Most research on parenting has focused on dyadic parent-child interactions to the neglect of triadic interactions between mother, father and child. Drawing from an evolutionary perspective, the present study examined how parental warmth and investment change as a function of the other parent's presence. Our sample consisted of 87 two-parent Dutch families raising firstborn preschoolers (44 boys, 43 girls; 36 months old). Parental warmth and investment were measured based on video recordings of structured and unstructured dyadic (mother-child, father-child) and triadic (father-mother-child) play sessions conducted in the families' homes. Results indicated that while mothers' warmth and investment did not change as a function of fathers' presence, fathers withdrew care in the presence of mothers. However, when mothers were away, fathers raised their level of care to that of mothers thus compensating for maternal absence. (Contains 1 figure.)