Week 5 ANTH 1001
Popular in Introduction To Biological Anthropology
Laura Castro Lindarte
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Popular in Biology/Anthropology
This 7 page Class Notes was uploaded by Laura Castro Lindarte on Thursday September 29, 2016. The Class Notes belongs to ANTH 1001 at George Washington University taught by W. Andrew Barr in Fall 2016. Since its upload, it has received 16 views. For similar materials see Introduction To Biological Anthropology in Biology/Anthropology at George Washington University.
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Date Created: 09/29/16
September 26, 2016 Human Variation (P. 1) ● Things that didn’t covered last class: ○ Just because two organisms are ali oes not mean that they are closely related ■ Some things like fur are from common ancestor (primitive traits) NOT HELPFUL TO LOOK AT RELATEDNESS a. Primitive = symplesiomorphies ■ Better to look at shared derived traits (come after ancestor) when want to know if related a. Derived = synapomorphies ● Before 19th century, biological anthropology looked at human var racist past) ● Concept of race more SOCIAL THAN BIOLOGICAL ● How to break down species? ● Humans are phenotypically diverse ○ Our perception of it has subjective bias (humans are good at seeing different in humans) ■ Historical idea of race based on geography is not okay ■ We exaggerate our differences ● Humans are NOT very genetically diverse ○ We see so many differences because of social reasons (good at it) ○ Chimpanzees show two to four times more genetic diversity than humans ○ Why? 1. Relatively recent BOTTLENECK event in human history 2. Gene flow is vast in human population compared to others a. Due to migration ● “Race”: a group of populations hare certain characteristics that make them distinct from others ○ Biological and cultural differences ○ Biological term different than social everyday term ● Some variations are geographically struct people will mate with those close to them) ○ Relationship between geography reflect gene flow ○ True for cultural and physical variations ○ BUT GEOGRAPHICAL CATEGORIES FOR RACE ARE NOT ACCURATE ● Apportionment of human diversity (Lewontin, 1972): ○ How much is variation is seen across geographical regions and how much within region? ■ Only 10% of diversity see between large geographical regions, 85% seen WITHIN POPULATIONS ● Term “race” is a typological and arbitrary concept which assumes that human variation can be classified in distinct gro NOT ACCURATE) ● Skin color is what has gotten most attention ○ If you look at few specific populations it would be easy to categorize skin color into light, medium and dark BUT NOT THAT SIMPLE WHEN YOU LOOK AT MANY DIFFERENT GROUPS (will see whole array) ○ Categorizing humans by skin color is arbitrary, might get some aspect but not all variation ● Clinal distribution: patterned distr cross a geographical gradient ○ One area has most then as you get away from it there is gradual change ○ Ex: ABO blood and skin color ○ Continuous, no break ● Poor concordance between different traits ○ Each trait is spread throughout globe in different one population won’t always have particular trai o can’t stereotype) ● Biology of skin color: ○ Skin is large organ with different functions and layers ○ Outside layer is epidermis made out eratinocytes (largest number, made in bottom of epidermis and move outward, roduce keratin which gives water protection) and melanocytes (not as many, creates pigment melanin) ■ Melanin is one factor that gives pigment, gets deposited throughout epidermis ○ Color of skin depend on: ■ Hemoglobin: hat allows blood cells to transfer oxy ives red tint ■ Keratin: different in amount of ke ives yellow tint ■ Melanin: AJOR DETERMINANT, dark pigment so the more melanin that is produced the darker it is, the less melanin present the more the other pigments are visible a. Number of melanocytes is about same, b ut amount of melanin produced and deposited in keratinocytes b. POLYGENIC TRAIT, d ark: lots of production of melanin, light: less melanin produced ○ Skin color follows clinal distrib arker when closer to Equator and lighter when further from Equator looking at indigenous populations) ■ Not as harsh in New World because humans not there until recently (less time to adapt) ○ UV radiation is higher in Equator and less in poles ■ Damage DNA in cells ■ High energy and non-visible radiation in sunlight ■ Melanin absorbs UV and prevents it more damaging DNA ■ Degree UV penetrates the skin is inversely proportional to melanin ○ 3 main theories of natural selection and UV: 1. Dark skin is adaptation to skin damage and skin cancer 2. Nutrient photolysis: folic acid 3. Vitamin D synthesis ○ Skin damage: ■ Sunburn: facilitates infection, impairs thermoregulation, permanent damage ■ Skin cancer seen more in light sking living in tropical areas, l ow in dark skin population a. Places like Africa and Australia are hotspots for skin cancer in immigration population ■ Natural selection for dark skin in tropical a ark skin is more fit ○ Nutrient photolysis: ■ Chemical molecules important to metabolism are sensitive to UV radiation and will undergo decomposition (photolysis) ■ Folic acid: i mportant to central system development, DNA replication and cell division a. Deficiencies can lead t regnancy complications, neural tube effects, impaired sperm productio hich impact REPRODUCTIVE SUCCESS b. Photosensitivity of these nutrients suggest that it is important to have rotection from the depleting effects of UV radiation ■ Dark skin more fit because decreases