Paul Krugman says he's been getting hatemail calling him the new Thomas Malthus. (Which actually strikes me as pretty thoughtful, high-minded hatemail.) Paul responds by pointing out that Thomas Malthus was actually right for just about all of human history, and reprints a graph from Brad DeLong to prove it.
I have slightly different graph on this point, drawn from Gregory Clark's fantastic A Farewell To Alms. (IMHO the book really is worth a read.) The graph is, quite simply, the economic history of the entire world:
For pretty much all of human history, population growth constrained growth in real standards of living. (That's the "Malthusian Trap" above: as standards of living improved, population increased, which put a strain on resources and drove down standards of living, which in turn drove down population growth, rinse & repeat.) The industrial revolution broke this trap, although it's worth pointing out the fairly obvious fact that this is not true for the entire world -- which is why the graph is labeled the "Great Divergence" and not the "Unmitigated Triumph."
An interesting question about the history of economics is whether (and why) we should continue to assume the kind of rapid growth that has characterized western economies since 1800. It hasn't been around forever.