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Friedrich Leopold August Weismann

640px-August_Weismann

Educational Background/Training

Weismann was born on 17 January 1834 in Frankfurt am Main, in the German Confederation. His mother, Elise Eleanor Lübbren, was a musician and painter, and his father, Johann Konrad August Weismann, was a classics professor. Weismann studied music, particularly the works of Beethoven, and he studied nature, from which he collected butterflies. He noted diverse patterns and colors of butterflies, information that later informed his research on the development and evolution of butterflies and caterpillars.

In 1856 Weismann got his medical degree from the University of Göttingen in Göttingen, in the German Confederation. After graduation, Weismann worked as an assistant in a hospital for three years in Rostock, in the German Confederation, before becoming a physician in Frankfurt am Main in 1859. From 1861 to 1863, Weismann was the private physician for Archduke Stephen of Austria. In 1861, Weismann studied at the University of Giessen in Giessen in the German Confederation, with Rudolf Leuckart for two months, working on the ontogeny (development) and morphology (form) of animals, insects in particular. That year, Weismann read Charles Darwin’s On the Origin of Species two years after it was published in 1859, after which he adopted evolutionary theory. Weismann studied different factors he thought might cause morphological transformations in insects, including natural selection.

In 1863, Weismann became a docent in zoology and comparative anatomy, a mid-ranking academic position, in the University of Freiburg in Freiburg in Breisgau, also in the German Confederation. In 1864, Weismann’s eyesight declined, which left him partially blind and limited his ability to use microscopes. Nonetheless, he studied the metamorphosis and development of butterflies. Weismann became the founding director of the Zoological Institute at the University of Freiburg in 1867. That year, he married Marie Dorothea Gruber from Genoa, Italy. The couple had at least five children. Along with his students and assistants, Marie aided his experimental and observational studies after his eyesight failed. Marie died in 1886, but Weismann remarried at the age of sixty in the mid-1890s to Willemina Tesse from the Netherlands, a marriage that lasted six years.

Summary of Research

            August Friedrich Leopold Weismann studied how the traits of organisms developed and evolved in a variety of organisms, mostly insects and aquatic animals, in Germany in the late nineteenth and early twentieth centuries. Weismann proposed the theory of the continuity of germ-plasma, a theory of heredity. Weismann postulated that germ-plasma was the hereditary material in cells, and parents transmitted to their offspring only the germ-plasma present in germ-cells (sperm and egg cells) rather than somatic or body cells. Weismann also promoted Charles Darwin's 1859 theory of the evolution of species. Weismann argued that only changes to the germ cells, and not body cells, could be inherited, a theory that influenced theories of heredity throughout later centuries.

From 1881 onwards, Weismann published a series of essays about heredity. Those essays were collated in English in 1889's Essays upon Heredity and Kindred Biological Problems. The essays discussed topics including senescence, acquired characteristics, and the germ-plasma theory. For example, in the first chapter, "The Duration of Life," a translation of an essay originally published in German in 1881, Weismann detailed his evolutionary theory of senescence, the name given to the gradual deterioration of function of most life forms after they mature to adults. Weismann argued against theories that associated the length of an organism's life with the size or complexity of its body, or with how active it appears to be. Instead, he appealed to natural selection, arguing that it adapted organisms to reach reproductive maturity, and that it would not select for the capacity of the organism to live any longer once it was past reproductive age. He further argued that the death of male bees after they reproduced was selected for by nature to save nutrition for the colony, a phenomenon that precluded those organisms that had already reproduced from consuming resources.

