Joseph Henrich — Humans defeated smarter species with cultural evolution

Henrich treats the spread of one Eurasian population around 70,000 years ago as a puzzle precisely because the available genetic evidence does not point to an obvious leap in individual cognitive capacity. Neanderthals had larger brains, while the expanding population may even have been less capable at processing information individually. He therefore considers social organization and accumulated cultural knowledge as alternatives to a simple genetic explanation. The historical parallels he names, including the Bantu, Austronesian and Neolithic expansions, show that population replacement has recurred, but they do not by themselves establish what caused the much earlier Eurasian expansion.

The proposed advantage is a collective brain: institutions and links between communities can preserve complex techniques and move knowledge between people. Henrich uses Eurasia's size, east-west orientation, the so-called Lucky Latitudes, and later state bureaucracies to illustrate conditions that can connect populations. He also points to trade, intermarriage, shared rituals and periodic gatherings as ways information may travel. The examples are suggestive rather than a direct reconstruction of the 70,000-year-old event; Henrich explicitly says researchers do not know whether bows or another technology drove that expansion.

The discussion challenges explanations that treat one missing invention, such as the wheel in the Americas, as decisive. Henrich notes that Maya carts and toys did have wheels, and questions whether the absence of draft animals is enough to explain the broader pattern. His account instead emphasizes geography, population size, exchange routes, institutions and the accumulated ability to organize people. For the prehistoric expansion, he similarly favors a package: the Inuit had social practices that maintained connections, along with bows, dogs, sleds and coastal boats. Their Dorset rivals may have had better technology at some point, but dispersal and declining contact could also cause knowledge to be lost.

In this account, expansion and decline are recurring pulses rather than an uninterrupted march toward progress. Groups may copy useful practices from rivals, absorb migrants, or fight over territory; some lineages disappear, while others interbreed. Geography, language change and increasingly local marriage patterns can fragment networks, making previously shared knowledge harder to maintain. The examples establish plausible mechanisms, not a measured history of the ancient population in question, and Henrich leaves the specific trigger unresolved.

Henrich describes a bootstrapping problem: when little useful knowledge exists in a group, investing in social learning appears less valuable than solving problems alone; without social learning, however, accumulated culture remains limited. His proposed conditions for crossing that threshold include changing environments at an intermediate pace, tool-using ancestors who could live in large groups, and the greater chance that someone in a larger group would discover a useful practice. These are explanatory factors he draws from cultural-evolution theory, not a definitive account of why only the human lineage developed cumulative culture.

Henrich says evidence for exchange between groups reaches well into the Paleolithic: communities moved trade goods and sometimes exchanged genes. Ancient DNA also suggests a contrast relevant to the earlier expansion puzzle: European Neanderthals lived in very small groups, while the expanding populations appear to have been larger. In Henrich's framework, these groups therefore differed not only in ancestry but in the size of their connected knowledge networks. The evidence supports a population-size contrast; it does not specify the precise social practices or technologies that caused expansion.