By: Adam Ziegler, Matthew Papp, Shivam Gandhi, Nikolas Steege, Bio323 Evolution, Fall 2019, Stonehill College
Let’s face it, we all sweat. Despite sweat being such a common and prominent aspect of everyday life, not many people understand what causes sweating, or why not all mammals sweat. A recent paper explored the difference in human sweat compared to other primates from compiled data sets across three phylogenetic models. The research focused on the two glands that are primarily involved in sweating, the apocrine and eccrine glands. By combining glycogen concentration, climate, and distribution of glands, the authors were able to predict the eccrine gland ancestral relationship. The results show exactly how humans have come to evolve the current gland distribution and offer a previously unstudied insight into our ancestors.
In the 2018 Journal of Human Evolution article, the evolution of eccrine sweat glands in human and nonhuman primates, Dr. Kamilar and Mr. Best explored the difference in human sweat compared to other primates from compiled data sets across three phylogenetic models. This paper by Dr. Kamilar and Mr. Best compiles data from 41 different publications in 35 different species of primates. While many characteristics were studied in this paper, the three overarching characteristics were gland distribution, degree of capillarization, and glycogen concentration.
There are two types of glands involved in sweating in mammals: the apocrine gland and the eccrine gland. The apocrine glands secrete sweat from hair follicles while the eccrine glands are more efficient and secrete sweat directly onto the skin. Having eccrine glands on only the hands and feet is the ancestral trait for all primates. The apocrine and eccrine glands are essential to a primate’s ability to regulate its internal temperature. When looking at eccrine versus apocrine glands the two clades of primates that do not include humans have 0% eccrine glands on their general body surface. If we look at the clade including humans however, all the primates have at least around 50%, with gorillas and chimpanzees having around 75%, and humans having 100% eccrine glands.
The authors also viewed a few other factors that affect eccrine gland distribution such as capillarization, glycogen concentration, and climate. Capillarization is the creation and development of capillaries. Capillaries are the smallest blood vessels found in the body. When production of the formation of these capillaries is increased, more heat can be transferred into the body. Location of area can be an important factor in degree of capillarization. Locations that have hotter climates compared to colder climates have an increased development of capillaries as well as glycogen stores that result in more sweating.
Glycogen is a polysaccharide that is used in energy storage and regulates sweat and body temperature. Newer primate species had evolved to have the most glycogen concentration, while older primates had intermittent to low levels of glycogen concentration. Because these newer primates lived in warmer climates, the hotter and drier climates led to greater glycogen stores and the evolution of the eccrine glands/more sweating. We use glycogen to sweat and eventually deplete it, but primates don’t deplete their glycogen because they have become acclimated to the heat. Increased glycogen concentrations are an indicator of a species’ way of regulating their temperature.
Link to paper:
Best, A. & Kamilar, J. (2018). The evolution of eccrine sweat glands in human and nonhuman primates. Journal of Human Evolution, 117, 33-43. Retrieved from https://www.researchgate.net/publication/323399145_The_evolution_of_eccrine_sweat_glands_in_human_and_nonhuman_primates
Link to Twitter and Lab of Jason Kamilar: https://www.kamilarlab.org
Link for Image of guy sweating:
Demonstration of Sweat. Image credit: https://en.wikipedia.org/wiki/Perspiration#/media/File:Demonstration_of_Sweat.jpg by Dogbertio 14 is licensed under CC BY 3.0
Link for the song we used: