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The chapter this week was all about stress and reminded me of one of our very own professors here at University of Alabama, Dr. Dressler. His work on cultural consonance and its connection in African Americans in Alabama and higher blood pressure levels is actually mentioned in the chapter we read. The chapter discussed how blood pressure and depression are some of the responses that occur from stressors. The article I decided to look at was “Does perceived stress mediate the effect of cultural consonance on depression?” In the article the researchers, Mauro Balieiro, Manoel Antônio dos Santos, José Ernesto dos Santos, and William Dressler were interested to see “does stress appraisal, as measured by the PSS, mediate the effects of cultural consonance on depressive symptoms? (Balieiro, Antônio dos Santos, Ernesto dos Santos , Dressler, 2011: 532).”

In the article, the study takes place in Ribeirão Preto, Brazil, looking at four different neighborhoods with varying socioeconomic status (SES). The four communities SES are lower class, lower middle class, traditional middle class, and upper middle class. There were four cultural domains that they were researching, including lifestyle, social support, family life, and national identity. To identify parts of the domain participants were asked to free list terms or things that are important to that domain, such as “ what things are important to have to live a good life? (Balieiro, Antônio dos Santos, Ernesto dos Santos , Dressler, 2011: 526).” This provides the investigators with many terms, these were then narrowed down to 20 to 30 terms that exemplify the cultural domain. Participants were then told to take these terms and sort them into piles based on similarities. Also participants were asked to rank order these terms from most important to that domain to least important. Depressive symptoms were measured using the Brazilian Portuguese version of the Center for Epidemiologic Studies Depression Scale. Perceived stress was measures using Cohen’s Perceived Stress Scale (PSS) that was translated into Portuguese. Three covariates were used, including age, gender, and SES. All tests were done during two separate time periods.

The results show that “the effect of cultural consonance in lifestyle is reduced to statistical non-significance (p<.10) when PSS is controlled (Balieiro, Antônio dos Santos, Ernesto dos Santos , Dressler, 2011: 531).” Also it was found that “the effect of cultural consonance in family life on depressive symptoms that is mediated by the PSS is statistically significant (z=2.75, p<.01) (Balieiro, Antônio dos Santos, Ernesto dos Santos , Dressler, 2011: 532).” It has been found that the being cultural consonant in a domain and being unable to obtain this results in depression in individuals. From these results it was concluded that the PSS somewhat resolves the depression that occurs from cultural consonance. This suggests that more research should be done, specifically looking at other cultural domains.

Balieiro, M.C., Antônio dos Santos, M., Ernesto dos Santos, J., Dressler, W.W. (2011). Does perceived stress mediate the effect of cultural consonance on depression?. Transcultural Psychiatry, 48 (5): 519-538.

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William R. Leonard is a leading anthropologist in the field of human nutrition. He was born in Jamestown, NY and received his PhD in biological anthropology from the University of Michigan at Ann Arbor in 1987. He is now an Abraham Harris Professor in the Department of Anthropology and the Chair of Anthropology at Northwestern University. He is also the Director of the Global Health Studies Program.

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Dr. William R. Leonard (left) with former student Josh Snodgrass, Univeristy of Oregon, conducting fieldwork in Siberia. (Photo provided by William Leonard)

Much of his research focuses on nutrition, energetics, and child growth in both modern and prehistoric human populations. He has traveled and studied in regions of South America, including Bolivia, Ecuador, and Peru, and also Siberia. In these regions, Leonard conducts research on population adaptation to their specific nutritional environment and how these adaptations affect their health, as well as contribute to chronic disease risks. Additionally, Leonard compiles information about human and primate ecology in order to examine the evolution of nutritional requirements in our hominid ancestors. This research leads to insight regarding the origins of obesity and metabolic diseases in contemporary human populations.

One recently published paper by Leonard, titled “The global diversity of eating patterns: Human nutritional health in comparative perspective” highlights Leonard’s work surrounding human nutrition, dietary trends, and the raising rates of obesity in the US. In the paper, he focuses on the different types of subsistence in the US versus less modern, more traditional societies. He notes that the energy intake between industrialized and non-industrialized societies is not different, but that the composition of nutrition includes higher levels of fats and carbohydrates in industrialized cultures. He also compares humans’ nutritional needs to primates, noting that the increase in brain size in higher-level primates such as humans has led to humans requiring higher quality foods than some of our close evolutionary relatives. As rates of obesity and chronic metabolic diseases continue to rise in the US and other industrialized societies, research such as Leonard’s studying the causes and origins of such nutritional deficiencies is of growing importance.

References:

Leonard, William R.

2014 The global diversity of eating patterns: Human nutritional health in comparative perspective. Physiology & Behavior 134:5-14.

