Equation 14 · Part 1 · The Peacock Problem: Darwin's Second Theory and Its Hard Tests

Symbol bar t

\bar t

\bar t

What this part means

the population mean of a male display trait and $\bar p$ the population mean of the corresponding female preference.

Its job in the formula

bar t is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.

Full expressionSymbol bar tArticle meaning

Where the article explains it

Let $\bar t$ be the population mean of a male display trait and $\bar p$ the population mean of the corresponding female preference; write $\beta_t$ and $\beta_p$ for the direct selection gradients acting on each (natural selection pulling $\beta_t$ downward, since the ornament is costly), $h_t^2$ and $h_p^2$ for their heritabilities, and B for the genetic covariance that non-random mating builds between the two traits.

The passage around this formula

…through the genetic covariance the mating system itself has created. When B is large enough relative to the stabilising pull of $\beta_t$ , the two equations no longer settle to a fixed point; they feed each other, and $\bar t$ and $\bar p$ escalate together until some external limit — a wing that can no longer lift the tail, a display that finally costs more than it wins — brings the pair to a halt. Nothing in the equations names where that limit falls. That absence of an internal stopping rule is the entire content…

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A variable is a named place for a value. Its letter is a local label: x can mean position in one formula and a data point in another.

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Sources cited in the article section

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