Just a psychological curiosity, I guess, but one that called my attention.
The so-called reward-driven individuals demonstrated at tests that they are more motivated to win in general and that they win more often than their "normal" peers. However a paradox was found: when there was a monetary prize, the "normal" players actually improved their performance, making the "winner" type win less and perform more like the rest.
Full story at Science Daily.
This suggests to me that "reward-driven" could be a misnomer and that in fact we are before a personality type that is more "success-driven", with or without reward. This may have its rewards (in form of unexpected or hidden prizes and in the open rewards they also get, even if at lower rate) but it may also be costly in terms of energy spent (both mental and physical and even economic resources maybe). I do hence suspect that both phenotypes are in dynamic equilibrium.