Background information based on biosketch provided by Dr. William R. Leonard.

In this week’s reading, climate change and adaption among humans was the issue at hand. We learned that human-occupied environments of today are extremely different from those of tropical forests beginnings as well, historical Neanderthals. Within environments, one’s body will either adapt to hot or cold conditions. The way in which the body adapts to these environments is known as thermoregulation in correspondence with homeostasis. They body reacts based solely on its environment. With this aspect, we can also expand this knowledge into broader realms of nutrition. In direct relation with body temperature, the contraction of muscles, and acclimatization, what is put into the body helps regulate certain temperatures. Ecologically speaking, agricultural production is also based on particular environmental conditions. Without the production of fruits, vegetables, and domesticated farm animals, the average human body cannot exist very long in strenuous environments of excess heat or extreme cold. This brings to my article entitled, “Public Health and Climate Change Adaptation at the Federal Level.”

In this piece, Jeremy J. Hess and Paul J. Schramm, identify on a federal level, agencies response to an executive order by President Obama among public health and climate change adaptation. They began by exploring what climate change is, and how it contributes to executive orders of public health. “Climate change is projected to cause many adverse health effects in the United States and abroad. The adverse health effects will result from a range of direct and indirect exposures that come from shifting ecosystems dynamics; worsening air quality, increasingly frequent and severe extreme heat events; shifts in precipitation, including more frequent and severe storms and floods; sea level rise; and ocean acidification.” The Department of Health and Human resources, which houses the CDC and other agencies, take part in a wide range of activities affected by climate change. It ranges from ensuring food safety to research formulating healthcare policy. Climate change and adaptation has become such a grave issue among the CDC that federal law has to be more incorporated for health disparities as well as a larger outlook on global warming. They begin with an assessment of recent and projected future climatic shift, considers how these shifts affect agency missions and operations, and then moves toward development of adaptation plan and a formalized institutional learning component.  CDC programs range from disaster preparedness to vector-borne and zoonotic disease programs to other programs addressing global health.

Each program seeks to identify populations most vulnerable to certain impacts, anticipate future trends, and assure systems are in place to detect and respond to emerging health threats, and take steps to assure that these health risks can be managed now and in the future. In my opinion, it seems like the government is actually taking human adaption to climate change into account globally. The interesting idea about this program projection and federal law efforts is the issue around disease. I’m fully aware that climate changes and other environmental factors contribute to disease, but with ongoing epidemic of Ebola, do you guys believe this executive order is reared more toward climate adaption, or public health, or both? This article was slightly misleading in my opinion, because of the executive order, the mention of disease, but not much information on direct contact with the human bodies throughout the U.S. and abroad. In other words, all these programs may sound intriguing, but when will they be implemented and to what extent?

J. Hess and J. Schramm. Public Health and Climate Change Adaptation at the Federal Level. American Journal of Public Health. march 2014, Vol 104, No. 3.

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will-leonard3

The Author of this chapter, William R. Leonard, is currently a professor of anthropology at Northwestern University. He holds the title at this university as the Abraham Harris Professor of Anthropology. He He received his PhD from the University of Michigan in 1987. His research interests include biological anthropology, adaptability, growth and development, and nutrition focusing on populations in South America, Asia, and the United States. His most recent publication was on the topic of precursors to over-nutrition and the effects of household market food expenditures on body composition among the Tsimane in Bolivia.

The ecological variation of available food has been an important factor throughout the history of human evolution and continues to shape the biology of traditional human populations today. The relationship that humans share with their environments (i.e., acquisition and expenditure of energy) has adaptive consequences for both survival and reproduction. Humans are similar to other primates in that we are omnivorous (i.e., we eat both plants and animals) and we have nutritional requirements (e.g., the inability to synthesize vitamin C) that has caused us to adapt diets that include large quantities of fruit and vegetable material. However, what is unique to humans is our highly diverse diet (i.e., dietary plasticity) that evolved because of cultural and technological innovations that developed for processing various resources. This has allowed humans to expand into the many different ecosystems that we inhabit today.

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In order tomaintain our health, humans require six classes of nutrients:

(1)   Carbohydrates are the largest source of dietary energy for most human groups. For example, carbs account for about 40-50% of the daily calories of U.S. adults. There are three type of carbohydrates including monosaccharides (i.e., simple sugars), disaccharides (i.e., sugars formed by two monosaccharides), and polysaccharides (i.e., complex sugars made up of three or more monosaccharides).

