In this chapter, we use an evolutionary lens to deepen understanding of maternal and family needs in the early postpartum period so that health care can be more aligned with confronted realities. The discussion is centered around the concept of the 4th trimester, which is the period between birth and the first 3 months postpartum. This framework encourages a holistic understanding of perinatal health by drawing attention to evolved maternal-infant needs. By addressing these ultimate-level contributors to health issues, we can facilitate more effective clinical support, comprehensive research, and a fuller “village” to enable new families to thrive. Core to this approach is the concept of trade-offs between parents and offspring, exemplified by lactation as a prime example of the complexities of dyadic needs and gap between the current culture of health and optimal support.