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PROCESSES OF EVOLUTION

PROCESSES OF EVOLUTION. 1. What are species? 2. What are the processes of evolution? 3. How do these processes interact to bring about evolution as we understand it today?. 1. SPECIES.

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PROCESSES OF EVOLUTION

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  1. PROCESSES OF EVOLUTION 1. What are species? 2. What are the processes of evolution? 3. How do these processes interact to bring about evolution as we understand it today?

  2. 1. SPECIES • Population of organisms whose members can, under natural circumstances, freely interbreed with one another and produce fertile offspring Examples: Dogs & Wolves = can (but often do not) produce fertile offspring, so now in same species canis lupus Horses & Donkeys = produce mules, but infertile Lions & Tigers = can produce fertile offspring, but never in the wild! (different behavioral niches)

  3. Why is Distinction among Various Species so Vague? • Species emerge OVER TIME! • All species evolve at different rates! • Humans are making up the rules/categories!

  4. 2. WHAT ARE THE PROCESSES OF EVOLUTION? EVOLUTION = changes in allele frequency through time • MUTATION • NATURAL SELECTION • GENE FLOW • GENETIC DRIFT

  5. Allele = variants of a gene, carry different instructions for development of a phenotype

  6. Mutations might happen!! Sex cells Body cells Crossing Over Recombination

  7. 1. MUTATION • Any change in the genetic code • Bioanthropologists are interested in mutations in the sex cells (gametes) • Changes allele frequency • Adds GENETIC VARIATION to a species gene pool

  8. Trisomy 21 = Example of Mutation • Chromosomal mutations = mutations of whole or large portion of chromosome • 3 copies of chromosome 21= Trisomy 21 or Down syndrome • During MEIOSIS, a pair of chromosomes did not segregate

  9. 2. NATURAL SELECTION • Definition = Evolutionary change based on the differential reproductive success of individuals within a species • When is an individual successful? When s/he has a phenotype (trait) that is important for the adaptation of a particular species to a PARTICULARENVIRONMENT at a PARTICULAR TIME

  10. Darwin’s Finches:Example of Natural Selection

  11. Beaks and Body Size(Rosemary and Peter Grant’s research) • 1977: Year-long, severe drought on a small Galapagos Island • Insects disappear, only tough seeds left • 1978: 14% of finches made it • Survivors: 5-6% larger than those who died, longer & deeper beaks

  12. Would the increased body & beak size be passed on to offspring? • Next generation: yes! Larger body and beak size • Several generations later (environmental conditions back to normal): beak and body size decreased toward previous dimensions

  13. What do we learn? • The useful variation (large beaks & bodies) was ALREADY present! (not “acquired”) • Adaptation to change is LUCK! (90% of Earth’s species are extinct!) • NS does NOT produce change in a particular direction & does NOT ensure survival of a species! • This idea can be uncomfortable! What if life is unpredictable?

  14. 3. GENE FLOW Definition: Genes within a species “flow” among the populations of that species, changing allele frequencies & adding genetic variation to the whole species How does this happen? Members of different DEMES interbreed & new genetic combinations may show up in offspring Demes: Breeding populations separated by environment

  15. Immigration & Sex:Example of Gene Flow • Today, more people are mobile • We find mates from different parts of the world • We add variation to human gene pool!

  16. 4. GENETIC DRIFT Definition: Genes within a species “drift” when a population within a species splits. Each new population exhibits a NONREPRESENTATIVE sample of the genes of the original Fission: Splitting of a population Founder Effect: When one of the new populations is drawn from a small sample of the original population, it will be DIFFERENT genetically

  17. Bottleneck:Example of Founder Effect

  18. North American Hutterites:Example of Genetic Drift • 300 original Hutterites founded colonies in 1874 & 1875 • 90 people contributed genes to future generations • Today, about 35,000 Hutterites can trace genes back to less than 100 ancestors!

  19. Sickle Cell Anemia:Evolutionary Processes In Action

  20. Group Exercise:Sickle Cell Anemia 1. How did Sickle Cell Anemia come about? 2. What happens when someone is homozygous (SS) for the Sickling Trait? 3. What does it mean that heterozygotes (AS) have an adaptive advantage in malarial areas? 4. How is the connection between sickle cell and African Americans an example of the founder effect?

  21. Group Exercise:Sickle Cell Anemia 5. How can people of European American ancestry have sickle cell? 6. How is the story of sickle cell an example of the holistic perspective of anthropology?

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