Brain expansion via longer lifespans makes species extinction-prone

Evidence

The problem is that species who push this too far are more likely to go extinct when droughts, diseases, floods, or famines—shocks—hit that increase adult mortality rates, because the population can’t recover fast enough from the shock. For example, if females need to live to an average age of 30 years for a population to reproduce itself and a drought suddenly pushes the average age of death down to 20 years, the population will start shrinking and may disappear entirely. So, as natural selection pushes brain sizes up to increase individual fitness, it makes the species more vulnerable to extinction from shocks. This sets a limit to how far natural selection can increase brain sizes by reallocating a mother’s efforts and extending her life. Modern apes are probably up against this limit. — Joseph Henrich, The Secret of Our Success, 977

Categorization

• XREF: Pays off the ch12 claim on long postreproductive lifespans evolved for cultural transmission, adding a cost-and-extinction limit to that account. — connects to: Bigger-brained species evolve longer childhoods to permit learning — Joseph Henrich, The Secret of Our Success: How Culture…, 957; Birth-canal constraints halted brain expansion and forced postbirth growth tricks — Joseph Henrich, The Secret of Our Success: How Culture…, 213; Human brains tripled in size mostly within the last two million years — Joseph Henrich, The Secret of Our Success: How Culture…, 212 (+1 more)