(2)   Fats are the most calorically dense source of dietary energy and provide the largest store of potential energy for the body to do biological work. Fats are divided into three groups. The first, simple fats, is mostly made up of triglycerides (i.e., glycerol and fatty acid). Fatty acids can be further divided into saturated (i.e., found in animal products) and unsaturated fats (i.e., monounsaturated and polyunsaturated mostly found in vegetable oil). Compound fats are the second type of fat that consist of a simple fat in combination with another type of chemical compound, such as a sugar or a protein. Compound fats are important for blood clotting and insulating nerve fibers. The third category of fats is known as derived fats, which are a combination of simple and compound fats (e.g., cholesterol). Cholesterol is important for normal development and function. It is also a precursor in the synthesis of vitamin D and hormones like estradiol, progesterone, and testosterone.

(3)   Proteins are an important energy source, but they are also crucial for the growth and replacement of living tissues. In order to get theadequate nutrition per day a person needs a sufficient quantity and quality of protein. The digestibility and amino acid composition determine the quality of a protein. Complete proteins have the necessary amino acids in the quantity and proportions that are needed to maintain healthy tissue repair and growth. Good sources of complete proteins come from animal foods including eggs, milk, meat, fish, and poultry. Incomplete proteins are those that lack one or more essential amino acids. Incomplete proteins are found inplant foods, such as grains, legumes, seeds, and nuts. So if you want to be a vegetarian it will require combining different sources of plant foods in order to get all of the essential amino acids you need.

(4)   Vitamins are not a source of energy, because they just help the body use energy and carry out other metabolic activities. There are two categories of vitamins: water-soluble vitamins (i.e., B vitamins and vitamins C are needed on a daily basis because they are not stored in the body) and fat-soluble vitamins (i.e., vitamins A, D, E, and K are stored in the body so they don’t have to be taken every day). Be careful because if you take too many fat-soluble vitamins over a long period of time it can be toxic.

(5)   Minerals, such as iron, are inorganic elements that are needed in many biological molecules (e.g., hemoglobin) and are vital formaintaining various physiological functions.  

(6)   Water makes up a large portion of our body weight at 40-60% for adults. Humans get water from liquid intake, food, and “metabolic water” that is produced as the result of energy-yielding reactions.

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Recent research has focused on developing and refining energy and nutrient requirements for the various human populations around the world. Many factors must be considered in order to efficiently estimate a person’s daily energy needs including diet, daily activities and exercise, energy costs for reproduction, sex and age. According to the World Health Organization (WHO), women who are pregnant need an extra 85 kcal/day during the first trimester, an extra 285 kcal/day during the second trimester, and an extra 475 kcal/day during the final trimester. Children’s and adolescents’ energy requirements are measured differently from adults, because they have extra energy costs that are associated with growth. Pregnant women, children and adolescents also require more protein than the average adult.

The dietary patterns and metabolism of humans has been shaped by the energy demands of our relatively large brain. The energy demands of humans are usually divided into maintenance energy (i.e., needed for day-to-day survival) and productive energy (i.e., needed for growth and reproduction). Humans spend a larger portion of their daily energy budget on brain metabolism when compared to other organs in the body. We use 20-25% of our BMR (basal metabolic rate) on brain metabolism compared to the 8-10% used by primates and only 3-5% used by other mammals. It has been hypothesized that because of the high metabolic costs of our brains we require high-quality diets. Animal foods contribute to about 45-65% of the diet amonghunter-gatherers, which is much higher quality than expected for primates of our body size. Humans also have small gut volumes for our size, because most large-bodiedprimates have large intestines for digesting fibrous, low-quality diets. So, we probably evolved to have smaller intestines and a reduced colon because of our high-quality diets.  

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Throughout the evolution of the different hominin species there has been changes in brain and body size. The australopithecines had smaller brains relative to their body size, but with the emergence of the genus Homo there was a dramatic increase in brain size. The body size of Homo erectusalso increased, but the changes of the brain size were much larger than those that occurred with body mass. Homo erectus had a larger brain and body but smaller teeth, which suggests that this species relied on a different subsistence source than the australopithecines that was probably easier to digest (i.e., less fibrous plant foods) and richer in calories. The greater nutritional stability of the genus Homo provided the fuel for the energy demands of their larger brains.   

