Social Brain Hypothesis

Also called the Machiavellian Intelligence Hypothesis. Human intelligence evolved primarily to navigate social competition — not to solve ecological challenges like hunting, tool use, or fire.

The distinction matters because:

Ecological explanations imply intelligence grew to help us cooperate against the environment. Flattering. Win-win narrative.
Social explanations imply intelligence grew to help us outcompete other humans. Unflattering. Zero-sum narrative.

Most researchers, for understandable reasons, spend more time looking under the ecological streetlamp. But the evidence points toward social competition.

The evidence

Brain size across primate species correlates with social group size, not ecological complexity. Species that live in larger, more politically complex groups have bigger relative brain sizes.
The cognitive demands of social life — tracking alliances, detecting cheaters, modeling others' beliefs, managing reputation — are higher than those of ecological challenges like foraging.
The pace of brain growth in hominid evolution was faster than ecological changes alone can explain.

What this implies

Our deepest cognitive machinery — theory of mind, language, deception detection, coalition tracking — evolved not for science or engineering but for political maneuvering in small groups. We're running savanna-politics software on industrial-civilization hardware.

This is the deep origin of hidden-motives: if intelligence evolved for social competition, then much of what we think and do is oriented toward competitive social goals, even when we think we're doing something else.

Sources

the-elephant-in-the-brain-kevin-simler-robin-hanson