Anthropology Week 3 Notes
Anthropology Week 3 Notes ANTH 160
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This 9 page Class Notes was uploaded by Amanda Notetaker on Thursday September 8, 2016. The Class Notes belongs to ANTH 160 at University of New Mexico taught by Dr. Tanya M. Meuller in Fall 2016. Since its upload, it has received 5 views. For similar materials see Human Life Course in Anthropology at University of New Mexico.
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Date Created: 09/08/16
Anthropology 160.001 The Human Life Course Week 3 Week 3 Readings: Trivers: Chapter 3, Elementary Social Theory, pp. 41-66. (Learn) (Tuesday, Thursday September 6, 8): Reciprocal Altruism AUTHOR NOTE: Since the readings themselves are on my university’s website specifically I realize it does not do much good to simply post the author’s last name and a few page numbers. My notes are currently relaying the lecture information that sometimes does not cover the readings. Next week we get more in depth with chapters in the textbook, Why Sex Matters. The book is available on amazon. 9/6 Continuing lecture 3… Intensity of Selection Selection pressure: factors that influence the rate of natural selection and evolution For humans it would take only 10,000 years for a trait with a 1% disadvantage to change from 99% frequency to less than a 1% frequency as long as selection is consistent and unidirectional. Even trivial traits can be associated with reproductive success o Head roundness and differential survival No trait is adaptive in all environments Genotype, Phenotype, and Heritability Phenotype: the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment . Genotype: the genetic make-up of an individual; actual code of genes How does genotype translate into phenotype? Though the phenotype of some traits is closely tied to genotype, many are also influenced by the environment. Example: height and weight have a very strong genetic component, however dietary composition can strongly influence the results. Heritability and phenotype: The biggest problem in accepting an evolutionary view of behavioral variation Behavioral variation can’t be heritable because so much of it is socially learned (cultural) or contingent on conditions that change from moment to moment. Gregor Mendel (1822-1884) -Father of modern day genetics Mendel realized some traits were visible in offspring while in the next generation some seemingly disappeared. If you keep the chart going however, you see them reappear and can map the variance in many future generations. Conclusions: 1. There are two alleles for each trait 2. Parent contributes only one of their two alleles to an offspring 3. Alleles are contributed with equal probability 4. Alleles for different traits segregate independently = Principles of segregation = Principle of independent assortment Incomplete Dominance: expression of a phenotype that is intermediate between those of the parents. Example: When one parent produces red flowers and the other white, expected offspring should be either red or white. However, once bloomed, the offspring were a shade of pink. *We see this same concept in sickle cell anemia: heterozygotes have no disease but there is intermediate sickling when blood cells are subject to really low oxygen levels. Co-dominance: the full phenotypic expression of both alleles in the heterozygous condition Example: When the male and female create the offspring, both dominant genotypes are passed down, creating a hybrid phenotype. Heritability and genotype: REMEMBER : genotype refers to the genetic make-up of the individual. During meiosis (gamete formation), genetic material is copied and enclosed within the gametes given perfect replication (DNA copying), this genetic material passed on to subsequent generations should be identical (though variation through sexual reproduction arises). NOTE : each gamete does not have identical genes since each parent only passes on one of two copies of each allele with equal probability, but composition of genes should not change. Sources of variation 1. Mutation –imperfect copying of DNA strands a. In humans the mutation rate is 10^-4 to 10^-6 per gene per generation. b. This implies since we have about 30,000 genes, there is one mutation per every three offspring born. *In most cases, a single mutation is functionally neutral Significant mutations observable defect 2. Recombination –essential part of sexual reproduction a. This process takes place every generation and the offspring produces a new combination. 