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Climate-induced Stress

Author Biographies

Cynthia M. Beall PhD, is a physical anthropologist at Case Western Reserve University, whose special interests are human growth and development, aging, human adaptability and medical ecology.  She previously conducted research on growth and development and infant morbidity/mortality in Andean populations, high altitude hypoxia and aging in Nepal and Bolivia and physical activity, physical fitness and aging in Nepal.  Her current research in Tibet is on high-altitude human adaptability and aging and diet.  Dr. Beall is a member of the U.S. National Academy of Sciences and she is the Co-Director for the Center on Research for Tibet.

 

Nina G. Jablonski is Distinguished Professor of Anthropology at The Pennsylvania State University.  A biological anthropologist and paleobiologist, she studies the evolution of adaptations to the environment in Old World primates including humans.  Her research is focused in two major areas: the evolutionary history of Old World monkeys, and on the evolution of human skin and skin pigmentation, and includes an active field project examining the relationship between skin pigmentation and vitamin D production.  Jablonski is currently involved in the development of new approaches to evolution education in the United States, including the development of a new "genetics and genealogy" curriculum for middle school students.  At Penn State, she directs the newly formed cross-college Center for the Study of Human Diversity, Evolution, and Behavior.

 

Albert Theodore Steegmann, Jr. is a retired Professor of Anthropology at the State University of New York, Buffalo.  Steegmann’s work includes: Human adaptation to stressful environments (cold, under-nutrition, heavy work, toxins); Craniofacial morphology, plasticity, variation and physiology; Response of body height and shape to past environmental change.  Steegmann held positions with the Human Biology Council, the American Association of Physical Anthropologists, and was the Chairman of Anthropology in the American Association for the Advancement of Science until his retirement.

 

Intro

The Earth's climate stresses the human body in various ways.  Our responses to these stressors are a complex and little understood mixture of genetics and   This chapter described how populations have adapted to temperature, ultraviolet radiation, and altitude. What are some other climate extremes that we have had to adapt to?

 

Cold

Humans have a long history of working and living in extremely cold environments, but even the most acclimatized people show a decrease in mental and physical performance when exposed to extreme cold. Thermoregulation is one of the most important factors of keeping your core temperature within a range that will support life.  In a resting state, some of your best defenses against the cold are muscle mass, subcutaneous fat, and previous exposure (acclimatization).   A European-American is genetically more adapted to the cold than an African-American, especially if they grew up in the north since CIVD shows low heritability.  Acclimatization begins to happen after 5-10 days, and is more important than life-long but less harsh exposure.

Thermoregulation
Thermoregulation

It is rare for a healthy, well-equipped person to die or suffer serious injury from the cold. However, cold is historically a major factor in casualties during war.  The trench warfare and lack of waterproof clothing during World War I created a perfect situation for cold-injuries.  Age, smoking, rank, previous injury, and race are all factors in susceptibility to cold injury.  The WWI and Korean War studies are interesting because there were so many casualties due to cold.

In the Korean war study, African-Americans from colder areas were still more likely than European-Americans from warmer areas to suffer from cold-injury. Why were the African-Americans (even from the north) not more acclimatized to the cold? Do genes play a larger role than acclimatization? If so, how do you explain the CIVD studies that showed low heritability?

Asia's Climate
This should be compared to the map in Human Biology by Stinson et al. page 194

Laborers in South China seemed to have a slightly better resistance to finger-cooling than South Japanese students, even though the laborers work in a warmer environment than the one where the students live.  I thought this was interesting, because it shows how people who stay indoors most of the time do not acclimatize to cold.  This means that while at one point natural selection for cold resistance was acting on human populations, it most likely no longer is.  The exception to that are people that still live their traditional lands using their traditional ways.

This is a ribbon seal, and example of what Native Arctic tribes might eat.
This is a ribbon seal, and example of what Native Arctic tribes might eat.

I thought the mention of a greater range of daily temperatures affecting mortality rates was interesting.  Cardiovascular deaths showed a positive correlation with temperature ranges, regardless of whether it was a warm or cold day.

Bergmann's and Allen's rules both essentially say that very cold environments lead to wider people with a smaller surface area to mass ratio and shorter limbs.  This would be supported if we found that people in the tropics tend to be more slender as a result of heat stress, but there is speculation that it is the result of undernutrition.

 

Heat

Humans can tolerate less increase in core temperature than decrease.  If you've ever had a very high fever, you know how uncomfortable just a few degrees can make you.  We cool ourselves pretty much opposite of how we keep ourselves warm - vasodilation.  This allows warm blood to move to cooler areas of the body.  People ill-adapted to  heat suffer from falling blood pressure, low plasma volume, and pooling of blood in the extremities.  Someone who is heat acclimatized will begin to sweat sooner and will better know when to stop exercising.  Acclimatization to heat seems to be slower than to cold.  Beginning at 7 days, it can take 8 weeks before an individual is resistant to heat illness.  The heat causes mortality mainly in elderly or overly stressed individuals.  Protection from the sun and air movement are two of the most important defenses against heat stress.  What are some cultural ways of keeping cool not mentioned in the book?  

 

 UVR Exposure

Map shows skin color based on UV radiation and precipitation.
Map shows skin color based on UV radiation and precipitation.

Humans evolved in tropical latitudes before moving polewards.  Why there is such a large range of skin tone has long been a source of curiosity.  Humans evolved dark skin, probably to protect the folate that is so important in our bodies.   As we moved away from the tropics, we were less likely to get too much sun, and more likely to get not enough. The light skin characteristic of Europeans is due to our need for vitamin D.  Dark skin is not as reactive in terms of producing vitamin especially D as light skin, so in our modern day and age when people have moved away from their ancestral homes, people of African heritage are most at risk for rickets.

