Why do humans do the things they do? Why is the human brain, so impressive in its computing capacity, overrun with dangerous and ill-advised behaviors? Communally, why do we build complex civilizations based on fantasies, lies and wishful thinking, compress ourselves into cramped and frustrating living spaces, then long for violent outlets (expressed either in reality or in movie and TV preference)? We fancy ourselves to be exceptionally intelligent, as animals go, but much of the time we appear to have no more agency than the blindly self-destructive victims of parasites.
Speaking of which, Carl Zimmer's Parasite Rex is the story of the perpetual struggle between large multicellular creatures (like us) and the parasites who feed off them. Parasites frequently specialize in mind control. The book describes numerous instances where parasites invade the brains of their hosts to make them, for instance, forget their fears of natural predators, the intent being to get the host eaten so the parasite can go on to its next life-stage in the new animal. For the benefit of parasitic reproduction, fish float in front of herons, ants wait atop grass stalks for hungry birds, caterpillars leave the safety of their camouflage. Another type of parasitic mind control involves hijacking the reproductive system of the host so that all nurturing instincts are directed at parasite offspring, while the host remains barren.
We have no evidence that the familiar human compulsions are caused by parasites, but it's likely they are caused by something other than the human intellect. What sort of intellect would long for war, for instance, as our species is known to do? Since suicidal behavior, which longing for war can exemplify (even provided with a "just cause"), longing for war per se might be judged by most human culture and medical practice as abnormal, belying an intellect that can be reasonably suspected to be a victim of mind control.
If our thralldom does not derive from parasites, the next best suspects are transposons, mysterious genetic manipulators that invade our DNA from outside. Genetic scientist don't know what transposons are, what they want- if anything- or where they come from. The latest thinking is that transposons account for the non-inherited differences between identical twins, and for significant non-inherited behaviors in everyone. Exactly what those behaviors are and what purposes they might serve is unknown.
Transposon theory provides less explanation than parasite study, because at least with parasites we know the host is forced to serve the survival interests of a hostile life form. We don't even know if transposons are alive, let alone promoting an agenda. We only know they are there, influencing us.
Zimmer paints a vivid picture of the perennial war between parasites and their hosts. The genetic blueprints of both parties change dramatically and quickly as they interact, keeping the balance of power steady. Zimmer posits a theory of sexual reproduction which explains it as a constant reshuffling of host-species' genes to keep pace with parasitic evolution. From this point of view, humans' incessant compulsion to mate is reminiscent of the non-survival behaviors of parasite hosts. Of course, reproduction is hardly a non-survival oriented activity; we only survive if we reproduce, but the question remains, why don't we just split in two like bacteria, or hermaphroditic creatures, giving new meaning to the expression, "Go fuck yourself"? The compulsion to sexually reproduce without resources to care for our young, with no concern about overpopulation, resulting in seven billion anxious and pessimistic humans plotting against each other, is clearly not the result of an intellectual process.
How about our longing for war? Note: I am not referring to delight at actually being in a war, but to the anticipatory delight at learning that the humdrum, boring and intolerable "peacetime" we've endured for so many years might finally come to an end, like the irrational delight felt by the comfortable English middle-classes at the outbreak of World War I described in Aldous Huxley's Point Counterpoint, and witnessed by Bertrand Russell as he mournfully watched excited young men boarding trains for the front. We might find it incredible that a fish would purposely float at the water's surface so a heron will eat it, yet our gullibility to war mongering is no less startling.
Our intellects are muffled and controlled by forces we can't see. These forces might emanate from parasites or transposons, or from our own kind. Maybe the next step in human evolution will be to truly elevate the intellect. Or maybe we will just float on the surface waiting for herons.