Birth-canal constraints halted brain expansion and forced postbirth growth tricks

Evidence

This expansion was finally halted about 200,000 years ago, probably by the challenges of giving birth to babies with increasingly bulbous heads. In most species, the birth canal is larger than the newborn’s head, but not in humans. Infant skulls have to remain unfused in order to squeeze through the birth canal in a manner that isn’t seen in other species. It seems our brains only ceased expanding because we hit the stops set by our primate body plan; if babies’ heads got any bigger, they wouldn’t be able to squeeze out of mom at birth. Along the way, natural selection came up with numerous tricks to circumvent this big-headed baby problem , including intense cortical folding, high-density interconnections (which permit our brains to hold more information without getting bigger) and a rapid postbirth expansion. Specifically, newborn human brains continue expanding at the faster prebirth gestational rate for the first year, eventually tripling in size. By contrast, newborn primate brains grow more slowly after birth, eventually only doubling in size. — Joseph Henrich, The Secret of Our Success, 213

Categorization

• XREF: connects to: Brain growth continues fifteen years after birth through self-formation — Catherine Malabou, What Should We Do with Our Brain?, 71; Sensory stimuli after birth directly shape brain connection volume and maturation — Catherine Malabou, What Should We Do with Our Brain?, 77; Brain expansion via longer lifespans makes species extinction-prone — Joseph Henrich, The Secret of Our Success: How Culture…, 977 (+3 more)

Broader Connections

• Brain growth continues fifteen years after birth through self-formation #expands (0.88) — Catherine Malabou, What Should We Do with Our Brain?, 71
• Sensory stimuli after birth directly shape brain connection volume and maturation #expands (0.78) — Catherine Malabou, What Should We Do with Our Brain?, 77
• Culture-driven cooking let natural selection shrink gut tissue to fund bigger brains #qualifies (0.76) — Joseph Henrich, The Secret of Our Success, 233
• Brain delocalization is constrained by embryonic connective organization #qualifies (0.75) — Catherine Malabou, What Should We Do with Our Brain?, 20
• Brain expansion via longer lifespans makes species extinction-prone #qualifies (0.72) — Joseph Henrich, The Secret of Our Success, 977
• Brain plasticity is a third term beyond genetic chance and necessity #qualifies (0.72) — Catherine Malabou, What Should We Do with Our Brain?, 47