PROCESSES OF EVOLUTION 1. What are species? 2. What are the processes of evolution? 3. How do these...

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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?

Transcript of PROCESSES OF EVOLUTION 1. What are species? 2. What are the processes of evolution? 3. How do these...

Page 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.

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?

Page 2: 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.

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)

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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!

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2. WHAT ARE THE PROCESSES OF EVOLUTION?

EVOLUTION = changes in allele frequency through time

1. MUTATION2. NATURAL SELECTION3. GENE FLOW4. GENETIC DRIFT

Page 5: 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.

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

a phenotype

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Body cellsSex cells

Crossing Over

Recombination

Mutations might happen!!

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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

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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

Page 9: 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.

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 PARTICULAR ENVIRONMENT at a PARTICULAR TIME

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Darwin’s Finches:Example of Natural Selection

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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

Page 12: 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.

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

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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?

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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

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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!

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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

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Bottleneck:Example of Founder Effect

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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!

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Sickle Cell Anemia:Evolutionary Processes In

Action

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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?

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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?