Evolutionary Rescue Race

Warming rate 0.045 °C/gen

Heritability h² 0.35

Selection tolerance ω 2.2 °C

Carrying capacity K 500

Generation

Population N

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Adaptive lag

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Mean fitness

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How it works

Each individual carries a heritable heat-tolerance trait. Every generation the climate optimum θ moves forward at the warming rate. Individuals whose trait sits near θ have high fitness; the population's mean fitness sets both its growth rate and, via the breeder's equation, how far the mean trait shifts toward θ next generation.

θ(t+1) = θ(t) + rate
W(x)   = exp(-(x-θ)² / 2ω²)
R      = h² · S          (breeder's equation)
μ(t+1) = μ(t) + R
N(t+1) ∝ N(t) · W̄(t), capped at K

Warming rate — climate velocity: how fast the optimum trait value moves each generation.
Heritability h² — the fraction of trait variance that is genetic; only that fraction responds to selection, so low h² means slow evolution even under strong selection.
Selection tolerance ω — how forgiving the fitness curve is; a narrow ω means individuals off-target die fast, punishing lag hard.
Carrying capacity K — sets population size, which sets how much demographic noise (drift) can derail a small, lagging population.

Real-world relevance: this lag between a moving climate optimum and a population's evolving mean trait is called evolutionary rescue when adaptation wins, and evolutionary suicide or extinction debt when the rate of environmental change outpaces the population's adaptive capacity — exactly the race described for physiological and phenological adaptation in the wild.

High-fitness individual Low-fitness individual Climate optimum θ Population mean μ

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