The Crying Game

Evolutionary models of offspring solicitation systems have emphasized the potential for offspring manipulation of parents and the role of signal production costs in limiting exaggeration of need by offspring. Another, neglected possible evolutionary function of offspring solicitation is competition with siblings for access to limited parental resources via condition-dependent displays of probable offspring contributions to parental fitness. In this brief review of the behavioral ecological literature, I report that offspring phenotypic quality is indeed a common positive correlate of parental investment, and that apparently condition-dependent displays modulate differential parental investment. I argue that short-term fluctuations in need are secondary to intrinsic offspring phenotypic quality in determining parental investment responses to solicitation. I conclude that need display is an incomplete evolutionary explanation of offspring solicitation behaviors, and that fitness advertisement is a primary function of such neonatal behaviors. Offspring solicitation, like courtship displays and agonistic signals, may be best understood within the framework of competitive Zahavian signal selection. Future avenues of experimental research are proposed.