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When I did 23&me I was most excited to learn about my ancestry. My 23&me results were somewhat disappointing. Both sides of my family claim some Native American ancestors, but 23&me says that I am 98.4% European and of that 79% Northern European with the rest being non-specific European. I am only 0.8% Native American, which is enough to show that there might be something in my past, but not as recent as some family members would like to say.  I have a small amount of German/French ancestry (3.4%), but the cool part about that is that it is all located together on one of my two second chromosomes. So I have almost an entire chromosome that is from German/French ancestry. The 0.8% Native American is also together in one piece indicating that it came from one place, which is pretty cool. I could be possible that the genes from my Native American ancestor were lost during crossing over events in my parents, grandparents, great-grandparents, etc. So there still could be more Native American ancestry than what shows up. So I now know a lot more about my extended heritage, but nothing ground breaking or exciting was found.

Probably one of the coolest ancestry things I found is that I am 3% Neanderthal putting me into the 88th percentile. That is pretty cool, and makes sense with my Northern European ancestry.

When it came to my health results, there was only one thing that was major for me: I have two copies of the APOE ε4 variant. This increases my risk for Alzheimer's to 39.9%. If you have a family history, you can assume that this is correct or even raised. My grandmother and two of her siblings are currently suffering from the disease. My risk factor for this is extremely high, and this is pretty scary. I'm not really sure what all there is that I can do about this. There are no confirmed ways to prevent it. I'm not guaranteed to get the disease, but with my family history, I have to admit that it is extremely likely.

There really wasn't anything else significant that I found. It knew my hair color, and eye color. One other thing I found interesting is that I am "likely a sprinter." I've never been much for exercising, but running has always been my preferred thing to do if I am going to exercise regularly. Maybe I should start running more often.




Sara Stinson is a professor at CUNY Queens College.  She received her Ph.D. from University of Michigan in 1978.  Her focus is on physical and developmental variations among living human populations.  She studies environmental influences on growth and the evolution of body size.  Her research has been mostly on South American populations, including variation in indigenous South American populations, effects of high altitude hypoxia, and growth of lowland tropical forest populations.



Growth Variation: Biological and Cultural Factors

Variation in size is one of the most obvious ways that humans differ. These differences are also easy to measure and compare across populations, making this a well-studied topic in biology/anthropology. Many factors can contribute to growth variation across and among populations such as genetic factors, nutrition, environmental conditions, social conditions, and cultural conditions.


Genetic Factors:

Genotype can have a strong effect on growth as shown in the next two examples. Our ancestry and previous natural selection pressures on our ancestors affect growth patterns.

The range of the average height for the tallest and shortest populations is less than one foot. The shortest population, the Efe pygmies of central Africa, is less than 5 ft. tall on average.  While poor nutrition plays a role, it has been shown that these populations have a reduced number of sites for growth hormone to attach on their cells which would lower the effect the hormone has on them. Smaller body size could have been selected for since it would be advantageous to be small in this hot, humid environment, but no genes that could be attributed to natural selection have been identified.

Another genetic example of growth variation is the difference in males and females. In the US male and female average height is approximately 6 inches different.  The height ranges can be represented by two overlapping bell curves. While males tend to be taller, females tend to carry more subcutaneous fat than males, and females carry their weight in different areas than men.  These sexually dimorphic tendencies exist in every human population, and are contributed to by hormonal differences during adolescence and puberty.


Environmental Factors:

Most size variation in the world’s populations is attributed to environmental factors.

Socioeconomic Status is one of the major players that can contribute to size variation. Socioeconomic status can limit access to quality health care and nutritious food, while having an increased exposure to disease. Scientists can look at income, education, occupation, and household possessions to determine this status. In almost EVERY study done so far children from high-income families are taller than children from low-income families. This difference is more noticeable in developing countries than in industrial countries. Economic inequality exasperates this phenomenon. Some argue that short stature due to economic status could be attributed to higher levels of stress in low-income families. Low-income is also associated with higher rates of obesity in developing and industrial societies where high-caloric, low-nutrient foods are cheapest.

Ideology and Beliefs have also been shown to influence growth. Families in Niger would rather keep their possessions important for determining rank, instead of selling them for money, because in this culture status is very important. In the US parents may opt out of forcing their children to eat healthy foods in order to maintain a peaceful dinner environment because here an emphasis is placed on having positive family dinners. In Tanzania children from monogamous marriages were taller and thinner than children from polygamous marriages.

Environmental Pollutant (toxicant) exposure has been associated with reduced height. Prenatal exposure to cigarette smoke and/or alcohol shows babies that are born smaller. Children with high blood lead levels have slower prenatal and postnatal growth and delayed puberty. Polychlorinated biphenyls (PCBs) can increase maturation rates in girls. Girls with higher levels of PCBs have earlier menarche, but there is little affect on overall growth patterns.

Recent Trends in growth patterns show that height and weight have increased in populations around the world. Over the last 100 years in Sweden, female height has increased by almost 5 inches and male height by almost 8 inches. This next part is a little unintuitive, but trends show that we are maturing earlier as well as faster. The age of menarche has decreased from 15-16 in the 19th century to 12-13 years old in most industrialized societies. Increases in leg length are higher than the increase in trunk length. European populations are now on average taller than Americans. While the height of populations in Oaxaca, Mexico has remained the same for 500-3000 years, during the last 30 they got a health center and secular trends have showed up in children’s growth patterns. Recent Mayan immigrants to the US have children that are approximately 4 inches taller. 70% of this height increase is attributed to longer legs.

