Current theory in sexual selection is extended to predict within-sex variability with regard to selectivity towards mates in different mating systems. Generally, the sex that invests more in the care of each offspring should be more selective of mates than the sex investing less. Within each sex, individuals of low male quality should be less selective than individuals of high quality, but there should be less variation in selectivity among individuals of the sex investing more. When only one sex contributes parental care, however, individuals of that sex should be uniformly selective, while the other sex is expected to mate indiscriminately. Using feral pigeons (Columba livia), these hypotheses are tested for the case in which both sexes contribute substantial parental care, but in which females contribute more than males. As predicted, females were found to be more selective of mates than males were. On certain criteria, males of lower quality were less selective of mates than males of higher quality.
