TY - JOUR T1 - Directional selection and the evolution of breeding date in birds JF - Science JO - Science SP - 798 LP - 799 DO - 10.1126/science.3363360 VL - 240 IS - 4853 AU - Price, T AU - Kirkpatrick, M AU - Arnold, SJ Y1 - 1988/05/06 UR - http://science.sciencemag.org/content/240/4853/798.abstract N2 - In many bird species, those pairs that breed earlier in the season have higher reproductive success than those that breed later. Since breeding date is known to be heritable, it is unclear why it does not evolve to an earlier time. Under assumptions outlined by Fisher, a model is developed that shows how breeding date may have considerable additive genetic variance, appear to be under directional selection, and yet not evolve. These results provide a general explanation for a persistent correlation of fitness with a variety of traits in natural populations. ER -