Human digestive organs are dramatically undersized for our body compared to other primates

Evidence

Compared to other primates, humans have an unusual digestive system. Starting at the top, our mouths, gapes, lips, and teeth are oddly small, and our lip muscles are weak. Our mouths are the size of a squirrel monkey’s, a species that weighs less than three pounds. Chimpanzees can open their mouths twice as wide as we can and hold substantial amounts of food compressed between their lips and large teeth. We also have puny jaw muscles that reach up only to just below our ears. Other primates’ jaw muscles stretch to the tops of their heads, where they sometimes even latch onto a bony central ridge. Our stomachs are small, having only a third of the surface area that we’d expect for a primate of our size, and our colons are too short, being only 60% of their expected mass. Our bodies are also poor at detoxifying wild foods. Overall, our guts—stomachs, small intestines, and colons—are much smaller than they ought to be for our overall body size. Compared to other primates, we lack a substantial amount of digestive power all the way down the line, from our mouth’s (in)ability to breakdown food to our colon’s capacity to process fiber. Interestingly, our small intestines are about the size they should be, an exception that we’ll account for below. — Joseph Henrich, The Secret of Our Success, 221

Categorization

• SHARE: A gorget of specific numbers (stomach at 1/3 surface area, colon at 60% mass, mouth at squirrel-monkey size) worth sharing with anyone into evolutionary physiology or paleoanthropology.
• XREF: This sets up the ‘cooked food / external processing’ argument that connects to the reader’s broader culture-as-adaptation framework (guts shrank because culture pre-processes food externally). — connects to: Cooking evolved culturally and reshaped human digestive anatomy and function — Joseph Henrich, The Secret of Our Success: How Culture…, 224; Culture-driven cooking let natural selection shrink gut tissue to fund bigger brains — Joseph Henrich, The Secret of Our Success: How Culture…, 233; The human prefrontal cortex is anatomically outsized compared to other primates and mammals — , The Rod and the Child: A Global History…, 5879 (+3 more)

Broader Connections

• Culture-driven cooking let natural selection shrink gut tissue to fund bigger brains #expands (0.90) — Joseph Henrich, The Secret of Our Success, 233
• Cooking evolved culturally and reshaped human digestive anatomy and function #expands (0.85) — Joseph Henrich, The Secret of Our Success, 224
• Cultural tools replaced anatomy, so natural selection weakened human bodies #expands (0.80) — Joseph Henrich, The Secret of Our Success, 235
• Culturally transmitted skills created selection pressures shaping human anatomy and physiology #expands (0.80) — Joseph Henrich, The Secret of Our Success, 313
• The human prefrontal cortex is anatomically outsized compared to other primates and mammals #complicates (0.78) — , The Rod and the Child, 5879
• Humans are biologically dependent on cooked food and cannot survive long without it #corroborates (0.75) — Joseph Henrich, The Secret of Our Success, 230