Research regarding the affective experiences of stepparents is sparse. This study investigated the relationship between parental type (step or biological) and parental socioemotional investment, resentment, and jealousy. The study explored whether evolutionary or socialization accounts of parenting were able to explain the differential treatment of step and biological children. The pattern of findings-that stepparents generally exhibit lower parental socioemotional investment and higher parental resentment and parental jealousy than biological parents-suggests that stepparental antagonism might be due to differences in innate motivations of step and biological parents. Implications for research, theory, and practice are discussed.