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.
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?
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.
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?
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.
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.
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?
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.
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.