Fitness Indicators
Fitness indicators are traits that reliably signal genetic quality to potential mates because they are costly to produce and hard to fake. The theoretical basis is Amotz Zahavi’s handicap principle (1975): a signal can only be evolutionarily stable if cheaters cannot easily mimic it.
Primary source: miller-2001-mating-mind
The Logic
A peacock with a large tail suffers survival costs (slower escape, more visible to predators, higher metabolic demand). Only a peacock with genuinely good genes can afford to maintain such a costly ornament. Therefore, the tail reliably advertises genetic fitness — choosy peahens who select large tails produce offspring with better genes. The costly display is an honest signal precisely because it imposes real costs on low-quality individuals who cannot maintain it.
Physical vs. Mental Fitness Indicators
geoffrey-miller applies the same logic to human cognitive capacities:
| Trait | Cost | What it signals |
|---|---|---|
| Waist-hip ratio, bilateral symmetry | Developmental stability | Disease resistance, mutation-free genome |
| General intelligence (g factor) | Metabolic cost of large brain | Overall developmental stability; mutation load |
| Artistic skill | Time, energy, fine motor control | Creativity, sustained attention, hand-brain coordination |
| Verbal creativity | Processing speed, memory | Neurological quality |
| Consistent humour | Real-time cognitive processing | Mental agility, social calibration |
| Moral virtue (altruism) | Direct resource cost | Quality of character; cooperation potential |
Relationship to runaway-selection
The two mechanisms for sexual selection — runaway (Fisher) and fitness indicators (Zahavi) — were historically seen as competing explanations but may both operate simultaneously. Runaway can initiate a preference; fitness indicators can stabilise it by making the trait reliably informative.
Related Concepts
- sexual-selection — the broader evolutionary mechanism
- runaway-selection — the Fisher process, complementary to fitness indicators
- evolutionary-psychology — the field applying these concepts to human behaviour