folic acid ○ Vitamin D synthesis: ■ Essential for calcium metabolism and normal bone and tooth development a. Difficult to get in normal diet ■ Primary source of vitamin D is synthesis in skin a. Made through interaction of UV and cholesterol-like substance i. Dark skin requires six times as more to make vitamin D in sun ■ Rickets: disease in kids caused itamin D deficiency that causes impaired mineralization of developing bones and teeth a. Negatively impacts reproductive success and driv election for light skin far from Equator to guard for vitamin D deficiency ○ MORE MELANIN FOR NEAR EQUATOR AND LESS FAR FROM IT ■ Humans originated in Africa so were probably dark skin, only recently have humans began to live in high latitude areas ■ Only recently have populations in northern latitudes evolved lighter skin color, due to relaxed selection of dark skin and direct selection to absorb more UV to make vitamin D September 28, 2016 Human Variation (P. 2) ● Why is race not a good representation of biology? ○ More variation seen within populatio ot between populations ○ Variation in human is GRADUAL WITH CLINAL DISTRIBUTION ■ Variation is not seen in clusters around globe ■ Ex: skin color changes gradually depending on how far you are from the Equator ■ Variation is geographically structured but in clinal distribution ○ “RACIAL” groups don’t describe variation ■ Better to look at environmental pressure to explain diversity ● Sickle Cell Anemia: ○ Crescent shape of red blood cell ○ Caused by POINT MUTATION (single letter swap out for another) in ancestor’s gamete i emoglobin gene which allows blood to transfer oxygen and influences shape of red blood cell ■ Point mutation causes shape of hemoglobin to change ○ Individuals with sickle cell anemia have wrong red blood cell shape ■ Normal red blood cell shape allows it to go through all body even small vessels but ickle cells can not go through because get stopped and PILE UP leading to blood clots ■ Sickle cells also more fragile, can’t carry oxygen as well ○ HbA = normal, HbS = sickle, genotypes: HbA HbA (homozygous normal so no risk of disease), HbS HbS (homozygous sickle so have disease but can be treated with medicine, if not medicine available then disease can be decreased so not wanted in natural selecti bA HbS (heterozygous, incomplete dominance (codominance) so have normal and sickle cells, have little symptoms of disease) ■ In tropical areas, fitness level of HbS HbS is about 0 to 33% of normal people, HbA HbA is 85% ○ Pockets in Africa, India and Middle East with lots of sickle cell anemia ■ Natural selection keeps disease because it is good to be heterozygous HbA HbS ■ Areas with high malaria are same with those with more sickle ■ Heterozygous have resistance to malaria so HETEROZYGOUS IS MORE FIT THAN BOTH HOMOZYGOUS DUE TO MALARIA a. Heterozygous fitness is 100% ○ Balance polymorphism: stable polymorphism, natural selection prevents any alternative alleles from being fixed or disappearing ■ Happens in all cases that it is fit to have heterozygous ■ Heterozygous advantage: more fit to be heterozygous ● Lactose intolerance: ○ ALL MAMMALS DRINK MILK IN INFANCY ■ Lactose found in milk and made of glucose and galactose so mammals have lactase to break it down ■ Most mammals lose ability to produce lactase after weaning ○ Adult lactose intolerance is NORMAL in mammals ■ When you are intolerant you are unable to break down lactose so bacteria break it down which leads to gas ■ Loose ability to produce lactase once out of infancy stage because no longer need it ○ LCT*P (dominant) = lactose persistence, LCT*R (recessive) = lactose intolerant ■ VARIES IN DIFFERENT HUMAN POPULATION ○ Lactose tolerance evolved by recent natural selection favoring lactase persistent in CULTURES WHERE MILK IS PART OF WAY OF LIFE ■ In Africa: fulani have 22% because historically depended on cattle so good to persistence, not seen in Bantu ○ Adult lactase persistence aused by mutation resulting in permanent production of lactase ■ Neutral in no dairy cultural but beneficial in dairy cultures so common ● Body size and shape: ○ Bergmann's Rule: individuals in colder habitats tend to have larger body size ■ More in inside so less heat lost through body surface ■ BIG IN COLD, SMALL IN HOT ■ Seen in bear size: tropical bears are smaller, American brown bears are a little bigger, grizzlies are bigger than that and polar bears in Arctic are biggest ○ Allen’s Rule xtremities tend to be longer in warmer h ecause serve to dissipate heat through them ■ Antelope Jackrabbit has longer legs and ears because warmer, Arctic hare have smaller ears because cold ○ BOTH RULES APPLY TO HUMANS ■ Those in Arctics have longer body but short extremities, those near Equator have shorter body and longer extremities (African Dinka v. Inuit) ■ Can apply to different species and within species ● High Altitude Adaptations: ○ Lower oxygen availability in higher altitudes ○ Not less oxygen percentage just that air is less dense so molecules are further apart o less molecules come in during a single breath ○ When not adapted you experience ltitude sickness ○ Population in high altitude for generations have different adaptations ■ Andean Altiplano: more hemoglobin, different lung size and shape to have more lung capacity ■ Tibetan Plateau: low hemoglobin, higher respiration rate and increased blood flow ■ Different adaptations between two populations but all help with the higher latitude ● Adaptations not climatization ○ If you are not from there you won’t have the adaptations
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