Costly Signaling
A signal is reliable only if it's costly to fake. Cheap talk can be produced by anyone regardless of quality; a costly signal can only be produced (sustainably) by those who genuinely have the underlying trait being signaled.
The Arabian babbler example: these birds compete to give food and assistance to others, even at personal cost. The behavior looks altruistic but is actually a dominance display — advertising "I'm so fit that I can afford to be generous." A weak bird can't sustain the cost.
Peacock tails are the canonical example: an elaborate, metabolically expensive tail signals genetic health. Only healthy peacocks can afford one. The waste is the point.
Costly signals in human behavior
- Art — time-intensive, cognitively demanding creative work signals surplus cognitive capacity (Geoffrey Miller's fitness-display theory)
- Education — years of costly credentialing signals intelligence and conscientiousness to employers (see signaling-theory-of-education)
- Religious observance — costly rituals (Hajj, fasting, tithing) signal sincere group commitment; free-riders can't easily fake them
- Charitable giving — visible generosity signals wealth and virtue (see competitive-altruism)
- Conspicuous consumption — expensive purchases signal wealth and taste (see conspicuous-consumption)
The key insight for institutions
Many institutions we think of as optimizing for stated goals (health, learning, helping others) are also — and sometimes primarily — mechanisms for expensive public commitments. The cost isn't a bug; it's what makes the signal legible.
This is why improving efficiency often fails to improve institutions: if you make the signal cheaper, it becomes less reliable, which undermines its social function even if it achieves the stated purpose better.
Related: hidden-motives social-brain-hypothesis conspicuous-consumption competitive-altruism