Despite apparent episodes of food shortage, disease, violence, and severe weather conditions, it seems that, at least for some people, life in Chile between 500-1500 years ago was not that stressful. Lower than expected cortisol levels found in mummies’ hair have led researchers to suggest that some of the pre-Hispanic natives actually weren’t too anxious. These researchers found similar low levels of cortisol in a sample of modern Chileans. Could it be that the relaxed take on life has been pᴀssed on?

Scientific American reports that researchers from the University of Chile took hair samples from 19 mummies of San Pedro de Atacama in the north of Chile. Five of the mummies were from the Middle Period (400 to 1000 AD) and the rest from the Late Intermediate Period (1000 to 1400 AD). The researchers measured the capillary concentration of cortisol, “a hormone released in response to real or perceived threats.”

Location of the sites analyzed in the recent study. (López Barrales et al)

Hair grows at a rate of about one centimeter per month and this research is believed to provide an insight into stress levels during the last months of the individuals lives. Hermann Niemeyer, head of the Laboratory of Organic Chemistry at the Faculty of Sciences of the University of Chile and one of the researchers, told Scientific American that their results are “different from what had been ᴀssumed so far” about stress in pre-Hispanic South America.

This is not to say that the team’s analysis is fail proof. As Matías Loewy, a Scientific American reporter wrote in his article, there could be “some degree of degradation caused by decomposition”. But in response to this concern, Niemeyer said that “the mummies’ hair and other organic remains are extremely well preserved because of the arid San Pedro de Atacama atmosphere […] And cortisol itself is a fairly stable molecule.”

Hair from one of the oldest mummies studied at the Coyo East site, near San Pedro de Atacama in Chile. (IIAM-Catholic University of the North (UCN))

Another warning against generalizing their data to other pre-Hispanic communities is the low sample size. Lourdes Marquez Morfin, a bioarchaeologist and expert in ancient society and health at the National School of Anthropology and (ENAH) in Mexico, noted this drawback as well. She did, however applaud the application of new techniques to find out this kind of information.

The current research goes against previous results on high-stress being linked to harsh conditions for pre-Hispanic peoples who lived in and around the Andes region. Emily Webb and other researchers from the University of Western used similar methods in 2009 on a group of mummies found in Peru and reported elevated stress levels. They ᴀssociated their results with harsh life conditions that are believed to have been similar to those experienced by the Chilean mummies during their lifetime.

The team of researchers do warn that their results are not necessarily applicable to surrounding communities from the same time period. As the study’s lead author, Rocío López Barrales – a physical anthropologist from the University of Chile, said “The diversity of environments and cultural processes along the Andes is so heterogeneous that we must be cautious in expanding our findings to other prehistoric societies in our continent.”

A replica of the Plomo mummy on display at the Museo Nacional de Historia Natural in Santiago, Chile. (Jason Quinn/CC BY SA 3.0) The Plomo mummy was believed to be a child who was sacrificed.

The results of the current study may also be examples of individuals who were more “psychologically resilient” than others in their own communities. Feder, Nestler, and Charney define resilience as “a person’s ability to adapt successfully to acute stress, trauma or more chronic forms of adversity.” Individuals with higher psychological resilience are said to be more “stress resistant” than others.

Cortisol and resilience are connected by the fact that “Resilience is ᴀssociated with the capacity to constrain stress-induced increases in CRH [Corticotropin-releasing hormone – released by the hypothalamus in response to stress] and cortisol through an elaborate negative feedback system.” Thus, individuals who are more psychologically resilient also tend to have lower levels of cortisol as their bodies can better manage the system that releases cortisol – stopping the overproduction of the hormone.

With this in mind, it is interesting to point out that the current study also compared the data from their “less-stressed” mummies to the modern population and made a surprising discovery. According to Scientific American, the researchers found “the concentration of cortisol in the hair of 19 healthy, non-obese living residents of Santiago de Chile, ranging from 23 to 55 years old were similar in modern and in prehistoric samples.”

“While the environmental, technological and health conditions in ancient times could be considered restrictive in relation to the conditions of life today, apparently they did not alter the levels of systemic stress of these populations,” the authors wrote in Chungara, Revista de Antropología Chilena. While this is another small sample size, it does raise an interesting question: Could psychological resilience/a higher tolerance to stress pᴀss from one generation to the next?

One final point that should be taken into account is a need to guard against projecting modern views across cultures and time. Although most people would agree that a lack of food, disease, violence, and strong environmental changes would take a toll on their psychological wellbeing, there is a (slim?) chance that these aspects may not always be seen as hardships, but just a way of life. Humans can and have adapted to a variety of life conditions, who’s to say that everyone has to look upon their personal situation in the same way?

Although the current study of cortisol levels in the pre-Hispanic Chilean mummies’ hair does have some aspects that need to be worked out if it is to be applied to future studies, it still provides some out-of-the-box thinking about how researchers can go about identifying psychological health in the past. It also raises exciting questions about biological memories and the possibilities of cross-generational and intracultural personality traits of ancient societies.

Top Image: A mummy unearthed in the Atacama Desert. (Eigenes Werk / Anagoria/CC BY 3.0.de) and a mummy on display at Le Paige Museum, Atacama, Chile. (Patagonia SouthernLand Expeditions)