It can come as no surprise that intelligence is inheritable, just as height, eye-color, and baldness are inheritable. Also, we know that in general, people with lesser intelligence have more children. The result is that we are literally effing ourselves stupid.
There is some correlation between IQ and survivability, which until recently kept our species intelligence on an upward track, but it is now national policy in the developed world to prevent stupidity from being fatal, to insulate people from the consequences of their stupidity.
This can be countered somewhat by better educational systems, but then more improvement would occur from those better educational systems if the average students were not becoming less capable of learning.
Perhaps we should stop subsidizing stupidity, and perhaps intelligent people should think about having more children.