From the Universal Mind of the Pleistocene to the Distributed Intelligence of the Holocene: A Hypothesis of Cognitive Polarization in the Context of Gene–Culture Co-Evolution

The human brain has shrunk by approximately 10% over the past several millennia — yet this is not degeneration, but perhaps the greatest evolutionary optimization in our species' history. This preprint proposes the hypothesis of cognitive polarization: a macroevolutionary shift from the universal, all-purpose mind of the Pleistocene to the distributed, collective intelligence of the Holocene. Language emerged as the first exocortex, HAQERs provided the ancient genetic scaffold for domain-specific cognitive variability under balancing selection, the Neolithic transition created cultural niches that rewarded narrow specialization (hyper-systemizing, hyper-empathy), and generative AI (2023–2026) now completes the externalization of imagination itself. The individual brain is becoming a specialized node in a planetary superorganism. Neurodiversity — autism spectrum traits, savant abilities, extreme empathy — is not pathology, but evolutionary peaks essential for civilizational complexity. We are not losing reason. We are distributing it — across humans, cultures, and machines. We are becoming neurons in a vastly larger mind. The work integrates paleoneurology, ancient DNA, neurodiversity research, and contemporary AI into a unified evolutionary narrative. It offers four falsifiable predictions testable between 2026–2030, from virtual endocasting of fossils to longitudinal neuroimaging of heavy generative-AI users.