Why Do We Have Diversity in Physiological Function?

Department of Human Life Design and Science, Faculty of Design
NISHIMURA Takayuki, Associate Professor

 Humans exhibit diversity not only in appearance and form but also in physiological functions that respond to environmental changes and various stimuli. For example, some people are more sensitive to heat or cold, some have a higher or lower tolerance for alcohol, and others are more or less resilient to stress. These differences are often casually regarded as mere "individual differences," but in fact, human evolution and adaptation are often involved behind these variations. Our laboratory conducts research on human physiological diversity from an anthropological perspective of adaptation to the environment.

 This study focused on a genetic variant of the UCP1 gene, which is associated with obesity and believed to be linked to human cold adaptation. Previous research often suggested that certain genetic types were more prevalent in colder regions and thus related to cold adaptation. In contrast, this study estimated the genetic type of UCP1 associated with greater heat production during actual cold exposure and compared it with genetic data worldwide. The results showed that the frequency of this heat-generating UCP1 type was low in Africa, moderate in Asia, and high in Northern Europe. These findings provided strong physiological support for the traditional hypothesis that the UCP1 gene is related to cold adaptation. In other words, modern human obesity may partly be influenced by genetic adaptations to cold environments in our evolutionary past.

 This study focused on the relationship between bathing habits and thermoregulatory functions. Japanese people traditionally prefer soaking in a bathtub during bathing; however, in recent years, an increasing number of individuals only take showers. We measured physiological responses during bathing among two groups: those who soaked in a bathtub more than four times a week and those who did less than four times. The results revealed that individuals who frequently soaked in a bathtub exhibited a faster sweating response and a higher amount of sweat compared to those who did not. Blood flow responses showed similar trends. These findings indicate that frequent bath soakers possess superior heat-dissipation functions. Therefore, differences in bathing habits can influence human thermoregulatory functions. 

 From the above, the seemingly casual diversity in human physiological functions is influenced by a variety of factors, such as past adaptations to different environments and everyday lifestyle habits. Good design should fully understand such human characteristics and utilize these mechanisms to enrich, protect, and enhance human life in a healthy and safe manner.

Reference

Nishimura T, Katsumura T, Motoi M, Oota H, Watanuki S. Experimental evidence reveals the UCP1 genotype changes the oxygen consumption attributed to non-shivering thermogenesis in humans. Sci Rep. 2017 Jul 17;7(1):5570. doi: 10.1038/s41598-017-05766-3. 

■Contact
Department of Human Life Design and Science, Faculty of Design
NISHIMURA Takayuki, Associate Professor