Some brief answers
I would hypothesize that rats developed their divided stomach first, which led to the loss of vomit function. The divided stomach is a way to store food and smooth metabolic cycles when access to food is sporadic and metabolic processes are difficult to regulate- as is the case with a warm blooded animal that spends most of its time hiding in a hole until large predators are away or asleep. This also would explain pica: clay and dirt is readily available in a hole.
Plumer wonders "why hegemony?"
The US is currently in a position very similar to the position of France after the war of spanish succession. We are the major power that was the last to entered the previous world war (WWII and Thirty Years), therefore we were left in the best position afterwords. In addition, the coalition that supported us as a superpower to counter balance another super power (US v. USSR, Bourbons v. Hapsburgs) is slowly dissolving due to the fact we won (fall of Berlin wall/ Eastern europe, War of spanish succession).
As for why republicans like to increase the defense budget: duh.
Plumber also wonders "what happens in a population decrease?"
You get rich bitch! When there are less people, there is more stuff (land, capital) per person. While there certainly are increasing returns to scale for human activity (labor, entrepreneurship) at certain levels, I believe our society (meaning everyone including the third world) has grown past that level (indeed, possibly all societies have a propensity to grow that far).
This is an example of a sudden widespread reduction in population that resulted in a situation where people had so much stuff lying around that they could afford to send large amounts of their stuff over the horizon, possibly never to return. Others found different ways to spend the new wealth.
A gradual reduction in population would probably have the same salutary effects, but without the chaos caused by a sudden drop in population.
Shakespear's sister asks "why are you so interested in politics?"