Linking his work to broader context

When Weismann’s germ theory is paired with that of Gregor Mendel’s on inheritance we are provided the basic understandings of how humans and other animals inherit their traits from their parents. Weismann used his germ theory to explain that, “natural selection favors organisms that pass on their germlines before conspecific and before extrinsic factor cause their death (Crews and Ice, 2012: 639).” This statement has been used to create the concept of life history theory for many different species, including humans. For life history theory, we see that the goal to reproduce is in conflict with the maintenance of the body. This result in trade-offs that the body goes through in order to chose one of these actions over the other. The allocation of resources between reproducing and somatic maintenance created a way for researchers to compare and to structure their research as to why these chronic diseases and changes in old age occur. Through these trade offs in life history theory is how Weismann can be connected to this chapter. This chapter discusses the aging and senescence of humans. Senescence occurs when the body begins to function less efficiently and cell begins to functioning deteriorate as life progresses. The chapter discusses the different ways that the body ages in multiple areas, including hormones, immune system, cardiovascular, body composition, bone, dementias, and reproductive aging. All of these areas are altered through the aging of an individual based on the life history course that has been taken. One problem with Weismann’s concept of life history is that it does not allow for the environment and culture to alter these stages. Even in the chapter there is little discussion on the environment and its effects on life history. Yet, with the time that Weismann came up with this theory there must be credit given for his ability to come up with these conclusions that further lead to our understanding of how the body works.

Crews, D.E., Ice, G.H. (2012). Aging, senescence, and human variation in Human Biology: An Evolutionary and Biocultural Perspectives, Second Edition. Edited by Stinson, Bogin, O’Rourke. John Wiley and Sons, Inc.: Hoboken, New Jersey.

(2008). August Weismann found at http://www.encyclopedia.com/topic/August_Weismann.aspx.

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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.

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Rebecca L. Cann is a geneticist who, along with her colleagues, is best known for the Mitochondrial Eve hypothesis (1987). Mitochondrial Eve explains that our human mitochondrial DNA can be linked back to a single African mother from over 200,000 years ago. The Mitochondrial Eve is the ancestor of us all. Since the publication of her paper in 1987, Cann's finding have had a huge impact on human society by contributing evidence for the "(Recent) Out-of-Africa" model.

Rebecca Cann was originally born in Burlington, Iowa. She moved to San Francisco right before starting high school. After graduation, she earned her bachelor's (1972) at the University of California, Berkeley. In the gap between earning her Bachelor's in Genetics and enrolling for graduate school in the Anthropology Department (1972-1974), Cann's interests in human variability and personalized genomes ignited while working as a night-time quality control chemist. Her job exposed her to a lot of scientific journals and articles that made her very inquisitive in how human genotypic variation creates such different phenotypes. Upon learning about restriction enzymes in 1974, Cann decided to enter graduate school to work in molecular anthropology and human evolution. She earned her doctorate in 1982 under the supervision of Dr. Allan Wilson. She worked her Postdoctoral at Howard Hughes Medical Institute until joining the faculty of Univerity of Hawaii's Department of Cell and Molecular Biology in 1986. The following year Cann's "Mitochondrial DNA and human evolution" paper was published Nature (1987).

Currently Cann is a professor at the University of Hawaii.

"Raymond Pearl." Via Wikipedia - http://en.wikipedia.org/wiki/File:Raymond_Pearl_o.jpg#mediaviewer/File:Raymond_Pearl_o.jpg
"Raymond Pearl." Via Wikipedia - http://en.wikipedia.org/wiki/File: Raymond_Pearl _o.jpg#mediaviewer/ File:Raymond_Pearl_o.jpg

Raymond Pearl, Professor of Biology in the Medical School and in the School of Hygiene and Public Health of the Johns Hopkins University, died at Hershey, Pennsylvania, November 17, 1940, at the age of sixty-one years. At the age of 16 he entered Dartmouth College, expecting to make the classics his chief field of study. During his first year he was more interested in the opportunities for free activity than in his studies; a fact which was reflected in the low grades which he received. But in that first year biology was a required subject, and this opened his eyes to what became his main interest. He graduated from Dartmouth with the degree of A.B. in 1899. According to the Class Report before cited "Pearl was the youngest graduate in our class." During his senior year he was assistant in the course in general biology, of which the present writer was at that time in charge. He showed at that early period the masterful and competent personality that marked him throughout life.

