Fisher's Principle
Updated 2026-08-01
INTRODUCTION
English translation pending.
CORE DEFINITION
Proposed by Ronald A. Fisher in The Genetical Theory of Natural Selection. If one sex is rarer, parents producing that sex gain more grandchildren on average, because their offspring face less competition for mates. Selection therefore pushes the sex ratio back toward equality, making parity an evolutionarily stable strategy. The argument assumes equal parental investment per offspring and applies to the population-level ratio, not to the preferences of individual parents.
SCAFFOLDING EFFECT
Reduce cognitive load
- Read markets: when a skill or asset becomes scarce, expect a premium that draws in new supply - Forecast reversion: treat extreme scarcity as temporary rather than as a durable advantage - Spot equilibrium: identify where returns are equalized because entry and exit are free
Anchor fast decisions
The payoff to producing a son or a daughter depends on how many others are producing the same sex. When one sex is rare, each of its members competes with fewer rivals for mates, so parents who produce it get more descendants per unit of investment. That advantage attracts more such births, which erodes the advantage until the two payoffs equalize, which happens exactly at parity.
MINIMUM ACTION
In progress 0/1Practice this model in one real situation:
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Source support: Explicit
- en.wikipedia.orghttps://en.wikipedia.org/wiki/Fisher's_principleverified
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