Equation 2 · Fitness Landscapes and the Limits of the Metaphor
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Symbol w
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Symbol g_0
is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.
Symbol g_1
is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.
Symbol g_L
is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.
subscript
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The reason is an ordering constraint. Under the standard assumption that a population moves by fixing one beneficial mutation at a time, a mutational path is accessible only if fitness increases at every single step: . A single step that violates this inequality closes the entire path, regardless of how high the endpoint is. Sign epistasis is exactly the mechanism that produces such steps, and reciprocal sign epistasis — where each of two mutations is deleterious without the other and beneficial with it — is what creates genuinely separated local optima.
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