The Prediction of Adaptive Evolution: Empirical Application of the Secondary Theorem of Selection and Comparison to the Breeder’s Equation

Despite strong selection pressures favoring larger body size, Soay sheep on St. Kilda are not evolving to increase in size, contrary to predictions from the breeder's equation (BE). This discrepancy suggests that unmeasured factors may be inflating estimates of phenotypic selection. Researchers applied both the BE and Robertson's secondary theorem of selection (STS) to analyze four morphological traits in Soay sheep, finding that while the BE predicted increasing size, the STS did not. The study highlights a potential general issue with naive evolutionary predictions in natural populations and suggests the STS as a tool to address this problem.

Morrissey, M. B., Parker, D. J., Korsten, P., Pemberton, J. M., Kruuk, L. E. B., & Wilson, A. J. (2012). THE PREDICTION OF ADAPTIVE EVOLUTION: EMPIRICAL APPLICATION OF THE SECONDARY THEOREM OF SELECTION AND COMPARISON TO THE BREEDER’S EQUATION. Evolution, 66(8), 2399–2410. https://doi.org/10.1111/j.1558-5646.2012.01632.x