In the fall of 1899, Pearl went to the University of Michigan, while for three years he was an assistant in Zoology while at work as a graduate student. He took part in the Biological Survey of Great Lakes, founded and led by the late Jacob Reighard working on variation in fishes (1900- 1902). He received in 1902 from the University of Michigan the degree of Doctor of Philosophy, at the age of twenty-three. From 1902-1906 he was a professor of Zoology at the University of Michigan. It was in the laboratory of the University of Michigan where he met Maud. M. De Witt, who became his wife. They were married in 1903, and upon his death bed she became managing editor of the journal “Human Biology”, and assistant editor of the ‘Quarterly Review of Biology”- the two journals founded and edited by Pearl. In the year of 1905-1906, Pearl he decided to enter the field of the application of statistical method of Biological problems with Karl Pearson at the University College, London. During the same visit to Europe he worked also at Leipzig and at the Marine Biological Station at Naples. Pearl returned to America in 1906, and was an instructor in Zoology at the University of Pennsylvania in 1906-1907. In 1907, he went to the University of Maine in Orono, as head of the department of Biology of the Maine Agriculture Experiment Station, remaining there until 1918. In 1918, Pearl was called at instance of Dr. William Welch, to become professor of Biometry and Vital Statistics in the newly found School of Hygiene and Public Health of John Hopkins University, where he spent the remainder of his educational career and training.

Before Pearl received his doctorate, he published a number of contributions. His dissertation was on the actions and behavior of Planarians. He next contributed a series of papers on genetic problems in lower organisms in which he worked with Karl Pearson in London. Also while in London, he finished and elaborated statistically a valuable piece of work on assortative mating in Protozoa. While at John Hopkins University, his interest in many subjects was so intense that at any given moment he might seem a partisan and propagandist of a particular method of biological science. Among the seven hundred and twelve titles (including seventeen books) in the list of Pearl’s writing hereto appended will be found contributions on the most varied fields of aspects biology or as human affairs as a division of biology. There are papers on animal behaviors, to Protozoa to man; on general physiology; many of various aspects of genetics (on abnormalities, variations on the breeding of Drosophila, of poultry, of cattle, of corn, of cantaloupes, on tongue colors in cattle, on the color hen’s eyes, etc.) There are many technical contributions on the care and breeding and fowls (fertility and diseases of fowls, plumage patterns, egg production, keep fowls free from lice, and folk-lore of hens’ eggs). Furthermore, many papers deal with the biology of man: papers on longevity and mortality, on the effects of alcohol and tobacco, on eugenics, and race culture, on the biology of superiority, the biology of death, infant mortality, and contraception.

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bogin_528

Barry Bogin is an American physical anthropologist trained at Temple University that researches physical growth in Guatemalan Maya children, and is a theorist upon the evolutionary origins of human childhood. He is currently at Loughborough University in the UK. He is noted for the idea that evolution added two new stages into human development; childhood and adolescence.

 

Smith,B Holly

B. Holly Smith is a Associate Research Scientist in the Department of Anthropology at the University of Michigan at Ann Arbor where she got both her Master and Ph.D. She is interested in  how humans differ from other mammals in life cycle and life span, why we differ and whether we can reconstruct the evolutionary history of our life cycle from the fossil record.

This chapter was about the evolution and alterations of the human life cycle. The main questions that guided this research were:

  • How can human biologists identify the shared and novel features of the human life cycle?
  • Can the time of origin of the novel features be determined?
  • Can the reasons for the evolution of new growth development and maturation patters be determined?

 

Stages in the Life cycle

There are four main stages in the human life cycle Birth, Postnatal Development, Adulthood, and Death. Of these, both postnatal development and adulthood are divided up into sections. Pregnancy (the period before birth) is divided into trimesters and during this gestational period, the fetus grows and changes and experiences critical periods. These are times when a fetus is particularly susceptible to outside factors such as diseases or lack of nutrients. During this time the fetus can undergo epigenetic modification.

What other outside factors can affect a fetus in vivo?