3. Crossing over –new chromosomal combinations; variation a. Chromosomes are mixed with pieces drawn from Grandmother and Grandfather to create a new chromosome that neither had. b. During recombination the genes still stay in the same place and the same order, but homologous chromosomes, which are paired, can swap genes. c. Thus the chromosome 13 that gets passed on to ones offspring contains a mix of genes from chromosome 13 in grandmother and grandfather. Random recap Components of fitness: 1. Survival 2. Reproduction 9/8 Continuing from lecture 3 Can Human Behavior Evolve? -Human behavior seemingly changes on a whim, is there a way it has evolved systematically? The Dung Fly Story –Geoffrey Parker Dung fly females mature a large quantity of eggs and store them until they are ready for oviposition Females look for suitable dung to place larvae in; they are cautious in the way they place the larvae o Based on competition with other females, status of dung, etc. Sperm is stored in the female –females have no problem finding males for sperm retraction Males flock to dung o 4-5 males to every female Females arrive Male sights female, leaps, mounts, orients and mates immediately o The male penis is like a plunger that forces out old sperm o Success is partly based on how long the male copulates Active competition and aggression among males even while male is attached to female and she is ovipositing What is a male to do about the competition? o 3 types of females: Arriving Copulating Ovipositing o Males have highest likelihood of success with arriving females o Males are most likely to be successful by positioning themselves in the grass area near the dung Diminishing returns curve: Your value/payoff is dependent on where you lie on the curve Your tangential value is the highest likelihood of success How long to mate? Diminishing returns to time spent in copulation. There is a tradeoff between the proportion of the females eggs fertilized and the possibility of finding another female Given an average expected search time for the next female, optimum amount of time to spend in copula with the female The longer a male mates with a female the more sperm from the previous male he displaces, but at a diminishing rate. Flies spend very close to the optimum. Optimal copulation time is around 45 minutes o On average they copulate for 35 minutes Can we show that natural selection can act on behavior? William Cade observed that shorter caller male crickets had a higher mating rate. After only one generation, there were significant differences between long and short caller males. Those differences became increasing large with each generation of selection. How predictable is environmentally flexible behavior? The case of the blue gill sunfish Establishes territory and defends it from any other males Two types of males: o Large male (parental) o Satellite male (cuckolders) NOTE: The cuckolders resemble the blue color of the female fish while the parental fish is much larger and spotted Parentals delay maturation until 7 years of age. They build nests to protect offspring and attract females. Females release eggs by nest and males release sperm to fertilize eggs, and males guard the eggs. Cuckolders start reproducing at age 2 and provide no care. They wait near a parental male’s nest and dart in ejecting sperm during the spawning with the parental male; thus gaining matings and parasitizing the care of parental males. The payoff to cuckolders depends on the environment. In weedy areas, cuckolders do better when they are alone. They can hide and if there are few other cuckolders, most of the additional fertilizations are theirs. When there is low cover, they do better in bigger numbers, because they can distract the bigger parental males. The number of cuckolders systematically corresponds to % cover in predicted fashion. It is also probably the case that many cuckolders become parentals after they grow. Recap: Genotype: combination of genes Phenotype: characteristics exhibited by living organism *Phenotype can vary according to environment, even with constantly held genotype STATURE EXAMPLE: perhaps 95% genetically determined. It can bet that everyone here had adequate nutrition during development. If the room were filled with representative sample of the world’s population, would have to change the percentage determined by genes, perhaps down to 50% or less. Nutritional differences come into play. Cannot make statements about what percentage is environmentally or genetically determined without specifying what population and what environment. Concepts to take away from the examples today : Evolved reaction norms –response to given environmental and personal conditions The phenotype can be changed based on environmental input The environment turns genotype into phenotype then selects among phenotype *Nutrition is very important in mediating phenotype Phenotypic Plasticity: the ability to change reaction pattern to the environment that has evolved rather than a single invariant phenotype The pattern associated with different environments is called the reaction norm. This is also referred to as a facultative phenotype. Reaction norms are expected to be adaptive since they evolve by natural selection. EXAMPLE: People who live at high elevations have very high red blood cell densities that are apparent in their cheeks. This is an adaptive reaction norm. Natural selection favors a phenotype generating mechanism!!!
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