The Measurement of the Direct and Indirect Intensities of Natural Selection

  • Roger W. Doyle
  • Ransom A. Myers
Conference paper
Part of the Proceedings in Life Sciences book series (LIFE SCIENCES)


The intensity of selection on a trait is measured by (or defined by) the effect that the trait has on fitness. Major components of fitness, such as fecundity, will always be selected in a positive direction (Falconer 1960) when the traits are considered in isolation, with other traits held constant. It is obvious, however, that other traits will rarely be constant in populations of real animals. Most traits, especially such composite life history variables as survival and fecundity, are likely to affect fitness in a number of different ways, simply because they do not vary independently in their phenotypic expression. For example, low- and high-fecundity phenotypes may mature at different ages or show differential survival. Correlation of traits at the level of the phenotype is the net result of genetic correlation (pleiotropism, linkage) and environmental variation that influences two or more traits simultaneously (Falconer 1960).


Life History Trait Path Coefficient Phenotypic Correlation Reproductive Effort Selection Intensity 
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Copyright information

© Springer-Verlag New York Inc. 1982

Authors and Affiliations

  • Roger W. Doyle
  • Ransom A. Myers
    • 1
  1. 1.Department of BiologyDalhousie UniversityHalifaxCanada

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