Equation 4 · Darwin's Finches: The Beak the Grants Measured for Forty Years
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the response: the amount the population’s mean should shift in the next generation, if the difference between survivors and non-survivors was genetic rather than purely environmental. Read the equation part by part below; each part has a contextual explanation and a link to its mathematical background.
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Symbol R
the response: the amount the population’s mean should shift in the next generation, if the difference between survivors and non-survivors was genetic rather than purely environmental.
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where S is the selection differential actually measured on the population in one generation, is the trait’s heritability, and R is the response: the amount the population’s mean should shift in the next generation, if the difference between survivors and non-survivors was genetic rather than purely environmental. Grant and Grant ran exactly this check on their own data, comparing the mean of a trait before a selection episode with the mean of the same trait in the following generation. The two independent beak traits, size and shape, evolved in the direction and close to the magnitude the equation predicted, with predicted and observed responses correlated at r = 0.832 across ten such…
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where S is the selection differential actually measured on the population in one generation, is the trait’s heritability, and R is the response: the amount the population’s mean should shift in the next generation, if the difference between survivors and non-survivors was genetic rather than purely environmental. Grant and Grant ran exactly this check on their own data, comparing the mean of a trait before a selection episode with the mean of the same trait in the following generation. The two independent beak traits, size and shape, evolved in the direction and close to the magnitude the equation predicted, with predicted and observed responses correlated at r = 0.832 across ten such episodes [ 2 ] . The equation is not a metaphor for what happened on Daphne Major. It is the arithmetic the team ran, in real time, against birds they had already caught and released.
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