A group buys its intelligence and its fragility with the same act of copying

A population gets smarter by copying and gets fragile by copying, and it is the exact same move both times. Joseph Henrich's finding is that humans dominate not as clever individuals but as relentless imitators: a two-and-a-half-year-old barely beats a chimp on raw information processing and buries it on social learning. We outsource what we know to the tribe, copying even the pointless stylistic tics of people we admire, mostly without noticing. That outsourcing is the secret of our success. It is also the machinery that lines an entire population up on one wager.

Because the instant everyone copies the same answer, independent error stops cancelling and starts compounding. When the 1980 dietary guidelines told America to pull fat and push sugar, the advice was not insane. The damage was the compliance. The whole country ran one substitution on one schedule, no subpopulation hedged the bet, and obesity did not drift upward, it spiked. The crowd that placed that wager is the same crowd whose copying makes us collectively intelligent in the first place.

So smart-aggregation and synchronized-ruin are not two risks to balance against each other. They are one purchase. Every increment of social-learning advantage is bought with an increment of correlated exposure, and the exchange rate does not negotiate. Decisions require ergodicity to succeed over time is the lone-actor version of the same bill; here the whole tribe pays it at once. You cannot turn up the dial that pools the group's knowledge without turning up the dial that can sink it on a single afternoon.

Source claim: The behavioral synchronization that makes a population collectively intelligent is the identical mechanism that makes it fragile, so a group cannot raise its social-learning advantage without buying an equal increase in correlated-failure risk.