How strong is natural selection?

The strength of selection in nature has long been a controversial subject, partly because there were few quantitative measurements of phenotypic selec tion available until recently. In a new paper, Kingsolver and colleagues re viewed 63 studies and found that the median standardized directional select ion gradient (a measure of the strength of phenotypic selection) was 0.16. Whether this means selection in nature is strong or weak depends both on on e's point of view and on the error in selection estimates.