 

After the pregnancy comes birth, a rapid transition from a fairly stable liquid environment to a volatile gaseous one. And after this period come the postnatal development. This is the most complex of the stages and is divided up into these sections

  • Neonatal period
  • Infancy
  • Childhood
  • Juvenile
  • Puberty
  • Adolescence

Which of these sections is the longest and why do you think that is?

In which of these stages is proper nutrition the most critical for brain development, and why is this so?

 

Why did new life stages evolve?

If we look at the life cycles of other large primates we see that although humans experience delays in Molar 1 eruptions, menarche and 1st births, humans have less spacing between births (3 years for humans, 6 for chimpanzees). This gives humans the advantage to give birth to more offspring. So we find that our evolution of childhood gives us the reproductive advantage although it does come with some drawbacks. Children need specialized diets and extended periods of care, as they do not become self sufficient until post-adolescence.

Although we cannot study the life cycles of an extinct organism, we can postulate it by looking at currently living species. In looking at archaeological evidence, we can see that there is an increase in brain size in cubic centimeters and that because of this, there had to have been an increase in postnatal stages. When we get to homo sapiens we see the appearance of adolescence.

Which organism(s) would be useful in looking at early human life cycles?

What physiological changes needed to occur in early human ancestors to accommodate larger brains?

 

Food for thought

  • How would we be different if we had a shorter postnatal period?
  • Would anything be different if humans waited (on average) twice as long between children?

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Carol Worthman received her PhD at Harvard in 1978, after first attending Pomona College for her BA in Botany and biology, and subsequently the University of California at San Diego Medical School and Massachusetts Institute of Technology. Her interests include biological anthropology, human reproduction, human development, biocultural and life history theory, and developmental epidemiology. These interests are bioculturally focused. She also has worked with the University of Alabama's own Dr. Jason DeCaro on various projects concerning stress and developmental biology.

Brandon Kohrt is an assistant professor at Duke Global Health Institute and Department of Psychiatry and Behavioral Sciences. He conducts global mental health research focusing on populations affected by war-related trauma and chronic stressors of poverty, discrimination, and lack of access to healthcare and education. His research is conducted in Nepal, and he has worked closely with the Transcultural Psychosocial Organization (TPO) Nepal, the Carter Center Mental Health Liberia Program, and was a co-founder of the Atlanta Asylum Network for Torture Survivors. His interests include culture, health economics, health systems, and mental health.

Worthman and Kohrt are concerned with how our current approach to public health is dissonant with contemporary health concerns. They call this phenomenon a "paradox of success," which is characterized by historical accomplishments in public health perpetuating paradigms which cannot be applied globally or to recent emerging health concerns. Sometimes these paradigms result in negative effects on health, which I will explain below. According to multiple sources, only 2-60% of health outcome variation is explained by the models we currently use in public health (see Worthman & Kohrt 2005). In order to evaluate and adjust public health models, Worthman and Kohrt identify five paradoxes stimulating morbidity instead of expected success.

  1. Unmasking is characterized by changes in morbidity patterns. Advances in health care have created an epidemiologic transition from infectious disease to chronic degenerative and mental illnesses. Think cancer, Alzheimer's, etc... The example used in the article was depression, although the rise in mental illness could also be a result of historically unreliable data.
    What other examples of unmasking can you think of?

    Simplified model of epidemiological transition.


  2. Localization is an important paradox resulting from globalization of public health paradigms. It is becoming increasingly evident that biological function and regulation are heavily dependent on context. Vaccinations sometimes fail as a result of locally derived immunocompetence. Fetal/childhood development also play a role, as shown by the relationship between breastfeeding/birth spacing and infant survival/health.
    The article talked about fetal programming as a factor of localization. What about research in fetal programming is relevant here (in the article or outside)?

    Anti-vaccine propaganda. Success of vaccination can be affected by malnutrition, pathogen load, stress, and immune development of individual.