While Humans do have a diverse range of diets across the world, environmental pressures have contributed to adaptations such as lactose tolerance and the ability to digest starch. Some adaptations have become maladaptive in modern society, such as increased fat storage, which has lead to increasing rates of obesity. The amount of animal foods (meat, eggs, milk, etc.) varies across cultures and geographic location. Contemporary foraging groups consume animal foods for approximately 45-65% of their diets. However in the US our animal foods consumption is approximately 26% of our diet. Macronutrient consumption also varies across populations. Americans derive 15% from protein, 34% from fat, and a very high 51% of their energy from carbohydrates. This carbohydrate % is higher than every other population except for small-scale farmers. Another interesting statistic is the estimated consumption percentages estimated for modern foragers: 20-31% protein, 38-49% fat, and 31% carbohydrates. What do you think about these forager percentage estimates in comparison to American percentages?  

images

Carbohydrates consumed in subsistence-level societies are typically more complex with a small percentage of their carb consumption coming from simple carbs. American carbohydrates however come mostly from simple carbs and processed grains. These simple and processed carbs are absorbed faster into the blood stream than more complex varieties. A high glycemic level in the blood stream may lead to insulin resistance, which may lead to obesity, type II diabetes, hypertension, hyperlipidemia, and coronary heart disease. In comparison to subsistence-level populations, industrialized men weigh approximately 26.5 lbs more and require 150-200 kcal less. Industrialized women weigh 17.7 lbs more and demand approximately 90kcals. The US Department of Health and Human Services has also released guidelines that adults do approximately 150min/week of moderate physical activity. Another recommendation by IOM set the bar higher at 1 hour/day.

Another interesting fact from later on in the chapter is associated with the enzyme amylase. Carbohydrate digestionbeings in the mouth with amylase (enzyme found in saliva). Populations with high-carb diets have more copies of the AMY1 gene and therefore more amylase. So differences in dietin recent human evolution have exerted strong selection at the AMY1 locus. Also humans have three times as many AMY1 genes as chimps and bonobos. This implies that there was strong evolutionary selection on this gene during the early divergence of hominins from apes.

Food processing techniques are developed to fit the needs of the subsistence-level society that grows that particular crop. Corn, a major crop in the Americas, is high in protein but low in the amino acids lysine and tryptophan as well as the B vitamin niacin. To solve this problem, corn is processed in the presence of alkaliproducts (e.g., ash, lime, and lye) adding back these key nutrients. Andean populations processed potatoes in a way that removes the hazardous glycoalkaloids. Also, Asian populations processed the antitrypsin factor out of soybeans.

Climate may also have an effect on metabolic rates. Studies show that populations living in warmer climates have a lower metabolic rate than those living in colder environments. This attributes to a variation in dietary needs in different climates. It is being questioned whether these population differences are genetic or part of acclimatization.

lactose-intolerance

The ability to digest lactase disappears after weaning for most mammals, however some human populations have developed the ability to digest lactose and are thus lactose-tolerant. This change is a relatively recent evolutionary event occurring within the last 10,000 years. Genetic analysis shows that selection for the lactase persistence appeared about 7500 years ago. The allele spread across Europe in association with dairy/farming subsistence. It also appears to have evolved independently in some African populations approximately 6000-7000 years ago. However, some malabsorbers (genetically intolerant) people are able to digest lactose, and some genetically tolerant people are unable to digest milk. This suggests that dietary habits during development may contribute to lactose tolerance. In the malabsorbers this is due to an increased tolerance in the colon instead of an increase in lactase (enzyme that digests lactose. Life tip:If it ends in –ase it is an enzyme).

African-Americans have an increased risk of cardiovascular diseases. One model says that the problem is a consequence of genetic adaptation for efficient sodium (Na+) storage. Na+ is readily lost in sweat and was rare in many tropical societies. These groups have lower sweat rates and lower sodium concentrations in their sweat than European control groups. Now with salt being readily available to people who have genetically evolved to retain it, these people have higher bloodpressure. In relation to this model, the same scientist says that slaves brought over on slave ships would have been exposed to severe dehydration, and those with salt-retention would have been more likely to survive. So dependents of slaves have a high probability of having this recently selected for trait. (This study focuses on the West Indies and thereforemay not be representative of the US). Some argue that the slavery hypothesis is overly simplistic and a modern representation of racism in science. Still others argue that this increased risk is related to socioeconomic stress. Increased stress leads to increasedsympathic nervous system activity. The release of norepinephrine and adrenocorticotropic hormone elevate blood pressure by increasing sodium retention.  Do you think the slavery hypothesis is racist? Which of these models makes more sense to you?

sugar-consumption-graph

Type 2 diabetes is when your cells reduce the number of insulin receptors and then become insensitive to insulin (your insulin levels are not necessarily affected). “Thrifty Genotype” is the current hypothesis for why we evolved to be sensitive to insulin. Hunter gather societies were faced with seasonal and year-to-year fluctuations in availability of nutrients and therefore would have developed a “thrifty genotype” that would have allowed for a quick release of insulin and an increase in glucose storage during times of plenty. Nowadays we live in a constant state of plenty, and this “thrifty genotype” is now maladaptive and a contributor to diabetes and obesity. Native Americans have a very high rate of diabetes which could beassociated with the fact that they were part of a population with many “thrifty genotype” traits due to their old lifestyle, and due to the recent change in diet they are especially at risk. In addition to the ancestry view of “thrifty genotype”, recent studies also show that babies with poor nutritional conditions in early life select for “thrifty phenotype” which can also lead to increased rates of diabetes and obesity in adulthood. Could thrifty phenotype be epigenetic and passed on to offspring?

