I don't know about it being entirely "new", but i do think that it's at least partly cultural. In particular, I think Northern climates tend to encourage a tendency to over-produce when times are good, in order to prepare for when times are bad ("Winter is coming" ;). Hence the New England "Protestant work ethic", etc. Whereas more equatorial climates, with milder seasons and a general abundance of nutritious lifeforms, tend to encourage/allow a more day-by-day approach.
The social mobility issue is a whole separate question. Keep in mind that the rigid social strata of ancient civilizations were just as much a "new" construct in their day as our modern society is now. Obviously lower/middle classes who are actively prevented from improving their lot will eventually learn to stop trying. But that doesn't mean that that's a natural state of man; it may just be "learned helplessness" kicking in.
What would be more interesting would be to study people in more primal cultures. But the problem there is that there is a selection bias, in that the cultures that still live close to a state of nature are largely those that are biased against behaviors (including over-production) that would encourage their development into more structured civilizations.