Human irrationality is not new. It is not a modern disease of disinformation or a failure of education. It is older than writing, older than fire. Our ancestors survived because their minds were quick to take shortcuts: to leap at signs of danger, to cling to the safety of the tribe, to trust stories more than statistics. What saved them in the savannah now sabotages us in the city.
But in the 21st century, a shift has occurred. Our biological quirks have not changed; the environment around them has. Where once irrationality was bounded by the limits of the village, today it is amplified by global systems designed to exploit it. The tribal instinct has become the viral instinct.
Consider the economy of attention. Outrage travels faster than reason not because people are foolish, but because the brain is tuned to treat threat as urgent. A rustle in the grass could have been a predator; hesitation killed. On social media, that same reflex is captured and commodified. Anger and fear guarantee clicks, and clicks guarantee profit. What was once adaptive has been made addictive.
Repetition offers another example. Psychologists have shown that the mere act of hearing a claim repeatedly makes it feel more credible — the “illusory truth effect.” In small communities, repetition meant reinforcement of shared norms and wisdom. Online, repetition is weaponized: an algorithm shows the same claim a hundred times, and what was once a lie acquires the glow of common sense.
Artificial intelligence adds a further twist. Large language models generate fluent text without understanding, echoing our own tendency to prefer coherence over truth. They can fabricate authority at scale, reflecting our biases back to us in polished sentences. The result is not just misinformation but a new form of mimicry: machines reproducing the very irrational patterns evolution has carved into us.
None of this should make us fatalistic. If irrationality is ancient, the systems that exploit it are not. They are recent, fragile, and human-made. The lesson is not that the brain is broken, but that its vulnerabilities must be recognized and respected. Just as societies built sanitation once they understood disease, so too must they build cognitive guardrails once they understand bias.
The danger lies not in irrationality itself but in its industrialization. Our ancestors’ minds, designed for survival in scattered bands, are now entangled in feedback loops that no single brain can escape. To leave those loops unregulated is not liberty but manipulation.
The task ahead is philosophical as much as technical: to decide what it means to design systems that honor human limitation rather than exploit it. We cannot rewire the brain, but we can rewire the world it inhabits. That choice remains ours.