obesity_trends_20092

The obesity epidemic is a combination of all the above traits, and is associated with the transition from subsistence-level nutrition to modern-day industrial nutrition styles (processed foods, growth hormones, etc.). Thrifty genotype and phenotype are playing a huge role in populationsthat are just now gaining access to stable food supplies. Urbanization and rising incomes throughout the developing world have increased rates of overweight and obesity. Trends in US food use patterns the global trends. Energy consumed from soft drinks has increased 70% since the mid-1970’s. Available energy from vegetable oils has increased by 30% over that same time period. Other factors include the increase in eating away from home and snacking. Sugars, processed grains, and added fats are some of the cheapest food options, and with today’s bad economy poorer people are consuming more of these bad nutrients. Our modern environment has been characterized as “obseogenic”—that is, providing abundant food energy, while requiring little work or activity to produce that energy. What do you think about the obesity epidemic? Is genetics an excuse?

obesity-and-fastfood-nations

 

 

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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

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Epigenetic Mechanisms, Quick &  Dirty

Jablonka & Raz (2009) show us this elegant illustration of broad and narrow epigenetic transmission.

Epigenetic inheritance in the broad sense is the inheritance of developmental variations that do not stem from differences in the sequence of DNA...information transference that can take place through developmental interactions between mother and offspring..., through social learning..., and through symbolic communication.

We...define cellular epigenetic inheritance as the transmission from mother cell to daughter cell of variations that are not the result of differences in DNA base sequence and/or the present environment.  Transmission can be through chromatin marks, through RNAs, through self-reconstructing three-dimensional structures, and through self-sustaining metabolic loops.

In the single-cell "bottleneck" variety of epigenetic inheritance (pathway a in the above diagram) Jablonka &  Raz focus on...

The environment may induce epigenetic variation by directly affecting the germline or by affecting germ cells through the mediation of the soma, but, in either case, subsequent transmission is through the germline.

Evolutionary Implications

According to Jablonka & Raz (2009), there are 5 effects of epigenetic mechanisms & inheritance vis-a-vis evolution:

(i) evolutionary change occurring through selection of epigenetic variants, without involvement of genetic variation; (ii) evolutionary change in which an initial epigenetic modification guides the selection of correlated genetic variations; (iii) evolutionary change stemming from the direct effects of epigenetic variations and epigenetic control mechanisms on the generation of local and systemic epigenomic variations; (iv) evolutionary change resulting from the constraints and affordances that epigenetic inheritance imposes on development; and (v) evolutionary change that leads to new modes of epigenetic inheritance.

Siberian Silver Fox Experiments

The Siberian silver fox experiments are so cool, & often cite them as an example of gene linkage.  Honestly, I was just BSing in suggesting that the curly tails, rounded nose, etc. were possibly linked on the same chromosome to tameness & recognized that there might be other factors involved.  Lo & behold, a citation in Jablonka & Raz (2009) pointed us toward epigenetic studies to come out of that body of research.

Cute & cuddly silver foxes
Cute & cuddly silver foxes

It turns out that the coat spotting & non-spotting variation that we associate with domestication occurs too quickly to be pure mutation, though it behaves like a dominant & semi-dominant trait, & couldn't be explained by inbreeding because the inbreeding coefficient was too low (0.03).  Instead, they believe

the stress of domestication and selection for tameness targeted genes with large effects in the neuro-hormonal system...and may have heritably reactivated some of them...This epigenetic interpretation, in terms of new epimutations rather than new mutations, explains the high rate of appearance and disappearance of some phenotypes, and support for this comes from the fact that at least two of the genes (Agouti and C-kit) that seem to be involved in the changes are known to have heritable epigenetic variants in mice...

One aspect of epigenetics that seems important here is the concept of canalization, introduced by Waddington several decades back (he also introduced the concept of epigenetics in general, which everyone rightly thought was Lamarkian & wrongly ignored--turns out he was on the money).  Roughly, canalization means that some environmental perturbation pushes a phenotype into a canal or valley, whereafter selection pressures prevent the phenotype from returning to its previous state because the "climb" up the sides of the canal or out of the valley are too steep.  Think of a marble on a tabletop that is essentially flat but has a valley to one side of it.  Stochastic chance dictates that the marble can roll any which way, but if it happens to roll toward the valley, it gets stuck there & can only roll further in the valley.  Or as this image illustrates, there are several possible environmental variations possible, but once a phenotype goes one way (plastically), it cannot go back.