  3. Socialization in this context applies to the enhancement or diminishing of vulnerability to disease based on cultural factors. HIV/AIDS prevalence in African countries are exacerbated by cultural attitudes toward sex and the availability of sex education, as opposed to Western countries.
    What are some examples of cultural practices that perpetuate disease?

    Fast food culture... you can find these anywhere!

     

  4. Re/emerging disease is a resurgence of disease patterns, sometimes in more virulent forms. Tuberculosis is an important example, responsible for 3% of all mortality in 1999. Diabetes and asthma are other examples, although literature on  re-emergence of non-infectious disease is currently limited.
    What factors contribute to re/emergent diseases?

    Travel is just one factors contributing to re/emerging disease.
  5. Savage inequity adds fuel to the previously mentioned paradoxes. Poverty, inequality, and inequity are all included under this paradox. Global media especially perpetuates inequity and can be the cause of varying psychosocial factors that contribute to morbidity.
    What is the difference between inequality and inequity, and what are the health implications of each?

    Link between risk factors and income levels.

I thought about tuberculosis as an historical disease until I had to take my TB test before entering college. I wasn't positive, but the test indicated that I had been in contact with the disease at some point. I didn't realize that our health practices were, in a way, catalyzing the resurgence of antibiotic-resistant tuberculosis. Savage inequity is also a concept the resonates with me. Intuitively, I know that mental health is just as important as physical health, but this knowledge conflicts with what I've observed in medicine and health research. I only recently realized that this is a problem with the paradigm, not my understanding or health.

I also think it's important to note that, although socialization and local biology seem obvious contributing factors to health in our class, we are anthropology students. It appears to me that medical students are vastly under-educated regarding biocultural models of medicine. I won't pretend to know how to change education policies in medical school, but it is important to recognize that a global public health paradigm isn't going to satisfy our global health needs.

 

EDITED 12-9-2013

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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?  

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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

 

 

8

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

3

If you've been reading some of the blogs on this site, you probably know by now that the Biology, Culture, and Evolution class has the opportunity to do genetic testing this semester. I've always thought ancestry was fascinating, and my mom's side of the family has much more mystery surrounding our heritage so I would really like to find out what I can about that. However, I'm also looking forward to some of the information they can give me on genes more pertinent to my daily life and my future.

I am interested in the health issues that 23 and Me will test. I am especially interested in the genes for Tourette's Syndrome and restless leg syndrome. I have read some research recently that Tourette's, RLS, and other tic disorders are very closely related genetically. I have a chronic tic disorder, which is on a scale between Tourette's (requires motor and vocal tics to diagnose) and transient tic disorder (which is in kids and lasts less than a year). My mom has restless leg syndrome, but no one else in the extended family has a related disorder that I know of. Over the next few weeks I do plan on contacting my mother's sisters to see if they, there children, or their grandchildren have restless leg or tics. This is important to me because I'd like to know the likelihood that, if I do have children, they will have a tic. My family has history of stroke on both sides, so I'd like to look at the genetic side of that and how certain medications will affect that.

I'm really excited about having the opportunity to have my genes tested with my Biology, Culture, & Evolution class. I am looking forward to learning more about my ancestry. All I know is that at some point my ancestors lived in Ireland and Scotland, and on my mother's side my great-great grandmother was a Choctaw Indian. I think it will be really cool to find out more about my ancestry even further back than that. I also think it will be really beneficial for me to know which diseases I'm at risk for. High blood pressure and cardiovascular disease run in my family on both my maternal and paternal side. If I am at greater risk for that, I can make sure to maintain a healthy diet and exercise in order to prevent those diseases. However, I am a little worried about finding out that I may be at a greater risk for developing Alzheimer's because my granddad on my mother's side had it. If I am at a higher risk for it, there isn't anything I can do to prevent it. I'm haven't decided if it will be a good thing to know ahead of time, or if it would just cause unnecessary worrying.
I think it will also be advantageous to know which types of medication would work best for me and which ones I should avoid. I do think it would be beneficial to know what diseases I am a carrier for so that I can be aware of any problems that might occur when I do have children.