All that said, fertility rates among the middle class are not zero. They may be below replacement rate (ok, they are below replacement rate), but being non-zero means evolution still applies.
Also, obviously in the wider population (that is, world-wide) we might well be selecting against traits that lead to middle-class status (by having lower fertility rates in the middle-class), but still, within middle-class populations we're likely still selecting for those traits.
Unless the middle class is a separate population to the rest of humanity then the evolution that is happening in the human population right now is selection against traits that lead to being middle class.
This selection is probably the strongest of any in human history looking at the demographic trends. When looked at dispassionately it is truely breath taking how huge this is.