So it seems to be with the silver foxes.  Once an environmental condition pushes silver foxes (or wolves before them) one way (luring tame ones to their yummy debris & handouts) or another (spooking the nervous ones to run away), a cascade of epigenetic mechanisms pushes them further along.  At that point, according to this model, tame ones cannot become anxious/aggressive & vice versa.

While cute silver foxes that you can cuddle with get all the press, the less publicized but equally fascinating is the aggressive foxes that want to rip your face off.

Aggressive domesticated silver fox Courtesy of Lyudmila Trut / Institute of Cytology andGenetics / The Siberian Division of the Russian Academy of Sciences (Source: Dugatkin 2003, http://www.dana.org/news/cerebrum/detail.aspx?id=2922)
Aggressive domesticated silver fox Courtesy of Lyudmila Trut / Institute of Cytology andGenetics / The Siberian Division of the Russian Academy of Sciences (Source: Dugatkin 2003, http://www.dana.org/news/cerebrum/detail.aspx?id=2922)

So what's going on with these aggressive foxes?  According to Popova (2006), there are at least 16 genes that influence aggression, but most aggression behavior is influenced by just a few of those.  A major player seems to be serotonin (5-HT).  The 5-HT pathway in the brain suppresses aggression.  5-HT is not a gene though, it is a hormone; & genes code for proteins.  So if there's a gene change, what is/are the gene(s)?  It could be any gene that produces an enzyme involved in the essential mechanisms of the 5-HT system, which include synthesis/degradation, reuptake in the synaptic cleft, & density/sensitivity of receptors (for more background on 5-HT, I've written on this before here).  As the figure below illustrates, there are enzymes that catalyze serotonin synthesis (TPH & decarboxylase of aromatic l-amino acids), two enzymes that help break serotonin down (MAO A & B), & an enzyme (SERT) that transports serotonin.

There are two TPH genes, & it is the 2nd one (TPH2), expressed in the brain & responsible for the central nervous system, that effects 5-HT & seems to be responsible for aggressive behavior.

Silver foxes displaying friendly responses to human contact were shown to have higher 5-HT and 5-HIAA levels, and higher TPH activity in the midbrain and hypothalamus in comparison to nonselected wild-type silver foxes bred in captivity. Importantly, the changes were found in the midbrain representing the area of main location of TPH2-synthesizing cell bodies.  These findings were interpreted as an indication of an increased activity of the brain 5-HT system in the tame animals and, subsequently, a decreased activity of this system in highly aggressive animals.

MAO A has a higher affinity for 5-HT & is considered the principle enzyme in breaking down serotonin.  When MAO A is disrupted in mice, they get more aggressive.  Deletion of SERT (the transporter that allows 5-HT molecules not taken up by post-synaptic receptors to be recycled & reused) in knockout mice also produces aggressive behavior.  Finally, there are 14 different subtypes of 5-HT post-synaptic receptors.  Genetically low aggression has been associated with increased expression of specific subtypes of these receptors in the midbrain & specific densities & function in specific regions of the brain.  These likely function to suppress aggressive behavior.

The figure below depicts this as essentially two pathways, which we can compare analogously to the Jablonka & Raz depiction of the narrow "bottleneck" pathway, albeit via two cells (or genes).  I think.

If any one of these mechanisms or either of these pathways influences aggression, they will interact with the environment to mutually reinforce themselves & push the marble down toward the other pathway too.  In other words, if the stress of domestication bumped the marble off the plane, having even only a slightly higher tendency of aggression relative to tameness will result in amplification of the entire aggression pathway, even if the environmental conditions of captivity are thereafter removed (i.e., the animal is released).  What still remains to be clarified is how the initial brain changes occur & the roles of other mechanisms in the system.

Zane Thayer & Chris Kuzawa review data that offer a clue.  They point out that "psychosocial stress contributes to the social gradient in health" (2011:799).  This is well-established by now, but the mechanisms are interesting.  In two studies particularly relevant to our question of how the stress of domestication may influence aggression in silver foxes, childhood abuse was associated w/ methylation differences at the GR (glucocorticoid) locus in the hippocampus & the serotonin transporter protein (SLC6A4) locus.  Another study found that maternal depression during pregnancy predicted stress reactivity & methylation of the GR locus in buccal cells of their infants 3 months after birth.  Methylation is the addition of a methyl group to a substrate or substitution of an atom by a methyl group.  This can take place in DNA or proteins.  In DNA, it can result in the change of an amino acid base, thus a change in the genetic code resulting in production of different or altered proteins.  In proteins, it results in regulatory changes in the protein functions, so methylation can have wide-ranging effects.  The methylation of the GR receptor locus may affect things like the binding of glucocorticoids to the receptor.  Glucocorticoids are best known for their role in stress response, but, relevant to this discussion, they are also operative in memory consolidation and learning, as contextual fear conditioning, among many other functions.  The SLC6A4 serotonin transporter protein terminates action of serotonin in the synapse & recycles it, which is a key function in mood stabilization.  Low serotonin is associated with high fear response.

