Current age-based breastfeeding recommendations are supported by ample evidence and improve maternal and infant health. However, mixed-feeding trajectories – from complementary feeding introduction to full weaning – vary widely across populations. While numerous sociocultural factors influence this variation, comparative primate and human biological and cultural evidence also suggests that flexible mixed-feeding may be a human evolutionary norm. Durations of exclusive and total breastfeeding are expected to vary with infant energetic needs and maternal time, physical, and reproductive constraints. This perspective does not challenge current recommendations, but advocates for parallel dialogs about individually optimal mixed-feeding trajectories among families and health care providers.