 

 

 

 

High-Altitude Hypoxia

Populations in high altitude areas have adapted to living with lower oxygen levels in different ways.  For example, Andean highlanders have higher hemoglobin levels while Tibetan highlanders have levels more similar to lowlanders.  natural selection has worked on two different loci in these populations.   Both populations have a higher lung capacity than lowlanders. Man in Tibet

Man in Tibet from National Geographic

8 thoughts on “Climate-induced Stress

  1. rebeccaleon

    I think it is really interesting to think about the fact that people who stay indoors more are less acclimatized to the cold/heat than those who live more traditional lifestyles and spend more time outside. I wonder if there is an acclimatization difference between Americans who are from the South and those who are from the North. The majority of Americans who live in the North do not have air conditioning, but most people living in the South do. So, even though you always hear about Southerners being more acclimatized to hot weather (because it gets hotter in the South) is that really the case when most of the time people in the South are in temperature controlled buildings? Is it possible that Northerners are better able to deal with the heat of their environment, because the time they spend indoors away from the heat outside is not usually systematically controlled? This would be interesting to study if it hasn't already been done.

    It has been proposed that the reason many people living in the tropics are slender due to lack of nutrition, but how would this explain that many people living in Africa who are slender are also tall? I have a hard time believing that people who are malnourished could wind up so tall. However, there has to be some way to explain the phenomenon that is known as Bergmann’s and Allen’s rule. It is interesting to note that many people living in Central American do not fit the stereotype of this rule (i.e., slender build with long limbs). Many people of Maya descent are very short and stocky, which contradicts this rule.

  2. Taylor Burbach

    I think she has a point. My grandmother lived her whole life in Alabama but has spent the greater majority of her life indoors, especially in that last 20-25 years. She has such a hard time handling the heat now, which is probably explainable in part by her age. I've also found it easier to handle the heat the more time I spend outside. I think this is something we know intuitively, but I've never thought about considering time indoors as something that affects acclimatization.

  3. mrhill2

    I personally have had to deal with this notion myself. When I first moved here from Ohio, I had to get uses to there not being a true fall or winter and the summers being really hot. I spend a lot of my time inside during the summer but I never thought to much of it past me just beating the heat, not acclimatization. But I also noticed when I first moved here that what is considered cold down here and what is cold up north is vastly different. So I can totally relate to the picture in the Heat section.

  4. Jonathan Belanich

    In response to Rebecca's remarks on the heat in the North, my family does have air conditioning, but maybe it gets used once or twice a year. But I think from personal experience that many more people get/use it than in the past, and many stores/restaurants/public places have air conditioning on most of the time. But still, in spite of this, I would think that Southerners are probably better suited to the heat. In 85+ weather I'm close to melting, whereas other people can actually be chilly.

    Could this be possibly due to heritage from the area? Most of my family is from Europe, and are only recent immigrants, whereas some families in the South can be in the same relative area for generations. Is it possible acclimatization could be epigenetically linked/passed on in some manner?

  5. Andrea Morris

    I'm also from up north and I too had a difficult time adjusting to the heat my first semester down here. It was even worse when I would go from the warm temperatures down here to the much cooler temperatures up in Illinois. I would often get sick as well after traveling from down here back up home. Especially during the winter when the average temperature is between 20 and 30 degrees. I assumed this would happen because my body wouldn't be able to adjust fast enough going from one extreme to the next. Has anyone else found themselves getting sick when they experience vast climate changes in a rapid period of time?

  6. Paula Adams

    I think that the acclimatization to cold is both genetic and adaptive. While where you grow up is super important, I think that there has to be a genetic component to this. Just in my family there are some people who get hot really easily and always wan the air conditioner on 65 degrees. But then there are some people who are always cold and want the heat on in the summer. Genes that contribute to this are probably very complicated, and it would be hard to track them. You would need to look at the genes associated with sweating, circulation, metabolism, and anything else that deals with body heat. All of these are complicated processes that would not be easy to find the genetics that are associated with it. The genes you have probably limit you to how fast you adjust to temperature, but the climate you grow up in determines where in your own genetic range you fall.

  7. Brittany Fuller

    I do not do well in the cold. I have lived in Alabama for most of my life. We did live in Germany for a while when I was younger so I would have thought that I would have been more adapted to the cold, but I am not. The guy that I dated for 3 years was from Wisconsin. We went and saw his family over Christmas for three years. I thought I was going to die from the cold. My feet would go numb when I had my ugg boots on if I was outside for too long. The whole time we were there I felt like I couldn't get warm. On the flip side to that he had a hard time adjusting to the warm weather here. He would wear shorts for most of the winter without it really bothering him. During the summer he hated the heat.

  8. Sophia Fazal

    I was born in the north, specifically Chicago, IL, but spent more than half of my life in Alabama. This idea of climate sensitivity became extremely apparent to me during my college career, when I came back down to the south to go to school at The University of Alabama.

    Particularly, this past Thanksgiving I went home from a lovely 60 degree day in Tuscaloosa, Alabama to a frigid 19 degree day in Chicago, IL. My less than a week at home felt like such a brutal storm, even though the sun was shining every single day. However, when I came back to Alabama I was shocked, I didn't feel cold at all anymore. Before going home, I was complaining about the weather to everyone, and all I ever heard in response was, "But you're from the north..."

    Well, I am from the north and I'm proud of it! When I finally returned home after break the weather felt great, and still does. I realized what my body had grown so accustomed too and why anything between 30-60 degrees really did feel like great weather.

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