A small Finnish study has examined how breast tissue responds to temperature changes, comparing nursing women with non-breastfeeding women and men to explore a potential evolutionary function for permanent breast tissue. The researchers found that breastfeeding women tended to have higher breast surface temperatures and greater resilience to cooling, prompting discussion about a possible role in supporting infant warmth. The work was published in Evolutionary Human Sciences.
The study recruited eight currently breastfeeding women, twelve non-breastfeeding women and seven men, all aged 20 to 40. The age range was chosen to represent typical nursing ages while excluding puberty and menopause.
Participants were placed in a climatic chamber and exposed to three temperatures: 32°C, 27°C and 18°C. The researchers recorded breast surface temperature using thermal imaging at three points: the start, after ten minutes, and at the end of a 20-minute exposure. They described 27°C as a thermoneutral temperature for humans, representing a climate where energy expenditure for maintaining core temperature is minimised.
Results showed that breastfeeding women exhibited higher breast surface temperatures on average and demonstrated more resistance to cooling during the 18°C exposure. Specifically, breast surface temperatures dropped by an average of 2.5°C in the nursing group, compared with larger declines of 4.3°C and 4.7°C in the other groups.
“This proof-of-concept study clearly indicated the potential of the nursing women’s breasts to support infant’s thermal balance,” the authors state, highlighting a possible evolutionary mechanism linked to early human development and thermoregulation.
The authors caution that the study involved a very small sample, particularly among breastfeeding women, and that larger studies would be needed to confirm the findings. They note that the research contributes to the broader discussion of the evolutionary roles of human breasts, especially in the context of infants’ substantial thermoregulatory needs linked to encephalization.
The paper, titled Infant’s thermal balance and the evolution of the human breast – a proof-of-concept study, was authored by Tiina Kuvaja, Tiina Väre, Sirkka Rissanen, Hannu Rintamäki, Petri Lehenkari and Juho-Antti Junno.
