A new 'normal' body temperature

Body temperature decrease in remote populations in the Amazon show a decrease that took place over only 20 years

November 9, 2020

Have you taken your temperature recently? Was it lower than the standard 98.6 degrees Fahrenheit? 

Research published earlier this year indicates “normal” body temperature has been steadily decreasing in the United States over the last 200 years, now hovering around 97.8 degrees. Similar trends were reported in studies from the United Kingdom.  Thermometer Thermometer photograph courtesy of Unsplash. Download Full Image

New research not only found the same decrease in remote populations of people living in the Bolivian Amazon, but the decrease in body temperature took place over a mere 20 years.

The study was published by a transdisciplinary team, including Arizona State University anthropologist Benjamin Trumble. Their findings show rapidly decreasing body temperatures among the Tsimane people, living in remote communities in the rainforests of Bolivia.

“The finding of lower-than-expected body temperatures in the U.S. had a lot of people scratching their heads,” said study author Michael Gurven of the University of California, Santa Barbara. “Was this a fluke? Here, we confirm that body temperatures are below 98.6 degrees Fahrenheit outside of places like the U.S. and U.K. The area of Bolivia where the Tsimane live is rural and tropical with minimal public health infrastructure.” 

Researchers are unsure why the change in the Tsimane population body temperature is so rapid, but the Tsimane have undergone other rapid changes as well. Increased exposure to larger nearby market towns has impacted many facets of everyday life for the Tsimane. For example, some Tsimane communities close to the town San Borja now have access to electricity.

General societal advancements may point to why we’re seeing this trend. For example, in the U.S., body temperature started decreasing after the industrial revolution. Access to running water in people’s homes and increased availability of medical care could lessen the prevalence of infection and disease and cause body temperatures to decrease. 

Among the Tsimane, decreased body temperature could be a result of increased interactions with larger towns — leading to more antibiotic use, and better access to warm clothing and insulated housing. Changes in parasitic infection rates may also affect body temperature. Trumble notes there is no “silver bullet,” or one factor to which the decrease can be attributed. 

Other factors that may impact body temperature in the Tsimane are changes in body fat percentage, physical activity and sleep patterns. 

These temperature studies could have major implications for global health. Our body temperature is easy to measure and can be used as an indicator of overall health. Both in the U.S. and in Tsimane communities, the decreased body temperature has coincided with increased life expectancy. 

Figure Showing Body Temperature_Gurven Et All_Benjamin Trumble_ Science Advances_ASU Now_Tsimane Body Temperature

Figures showing predicted body temperatures by study date. From Gurven et al., Science Advances 28 Oct 2020: Vol. 6, no. 44, eabc6599 DOI: 10.1126/sciadv.abc6599. This work is licensed under CC BY-NC (http://creativecommons.org/licenses/by-nc/4.0/).

Expanding medical data

Trumble notes the majority of our medical data comes from studies conducted in the U.S. or Europe. This information forms our foundation of what is considered “normal,” but for most of human history, we lived in a nonindustrial environment.  

“If you compress the last 5 million years of human evolution into a single year, we were hunter-gatherers on Jan. 1, March 1 and so on, all the way until Dec. 31 at 11:40 p.m.,” Trumble said. “That’s when the industrial revolution happened.”

Human evolution provides important context in studying human physiology and changes in health over time and in our current populations. By better understanding health in nonindustrialized populations, researchers can achieve a broader view of how humans interact with and adapt to their surroundings, and better understand variation in global health.

“Right now, we’re operating way outside of the manufacturer’s recommended usage,” Trumble said. “Meaning, our bodies didn’t evolve to sit in chairs in front of computers.” 

Tsimane Health and Life History Project

The Tsimane live in about 95 communities in remote, forested locations in Bolivia, largely living off hunting and foraging. Few communities have access to electricity but none have access to running water.  

The Tsimane Health and Life History Project was founded 16 years ago. The team has received funding from the National Institutes of Health to study healthy aging, specifically cardiovascular health and Alzheimer’s disease. This team is composed of a mobile medical team of Bolivian doctors, a Bolivian biochemist and Tsimane community members trained as anthropologists. This group of experts provides free health care to the Tsimane, and, with approval from community members, conducts specific health-related studies. Research is largely led by co-directors Hillard Kaplan, Gurven, Trumble and Jon Stieglitz.  

