Fun game! I really liked the different evolutions, they had a nice style going :) !
However, the currency did not really matter, the only limit on human output was how fast I could click the shopping cart. If I understood it right, the (upgrade?) arrow makes it so that if you click it like a hundred times, your "base" human will start at a later stage, saving you some time? So it was not obvious what the arrow button did.
Anyway, fun game with a nice ending!