PROCESSES OF EVOLUTION

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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?

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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
• MUTATION
• NATURAL SELECTION
• GENE FLOW
• GENETIC DRIFT

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Allele variants of a gene, carry different
instructions for development of a phenotype
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Mutations might happen!!
Body cells
Sex cells
Crossing Over Recombination
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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

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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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Darwins FinchesExample of Natural Selection
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Beaks and Body Size(Rosemary and Peter Grants
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

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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 Earths
  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 SexExample 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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BottleneckExample of Founder Effect
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North American HutteritesExample 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 AnemiaEvolutionary Processes In
Action
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Group ExerciseSickle 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 ExerciseSickle 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?