So the psychosocial stress of domestication in some silver foxes could result in methylation of glucocorticoid & serotonin receptors, directly influences fear/aggression response in pups, that persists throughout their lives.  It can also influence depression in mothers that is passed on in the receptor activity of their pups.  We can link this with Larry Schell's model of risk-focusing.  Replace "SES" with "personality."  Fear/aggression in mothers increases the risk for fear/aggression in descendants, as tameness in mothers increases the risk of tameness in descendants.

Larry Schell's risk-focusing modelAlthough the model above suggests gene line changes, the broad epigenetic view suggests that some of these influences may not influence the germ yet still persist over multiple generations because of the influence that maternal disposition has on offspring gene expression.  Or, as Thayer & Kuzawa note

...Genes are regulated by biological "memories" of experiences acquired earlier in our own lives, and even by recent predecessors... (2011:801)

17

Biographies

Michael A. Little

Dr. Michael A. Little possesses the title of “distinguished professor” at Pennsylvania State University (where he also earned both his masters and PhD). He began his research career examining cold adaptation in the high Peruvian Andes before he began a 20 year, multidisciplinary project that studied the health, biology, and culture of pastoralists in northwest Kenya. His current work focuses mainly on documenting the history of biological anthropology mainly, through archival research. He teaches classes at PSU on comparative human growth, human biological variation, and the history of biological anthropology. In 2005, he received the Franz Boas award from the Human Biology Association and later, in 2007, received the Charles R. Darwin award from the American Association of Physical Anthropologists.

Francis E. Johnston

Dr. Francis E. Johnston is Professor Emeritus of Anthropology at the University of Pennsylvania, where he also earned his PhD (his masters was earned at the University of Kentucky). He specializes in the study of the development of children in Latin America, particularly in regard to nutritional status and health. He is the founder and director of the Urban Nutrition Initiative. He was President of the American Association of Physical Anthropologists from 1983 to 1985 and has been the Editor-in-Chief of The American Journal of Physical Anthropology, Human Biology, and The American Journal of Human Biology (where he was also founding editor). In 2003, he received the Charles Darwin Lifetime Achievement Award of the American Association of Physical Anthropologists.

Human Biology and Its History

  • Timeline
    • Middle Ages: the earliest form of human biology begins with the study of cadavers to determine bodily structure
    • 1924: Raymond Pearl is the first modern scholar to use the term human biology
      • Discussion: Since this chapter focuses only on the history of American human biology (due to space restrictions), what kind of biases do you think could be present, if any?

Human Variation

  • Timeline
    • 1850-1940s: the measurement and description of past and present humans in the form of a typology is popular
      • Typologies can be problematic since they represent more of an idealized image than reality.
      • Eugenics arguing for the superiority of Western Europeans were popular at the time
      • It was believed that all races were: 1) fixed, 2) came from three primary races, and 3) were one of the primary races or a mixture of two or three primary races
      • 1897: Franz Boaz measured the heads of migrants and their children, showing that the environment and plasticity were important factors in variation
        • He stated that race and culture were separate
      • 1950: The new phase of physical anthropology begins with a conference held by Theodosius Dobzhansky and Sherwood Washburn
        • The use of the scientific method in the study of evolutionary theory became the new focus of this phase of anthropology
      • 1950: Races: A study of the Problem of Race Formation in Man, written by Carleton Coon, Stanley Garn, and Joseph Birdsell, argues that racial categories formed to the conditions of the environment via natural selection
        • Race was seen as ever-changing instead of static
      • Currently: race is no longer a subject of study, with the exception of clarifying misusages of the term that lead to discrimination. Human variation is viewed as dynamic.
        • Discussion: What are some current examples of the misuse of the concept of race? How are these examples different from misusages in the past?

