself giving people orders on where to stand during a baseball game or even dodge-ball
Later on though I stopped giving orders and became 'somewhat' passive. I'm not as passive as I used to be, but I'm also not as bossy as I used to be. By passive I mean I didn't really care for what others do around me, I didn't care to tell them what they are doing wrong/bad when I notice something that they have done that I feel is not right.
Now, I just let them notice, suggest a few things (if they are my friends) but I don't try and force them
Leadership can be born and can be trained. You just need to get the motivation, desire, and a real need for it. Like if you are in situation a in R_T's example, maybe it's not abusive parents, maybe it's just poverty, but you will get sick and tired of it and would like to turn things over. Maybe you would stay poor, but since you lived through it, you know how to survive, you are strengthened, then you are able to tell people what to do in poverty to survive.
Another thing I feel that goes into leadership is that you can be a leader in something you are very well versed. A poor guy wouldn't be a leader in telling people how to make money. A poor guy would be able to be a leader in telling people how to survive in those conditions.
An abused child could be a leader in surviving the parents. But that isn't where it ends. The skill in leadership can spread, like cancer spreads (bad example, I'm sorry).
Also, you can't be a leader if you haven't followed a leader.
Alright, this might have being more than 2 cents... sorry.