The lawsuit filed against the NFL by over 1, 400 retired players citing their injuries from concussions are a proximate threat to the league.

FORBES: The Death of the NFL

While evolution and food safety can't entirely account for the increased interest in smoke, the grilling industry credits the extended economic downturn as a proximate cause for its popularity.

WSJ: Move Over Bacon: Foodies Just Want the Smoke

Moreover, despite the obvious role of contraception as a proximate determinant of fertility, the additional effect of contraceptive availability or family planning on fertility is quantitatively small and explains very little cross country variation.

FORBES: UN Population Predictions: Up To 15 Billion by 2100