Why do human females have permanent breasts? A new study reveals they may have evolved to keep babies warm, acting as a heat source to ensure infant survival.
Scientists might have uncovered the reason behind the permanently enlarged breasts in human females, a characteristic that distinguishes humans from nearly all other mammals. In most animals, including dogs and giraffes, females develop mammary glands solely for the purpose of feeding young and do not have persistent breast tissue. In contrast, humans have evolved large, noticeable breasts that remain throughout life, and for a long time, scientists have discussed why this unique trait developed.
A new study led by Dr Juho-Antti Junno from the University of Oulu suggests that the answer could be connected to keeping newborn babies warm. The research, published in Evolutionary Human Sciences, proposes that breasts may have evolved partly as a natural heat source to protect infants from cold conditions.
How Was the Study Conducted?
According to the researchers, human breasts stay at a relatively high temperature and provide a large surface area for skin-to-skin contact between mother and baby. This close contact could help transfer body heat more effectively, reducing the risk of hypothermia in newborns. This was especially important in early human history, when clothing and shelter were not available.
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To test this idea, the team studied 27 volunteers, including breastfeeding women, non-breastfeeding women, and men. These participants were placed in environments with three different temperatures, and thermal imaging cameras measured changes in chest temperature.
The results showed that breastfeeding women maintained warmer breast temperatures than the other groups and were more resistant to cooling conditions. On average, their breast temperature dropped only slightly compared to the larger drops observed in men and non-nursing women. This suggests that the breast may function as a stable heat source during breastfeeding.
Infant Survival
The researchers pointed out that the size and shape of human breasts create a larger contact area than a flat chest, allowing for more effective heat transfer during close holding. While breast size varies among individuals, the overall structure may have improved infant survival by providing both warmth and nutrition.
The team also emphasized that this theory does not fully explain all aspects of breast evolution, and more research, including studies on other primates such as chimpanzees, is necessary. Nonetheless, the findings offer a new evolutionary explanation for a uniquely human trait, showing how shared body heat may have once been essential in helping newborns survive.
