Natural nor sexual selection do not behave normally in modern humans. Nobody really dies due to being unfit (whether low IQ or otherwise) because our entire society is geared towards taking resources from the most fit to sustain the least fit. Everyone has about the same number of children and mate selection is complete chaos. As of last 1-2 centuries, I would not expect there to be any selective pressure favoring high IQ. In fact, our entire society is built to punish the fit to sustain the unfit. So I would expect that from now on IQ should decrease until it hits the absolute minimum necessary to survive. The resources will be redirected to maximizing procreation. So people will get dumber, less athletic, enter puberty earlier and become more promiscuous. This will go on until humans can just barely survive even with the systems and technology inherited from our day. Then as those systems eventually degrade or become insufficient due to changing environments, the degenerated humans will be unable to improve them, and the result will be a population collapse. Such a collapse could in theory provide the selective pressure to create a fitter population again, although it could also result in extinction. It is tempting to consider that an elite class could develop that does not interbreed with commoners and has a culture of strict meritocracy among themselves. However I doubt this will happen, because elites today believe most of their own bullshit and can't stop their kids from becoming degenerate. On the bright side, this stuff will take at least several generations, so likely we won't see the true Idiocracy in our lifetimes.