The Human Brain Has Been Shrinking for 30,000 Years. Nobody Knows Why

Why did human brains shrink? Thirty thousand years ago, the average human skull held about a coffee cup more brain than yours does, and the people carrying it built no cities, no writing and no wheel. Then the brain got smaller, and everything we're proud of came after. We follow five clues: a measuring jug of seed poured out of thousands of skulls, an ant colony whose workers' brains shrink as the colony grows, the Siberian foxes that grew floppy ears when bred only for calm, a tape measure that shows the body can't explain the drop, and a clay tablet that did the same job as the phone in your hand. And the honest twist: scientists are still fighting over when the shrink happened, and whether it happened at all. Chapters 0:00 More knowledge in one hand than anyone before 1990 1:19 Clue 1: The measuring cup 3:00 Clue 2: The ant 4:50 Clue 3: The dog (and the Siberian foxes) 7:11 Clue 4: The tape measure 8:16 Clue 5: The notebook (taxi drivers and satnav) 10:37 Where the experts split 12:04 Case closed Sources Hawks, J. (2011). Selection for smaller brain size in Holocene humans. arXiv:1102.5604. DeSilva, J. M., Traniello, J. F. A., Claxton, A. G. & Fannin, L. D. (2021). When and why did human brains decrease in size? A new change-point analysis and insights from brain evolution in ants. Frontiers in Ecology and Evolution, 9, 742639. Villmoare, B. & Grabowski, M. (2022). Did the transition to complex societies in the Holocene drive a reduction in brain size? A reassessment of the DeSilva et al. (2021) hypothesis. Frontiers in Ecology and Evolution, 10, 963568. DeSilva, J. M. et al. (2023). Human brains have shrunk: the questions are when and why. Frontiers in Ecology and Evolution, 11, 1191274. Stibel, J. M. (2021). Decreases in brain size and encephalization in anatomically modern humans. Brain, Behavior and Evolution, 96(2), 64–77. Cieri, R. L. et al. (2014). Craniofacial feminization, social tolerance, and the origins of behavioral modernity. Current Anthropology, 55(4), 419–443. Wilkins, A. S., Wrangham, R. W. & Fitch, W. T. (2014). The "domestication syndrome" in mammals: a unified explanation based on neural crest cell behavior and genetics. Genetics, 197(3), 795–808. Kruska, D. C. T. (2005). On the evolutionary significance of encephalization in some eutherian mammals. Brain, Behavior and Evolution, 65(2), 73–108. Trut, L. (1999). Early canid domestication: the farm-fox experiment. American Scientist, 87(2), 160–169. Maguire, E. A. et al. (2000). Navigation-related structural change in the hippocampi of taxi drivers. PNAS, 97(8), 4398–4403. Dahmani, L. & Bohbot, V. D. (2020). Habitual use of GPS negatively impacts spatial memory during self-guided navigation. Scientific Reports, 10, 6310. Pietschnig, J. & Voracek, M. (2015). One century of global IQ gains. Perspectives on Psychological Science, 10(3), 282–306. Hare, B. (2017). Survival of the friendliest: Homo sapiens evolved via selection for prosociality. Annual Review of Psychology, 68, 155–186. Narration is AI-generated (ElevenLabs). Illustrations are AI-generated from our own prompts. #AncientHumans #HumanEvolution #Archaeology