The research, “Rapidly declining body temperature in a tropical human population” is published in Science Advances. 

Taylor Woods

Communications program coordinator, School of Human Evolution and Social Change


15-year-old student is beginning her college journey at ASU

November 9, 2020

Although she’s just 15 years old, Arizona native Carly Cairns chose to spend her first few months after graduating high school studying ancient Greek and Latin at Arizona State University. She’s currently enrolled as a nondegree student as part of a gap year before she officially begins her college career in fall 2021 at the University of Chicago. 

Cairns said her decision to dive into language classes through the School of International Letters and Cultures, even though they won’t count as academic credits toward her future degree, was fueled by her passion for lifelong learning. 
 Nondegree ASU student Carly Cairns smiles for the camera. She is wearing white pants, a black shirt, and black blazer with narrow vertical white stripes. She has long brown hair and is wearing makeup. Arizona native Carly Cairns is taking ancient Greek and Latin courses at ASU as part of a gap year before transferring to the University of Chicago. But Cairns is a little different from your typical nondegree student — she is just 15 years old. Download Full Image

“Every experience is unique to the person, and it just comes down to what your priorities are. For me, that was academic challenge. For others, it may be a robust social scene, or a strong athletic culture,” Cairns said. “Everyone’s academic journey comes in all shapes and sizes." 

Her journey began at age 10, when she enrolled in the Gary K. Herberger Young Scholars Academy, based on ASU’s West campus. Cairns advanced through the school’s Middle Years curriculum in just one year, moving on to the Cambridge IGCSE coursework at age 11 and the A-level program after that. In the process, she became the youngest student in the U.S. to receive a Cambridge AICE Diploma, though that was never her goal. 

“I hadn’t really sought to finish at a young age. I was just seeking a challenge and a good fit,” Cairns said. 

After graduating from the Herberger Young Scholars Academy in May just weeks after her 15th birthday and being named class valedictorian, Cairns resumed her ASU studies as a nondegree seeking student in the Zoom classrooms of Paul Arena and Sarah Bolmarcich, both lecturers in classics.

In Bolmarcich’s elementary ancient Greek class, students learn elements of ancient Greek grammar and apply their skills to read ancient Greek texts. Bolmarcich said she’s taught high school students before who were 17 or 18, but never someone as young as Cairns or as advanced in their academic career.

“Carly's one of the best students in the class, meticulous in her work and often asking for extra tips on how best to learn difficult Greek constructions,” Bolmarcich said. She noted that Cairns’ young age provides her with a head start on many of her peers. “It gives her a few extra years in life to enjoy this most beautiful of languages!” 

Cairns credits the support system of her family for her success. She was raised by a single mother and also has a close relationship with her grandfather, a constitutional law professor. They have helped her continue to challenge herself academically. When she’s not busy with her studies, she enjoys watching action movies with her family as well as playing the guitar and piano and acting in theater productions. 

In the spring, Cairns plans to continue her Greek studies and tackle an online writing class to better prepare her for her undergraduate coursework. After her year at ASU, she’ll pick back up at the University of Chicago, a school she chose for its rigorous curriculum and strong focus on the liberal arts. She’s also excited to move across the country and experience a new environment, though she’s a little familiar with the city already thanks to a summer program at Northwestern University. 

Cairns' current academic interests include history, democracy, criminal justice and constitutional law. She hopes to attend law school some day and her dream job would be to serve as a federal prosecutor for the Southern District of New York, which would put her at the forefront of some of the country’s most important cases. 

But all that is a few years in the future, though at her learning pace, perhaps not as far off as some might think. In the meantime, Cairns has third-declension Greek nouns to worry about, and she knows she might adjust her path as she discovers new academic passions. 

“I am prone to changing my mind often,” she said. “I think a broad liberal arts undergraduate experience will help me to explore and refine my interests. It’s exciting, really, and I definitely have time on my side.”

Kimberly Koerth

Content Writer, School of International Letters and Cultures