What if our intelligence—rather than being a divine spark or a marvelous work of nature (depending on whether one identifies with creationism or evolutionism)—were a tragic error in life’s evolutionary process, a “disadvantageous” path that nature happened to take and will soon abandon in order to return to forms of life less destructive to the environment? This question, as distressing as it is fundamental for all humankind, is what the theory set out in this essay—named “Cancrism” by its author—tries to answer. And the answer, unfortunately, is yes. Yes, our intelligence is the product of an abnormal evolution undergone by the brain of the genus Homo, an evolution that has allowed us to bend the very laws of nature to our advantage, to upset—again to our advantage—the delicate and ultra-complex system of biological devices and mechanisms that formed spontaneously over millions upon millions of years, and to do so in a flash, in just a few thousand years, a mere instant on the cosmic scale. But it does not enable us to create a new equilibrium as solid as the one we destroyed. Our intelligence (or reason) is indeed the most powerful instrument to have developed on this planet, but its power is nothing compared with what would be required to govern, in a stable and balanced way, the innumerable variables present in nature. By breaking an infinity of seemingly useless links, we have interrupted the vital flow of the super-organism that hosts us, and we now suffer the consequences, with their sadly familiar names: pollution, global warming, desertification, overpopulation, and so on. How can one fail to see a correspondence between this kind of behavior and that of cells whose genetic material mutates to the point of turning them into cancerous agents, unwilling to accept programmed cell death (apoptosis) and destined, through their uncontrolled proliferation, to set the tumor process in motion?