Evolution requires an outside stress that has a favorable mutation in the gene somewhere that gets passed along and changes something down the line. Unfortunately, we've peaked and now can control nature for the most part, so no longer have an outside force driving a change in how we are. if anything, the fruits of out labor have allowed the less fit genetic material to be passed on because there is no interference from nature.
So until such a time as we all get super powers from radon gas, or the aliens come back to do it with us again, and hopefully not re enslave us, we'll be stuck getting stupider.
