Perhaps jealousy is an evolutionary process that makes us want to be better, try harder, or break away from one another so we don't hold each other back.
Hmm maybe at its core, though from what I've seen, most people don't treat it as such. Seems that the number of people who say someone being better, and felt inspired to take control over their own life can be counted on one hand.
I think it's a survival, cave brain thing, jealousy. You had to keep a close eye on how much your neighbor's got, and how he's doing, because it meant better chances at survival for his genes. Those who were worse off weren't a threat. Though I think in caveman times, people would've been way more incentivized to try a little harder, since they understood what was at stake... so maybe you're right on that.
In modern times, though, it seems we're a world-full of losers, and most people don't seem all that bothered by the concept.
I think these days it is interesting to see that people have to apologise for losing weight, to those who won't lose weight themselves.
I agree with the caveman analogy, but at the same time back then, it was impossible to survive alone. This meant that there was more of a share system, each doing their task and appreciated for it - I wonder if it was once we started to settle down and compartmentalize as a society, that this started to change.