Human stupidity; it is the foundation of all major societies and cultures. While humans have the greatest capability for intelligence of all animals, our thinking is also the most irrational and error-prone, ie. stupid. Only a few geniuses rise significantly above the norm, and are the ones doing the thinking that once in a while leads to a significant burst of progress, though it is almost always fought against by the braindead mob at first. Humans, with a few exceptions, such as (to varying degrees) some of the people like us, and a few others whose intelligence enables them to sort out their stupidity (in computer terms, debug themselves), are herd animals. Mindless, useless, fucking morons who live only to gain the useless respect of their equally stupid peers, oppress anyone who doesn't fit tightly enough into the patterns that their society (as well as, on a smaller scale, social groups) follow for the moment, and do their best to force those better than themselves to operate at their level of stupidity.
Humanity has worked this way for all of its history, and will continue doing so until it is either wiped out, forcibly changed (perhaps a bunch of the best will one day manage to take control of the world and get it into shape; as technology progresses, the means for doing so will gradually appear. it is not likely to happen, though), or (should it survive long enough, something thankfully not all that likely) evolves into something else, whether it be less or more stupid.
What would be needed would be for a bunch of mad scientists, the kind that would completely disregards all existing norms and obsessively work towards their goals, to take over the world. Through genetic engineering, human nature could be improved. A strong enough world government could attain what would be needed to take absolute control over human reproduction; from there, every new generation could be given a set of genetic improvements, and over a few hundred years, humanity could evolve atleast partially out of its current, miserable state.
During the process though, a temporary solution would have to be used to reduce the influence of human stupidity, by enforcing rationality. Those who are incapable of making rational decisions would be forced to undergo therapy to correct their faults, if possible, or made incapable (depending on their usefulness, they could either be made into mindless slaves or executed. the latter is also a fine solution for the overpopulation problem) of decision-making.
Alternatively, as the chance of humanity being able to rid itself of its stupidity any other way is very slim, the most efficient solution would be the eradication of humanity.