Human breasts may have evolved to regulate newborn body temperature, study reveals

A new study from the University of Oulu offers fresh insights into the evolutionary purpose of human breasts. Published in Evolutionary Human Sciences, the research suggests their shape and size may have developed to help regulate a newborn's body temperature. This finding challenges long-held assumptions about breast anatomy and its role beyond milk production alone.

The interdisciplinary team combined evolutionary theory with applied physiology to test their hypothesis. Under controlled conditions, they measured breast surface temperatures in breastfeeding mothers, non-lactating women, and men. Results showed that lactating breasts consistently maintained higher temperatures, suggesting a thermoregulatory function.

The study proposes that the human breast's expansive surface area during suckling enhances heat transfer to infants. This mechanism would help stabilise a newborn's body temperature, reducing the risk of hypothermia. Researchers introduced the thermal regulation hypothesis, arguing that breast prominence evolved to support neonatal survival through efficient skin-to-skin contact.

Traditionally, breast size has been viewed as unrelated to milk production. However, this work implies that anatomical features once considered purely aesthetic may serve critical biological roles. The findings also call for a broader re-examination of human adaptations, urging scientists to revisit even well-studied traits.

While the study does not yet recommend changes to clinical practices like kangaroo care, it underscores the need for further investigation. The authors highlight how evolutionary perspectives can reshape understanding of human anatomy and its functional complexity.

The research provides a new framework for interpreting breast evolution, linking their structure to neonatal thermoregulation. Clinicians, anthropologists, and biologists may now reconsider how anatomical traits contribute to survival. For now, the study serves as a starting point for deeper exploration rather than an immediate shift in medical guidelines.