Why are these trends happening though? The change in the last 150 years has happened too fast for it to be attributed to genetics. The reduction of infectious diseases could be a factor-improvement of world populations overall. Greater gene flow between populations could also be a factor. The increase in body size appears to be slowing and plateauing in affluent countries. A downside to these trends is that an earlier age of menarche has been deemed risk factor for breast cancer, heart disease, and type 2 diabetes. Obesity is becoming an ever-increasing problem around the world. About 67% of US adults are overweight or obese.


Nutrition and Disease throughout the Life Cycle

Parental Growth usually assessed by birth weight can give indications on how an individual will grow. Babies less that 5.5 lbs are considered to have a “low birth weight” which can result from prematurity, slow growth during gestation, genetics, or multiple births. During WWII women in Russia and the Netherlands were under siege from the Germans reducing the amount of food entering the cities. Birth weight decreased in these populations, with 50% of babies in St. Petersburg being born with low birth weight. An increase in maternal nutrition during pregnancy shows an increase in birth weight. However, if a woman has been malnourished her entire life, increasing nutrition during pregnancy is not enough to increase birth weight. Babies can adjust their metabolism to what they (and their mother) are experiencing during pregnancy. So if a woman is normally well nourished, but during pregnancy is malnourished, this cannot only make the baby be smaller, but also change the child’s overall metabolism. Maternal cues to the fetus including placental transfer of nutrients or hormones would be an epigenetic effect. Studies have shown that a women’s birth weight is a strong predictor of her children’s birth weight.

Infancy and Childhood Growth is more important, however, in terms of its affect on body size and health. Disruptions in the growth of children are the main cause of small adult body size.  Human milk is relatively low in fat and protein content indicating frequent nursing and slow rates of postnatal growth. Breast-feeding infants is very beneficial for developing infants. Other feeding methods do not provide anti-infective agents that help in the development of the baby’s immune system. These agents include antibodies against specific bacteria and viruses; white blood cells; and proteins, fats, and carbohydrates that convey antimicrobial action. Bottle-fed infants have higher rates of illness and mortality than breast-fed infants. It can be “argued that breast milk is the nutritionally ideal food for infants because it is the food that has evolved to meet their needs. “ Breast-feeding is associated with lower risk of ear, respiratory and gastrointestinal infections; sudden infant death syndrome; asthma; and reduced risk of obesity and diabetes in the children.

During the first few months of development, infant growth rates are consistent in poor and developed countries. However after the age of 4-6 months the growth rate in infants in disadvantaged circumstances decreases. By two years, there is a substantial different in height.  The slowing of growth is referred to as growth faltering. By 5 years old, children in poor countries fall below the 25th percentile for height. In rural Mali cultures young children are not encouraged to eat, and must fend for themselves. But in rural highland Peru children are given preferential treatment, and in times of food shortage are given food over adults. Growth faltering is not only nutritional but also caused by diseases.  Children and infants exposed to pathogens may experience more growth faltering.

What did you think of the Mali cultures?

Adolescent Growth is less affected by environmental factors due to the fact that this period is characterized by slower growth rates. In some environments rapid maturation is necessary due to high mortality rates.  Rapid maturation results in smaller adult body sized, but the individuals can reproduce at an earlier age. In these cultures there is a trade off between rapid maturation and small adult stature.

Catch-up Growth is a period of faster growth that follows a disruption. Turkana populations are initially below the 50th percentile and sometimes lower than the 5th percentile in height, but when they reach maturation they are on the normal standard. This can be explained by a longer growth period in these populations.

Is small body size an adaptation? It has been argued that when a human is exposed to low-nutrition environments they may cut their losses and remain smaller so that the resources that they have can go father. This would allow for more fit individuals that are smaller than their maximum potential.

Human height variation is a complex outcome of gene and environmental interactions. Narrowing down the cause of height to one factor is impossible, and when looking at height distributions you must take into account genetic history, environment, nutrition during development, social status, and cultural influences.



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.


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.


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.  


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?  


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.


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?


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?


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?




I'm super excited that my class was funded to do 23&me. I've been wanting to do it for the past two years, but I haven't gotten around to doing it. I'm most interested in discovering my ancestry. My family has been in the United States long enough that I don't know much of my heritage. (I can actually trace every side of my family back over 100 years in the same two adjacent counties in North Alabama).  There has been some circumstantial evidence that I may have Scottish in me, but that is the only European country I can name-despite my family being completely of European descent. And as every other white southerner would say, there is a rumor that my great-great grandmother was full-blooded Cherokee. I've always been fascinated by figuring out my ancestry, and having these results could give me some interesting clues.

The second part to 23&me is the health risks and traits it returns. I'm both excited and nervous about this. I don't really want to hear bad news. The things I'm most worried about are breast cancer (or any cancer for that matter) and Alzheimer's (or other forms of dementia). Both of my grandmothers have had a form of cancer, and I feel that I could be at high risk for breast or colon cancer. Something that worries me more than that though is the mental issues I may face down the road. My dad's mom and her family are also an interesting case with mental diseases. Of 6 children, 4 of the siblings (including my grandmother) have had some form of mental disease. One of my grandmother's sisters was put in a mental institute at age 20, and died there. Another sister is in the late stages of Alzheimer's, and will not be around much longer. My grandmother's brother has dementia that is getting worse with time. And my own grandmother's mind has gotten worse and worse, especially after my granddad died 3 years ago. With 4 out of 6 siblings having problems, it begs the question is it genetic? And if it is, what does that mean for me? I feel that there isn't a lot of prevention that can actually stop these mental diseases. Time will always win. So knowing now, years before it becomes an issue, just seems like torture to me. I'm very future oriented, but knowing that something bad is coming will bother me more than it will help me.

I really want to do 23&me. I'm super excited about the ancestry part, and a little apprehensive about the risks part. Talking about this to my class will be lots of fun, and I can't wait to see all the results.