Human Adaptability

  • 1950s: Bodily adaptation to the environment is viewed as happening largely in terms of adaptation to climate (particularly temperature extremes)
  • 1960s—1970s: The International Council of Scientific Unions (ICSU) implemented the International Biological Programme (IBP)
    • Human adaptability studies were a part of this, though the more scientifically inclined methodology of the research kept some human biologists from participating
    • Ecosystems science (a combination of ecology and the mathematical study of systems science) became popular
    • The physiological measurements that were also taken at this time allowed for the study of how populations adapt biobehaviorally to the environment
    • Many of the projects conducted by the human adaptability section of the IBP were multidisciplinary projects
      • Discussion: What are the advantages and disadvantages of a large-scale study such as the human adaptability research at the IBP?

Anthropological Genetics

  • Timeline
    • 1860’s- Mendel experiments with peas to develop the laws of  segregation and independent assortment
      • Explores dominance in alleles
      • Compares genotype to phenotype
    • 1927-1930- JBS Haldane and Robert Fisher expressed evolution as the aggregate effect of interactions between mutations, gene flow, selection, and genetic drift
      • Integrated Darwinian theory, population genetics, and advanced mathematical analyses
      • Let to the rise of the two modern approaches to the interpretation of patterns of gene frequency
        • One focuses on natural selection
        • One focuses on the stochastic processes of genetic drift and gene flow
    • 1900- Karl Landsteiner provides first description of human ABO blood type groups
      • Discovery of these and other antigens revolutionized immunology and segued into the study of human population genetics
      • Later found that the frequencies of these antigens are shaped, at least in a small degree, by natural selection
    • 1950- William Boyd argues against the use of anthropometry
      • Wanted scientists to focus on genetics that were not shaped by environment
      • Still believed in race as a true biological category
    • 1958- Frank B. Livingstone analyzes the distribution and dynamics  of the hemoglobin S (sickle-cell) gene
    • 1987- National Institutes of Health begin the Human Genome Project
  • Review and Discussion
    • Darwin’s description of natural selection was not complete until Mendel completed his work with the pea plants
      • Where do you stand on the issue of the main force behind evolution? Do you agree with E.B. Ford who argues that genetic polymorphism is maintained by selection and that gene frequencies are kept in equilibrium by opposing selective forces? Would  you say that population demographics like age structure, mortality rates, sex ratio, and migration/immigration patterns have the strongest  impact on the genetic variability within a population?
    • The Modern Trends
      • Most of the study of human genetics has  been at the level of DNA
      • The Human Genome Project focuses mainly on alleles considered responsible for disease
        • What else could be studied through the mapping of the human genome?
        • What portion of disease patterns do you consider to be affected by genetics and what portion of the pattern is affected by culture/environment?

Growth and Development

  • Timeline
    • 1948- Wilton M. Krogman starts to study the “whole child” and is       considered the “father” of growth studies in America
    • 1970- Though incorrect, Rose Frisch developed a hypothesis about the relationship between a “critical weight” and menarche in young females, thus sparking the interest in reproductive ecology popular in the 1980’s
    • 1986- Elizabeth Watts introduces an evolutionary perspective to the study of human growth
  • Review and Discussion
    • Franz Boas is considered the first to emphasize longitudinal studies when examining growth and development?
      • Why had few people done these before? What are the benefits? Do the benefits outweigh the numerous complications?
    • The new interest in human growth also opened new avenues on exploring the interactions between biology and the environment
      • Human ecology emerges, initiating studies that examine the physical changes that occur in people who live in extreme conditions
      • The exploration into the sub-division of reproductive ecology led to the discovery of the many environmental (and cultural) variables that influence reproduction and infant care
      • What framework were anthropologists previously using to examine         reproduction? 
    • The thrifty phenotype
      • First appears in the early 90’s
      • Based on the concept of developmental plasticity
      • States that some adult diseases can be associated with earlier growth patterns
      • How do you feel about the accuracy of this hypothesis? How could it be tested?

Biomedical Anthropology

  • Timeline
    • ~1960- Albert Damon describes the health significance in variations in physique
  • Review and Discussion
    • Four related factors that culminate in the discipline known as “biomedical anthropology"
        • The plasticity of human variability
        • Concept of “risk factors” refined by the field of epidemiology
        • Primary affiliation of many “human biologist” with the medical or dental industries
          • How would having a medical background assist a physical anthropologist? Could it be a hindrance? Or does it not really make a significant difference? 
        • The emergence of Darwinian (evolutionary) medicine
          • Examines the evolutionary aspects of contemporary human diseases
          • Includes “diseases of civilization,” representative of the fact that early adaptations to preindustrial life have become maladaptive in a contemporary, urban society
            • The book lists obesity, cardiovascular disease, and sudden infant death syndrome as examples, can you think of any others?
        • The realization of functional lifestyle changes that occur in immigrant populations
          • Focuses particularly on stress arising from culture shock and a change in social structure
          • Can culture also “cure” some of these stresses by providing a new form of adaptation?