Anthropology Test Two Notes - Polymorphism is the interaction between natural selection and mutation- Polymorphism : situation where there exists two or more alleles for a gene and at least two alleles have frequency greater than 1%- 28% of genes are polymorphic- Polymorphism is due to natural selection acting on genetic variations caused by mutation- Balanced polymorphism : situation where there exists two or more alleles for a gene, and atleast two alleles have frequency greater than 1%. Due to heterozygotes having higher fitness than homozygotes- The frequency of the sickle cell allele is 5%-15% in some areas.- Hemoglobin consists of two alpha and two beta polypeptide chains- Each alpha chain has 141 amino acids; each beta chain has 146 amino acids- Sickle cell hemoglobin due to one point mutation affecting one amino acid in beta chain- Malaria is caused by parasite transmitted between individuals by mosquito- Heterozygotes for sickle cell have lower rate of malarial infection compared to homozygotes for normal hemoglobin- Heterozygotes for sickle cell have selective destruction of red blood cells- Uninfected RBCs do not sickle; infected RBCs sickle and kill parasites- Heterozygotes con conjointly supply oxygen to tissues and suppress parasitic proliferation- In malarial environment, heterozygotes for sickle cell have natural selective advantage over homozygotes for normal hemoglobin and sickle cell. Because of heterozygote advantage, alleles for both normal and sickle cell hemoglobin are maintained at high frequencies; this is balanced polymorphism- Evolution of balanced polymorphism for sickle cell- Spread of slash-and-burn agriculture is related to natural selective advantage of sickle cell allele- Thalassemia and G-6-PD deficiency are at polymorphic levels in some populations- Natural selection is opportunistic; selection acts on the phenotypic/genotypic variability thatexists in populationThursday, 26 September 2013“Human Bio-cultural Adaptation”- Examples: sickle cell and other red blood cell variants; lactose sufficiency- Lactose tolerance and intolerance- Lactase – enzyme that allows you to digest lactose, which is a sugar in milk- Lactose intolerance – deficiency in lactase- Symptoms: diarrhea, nausea, abdominal cramps, gas- Humans can digest milk as babies, but most of us lose the ability after weaning.- Adults in some populations are lactose tolerant.- Populations with long histories of dairying are typically lactose tolerant- Mutation for ability to digest milk as adults would have provided a natural selective advantage- Human Variation- Our species is polytypic.- Polytypism : phenotypically different populations in a species- Polytypism is result of diversity of environments that we inhabit.- Our populations diversify because of natural selection, but our populations remain within a single species because of gene flow.- Race: not a biologically useful grouping of humans- Not useful in terms of evolutionary studies- The appropriate unit of evolutionary study is population.- It doesn’t tell you information. Also, it focuses on differences rather than similarities.- In science, the point of grouping is that the similarities are magnified.- Human Adaptation- Adaptation : change in the structure of a gene pool as a result of natural selection- Evolutionary perspective: result of natural selection- Human variation perspective : any beneficial modification that relieves environmental stressand enhances survival of individuals- Types of adaptations (in hierarchical order)- Behavior (learned)- Short-term (reversible) acclimatization- Shivering of the body is proof that heat is being produced.- Tanning- Hemoglobin at altitude- Developmental (irreversible) acclimatization- Genetic (result of natural selection)- Acclimatization as adaptation – acclimatization occurs at the level of the individual- Demonstrates the plasticity of human response to environmental stress- We have a lot of different ways of adapting, flexible.- All humans are capable of having these responses.- Acclimatization can be short term and reversible, or developmental and irreversible- Skin Pigmentation- Pigment is melanin.- Melanin is produced in melanocytes, which are in epidermis of skin- Melanin is packaged into granules called melanosomes.- Melanosomes are transferred to keratinocytes, which are also in epidermis- Melanin functions to block ultraviolet radiation from penetrating skin and damaging DNA.- Genetic similarities between heavily and lightly melanized individuals- All people have about the same number of melanocytes.- Genetic differences between heavily and lightly melanized individuals- Compared to lightly melanized individual, heavily melanized individual- Produces more melanosomes- Has larger melanosomes- Melanosomes are more dispersed in keratinocyte- Natural selective advantage to variation in skin pigmentation- Dark skin pigmentation- Adaptive in areas of intense ultraviolet radiation- Melanin functions to absorb ultraviolet radiation- Reduces likelihood of skin cancer and degradation of folate- Light skin pigmentation- Adaptive in areas of low ultraviolet radiation- Allows sufficient synthesis of vitamin D- Reduces likelihood of rickets- Human adaptation to low temperature environments: body shape- Bergmann’s Rule: body mass is higher in areas with lower temperatures- Allen’s Rule: length of arms and legs is shorter in areas with lower temperatures; x3/x2 mass/area- Human adaptation to low temperature environments: metabolism and blood flow- Populations living low temperature environments show an “extremities” adaptation:- Higher basal metabolic rate - Efficient vasoconstriction; maintain higher temperature of fingers and toes- Vaso means “blood.”- Constriction of blood vessels- Populations living in high temperature environments show a “hypothermic” adaptation- Lower basal metabolic rate - Adaptation to low temperature environments- Adaptations to low temperature environments by body shape, metabolism, and blood flow are developmental (irreversible) acclimatizations.- Adaptation to high altitude- Hypoxia (i.e. low atmospheric oxygen levels) is a stress of high altitude- Delivery of oxygen to tissues- Oxygen transfers between “compartments” of the body by diffusion.- lungs -> blood -> cells- Diffusion – movement of gas from area of higher concentration to area of lower concentration- Two variables influence rate