Mechanisms of Evolution

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Mechanisms of Evolution
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I. Natural Selection Charles Darwin

• Charles Darwin (1819-1882) an English scientist
  considered the founder of the evolutionary theory
• Evolution is often referred to as Darwinism

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• Darwin studied many forms of life through the
  voyage of the Beagle
• Galapagos Islands was where Darwin studied a
  majority of the organism

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• Darwin's comparison of the animals of South
  America and the Galapagos Islands caused him to
  conclude that adaptation to the environment can
  cause diversification, including origin of new
  species

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The Galapagos Islands

• Darwin notes
• Island species varied from the mainland species,
  and from island-to-island
• Each island had either long or short necked
  tortoises depending on the island's vegetation

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The Galapagos Islands

• Darwin noted
• Finches Bill shapes are adaptations to different
  means of gathering food.

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• Galapagos finch species varied by nesting site,
  beak size, and eating habits

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The Theory of Evolution Darwinism

• We have discussed the 4 supporting evidences of
  evolution.
• Comparative anatomy
• Molecular Biology
• Biogeography
• Embryology

Today we are going to discuss the 4 mechanisms of
HOW Evolution occurs
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Outine 4 Mechanisms of Evolution

1. Natural Selection
2. Mutation
3. Migration
4. Genetic Drift

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1 Natural Selection

• Natural Selection AKA Survival of the Fittest
• A gradual, non-random process by which biological
  traits become either more or less common in a
  population

As you can see there is a variation in the
phenotype of these beetles Green or brown
?
?
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Genetic Variation Genetic differences within a
population.
The genetic variation in this scenario are the
genes that code for the color of the beetle.
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3 Types of Natural Selection that Act on
Variation

• 1. Stabilizing natural selection that favors
  average individuals

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3 Types of Natural Selection that Act on
Variation

• 2. Directional selection natural selection
  that favors an extreme form of a trait

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3 Types of Natural Selection that Act on
Variation

• 3. Disruptive selection individuals w/ either
  extreme form of a trait

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2 Mutation

• Mutation change in a gene alteration of a
  nucleotide sequence.

EX A mutation causes two green beetle parents to
have a brown beetle
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3 Migration

• Migration Movement of some individuals to
  another population

Gene Flow transfer of alleles from one
population to another population through
immigration of individuals . This disrupts allele
frequency.
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4 Genetic Drift

• Genetic Drift some individuals may by chance and
  not because of fitness leave more descendants
  and therefore pass on their genes.

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The Evolution of Species

• Species organisms that look alike can
  interbreed to produce fertile offspring
• Speciation evolution of a new species.

NOTE Organisms within the same species have
reproductive success ( ability to pass genes onto
the next generation in a way that they too can
pass on those genes.)
Mule
He can not have offspring because his parents are
two different species ?
Donkey
Horse


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So how do new species come about?
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Physical Barriers Cause Speciation

• 1. Geographic Isolation a physical barrier
  divides a population

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• 2. Reproductive Isolation the inability of
  organisms to mate and breed fertile offspring
• Genetic material becomes so different
  fertilization can not occur
• Behavior mating seasons are different

These Bowerbirds have different mating seasons
and rituals. These 2 factors contribute to
Reproductive Isolation
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Does evolution happen fast or slow?
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Both!
Speciation Rates - the time it takes for
evolution to occur. 2 Theories 1
Gradualism idea that species originate through
a gradual change of adaptations
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• 2. Punctuated Equilibrium things staying the
  same for a period of time then rapidly changing
  due to a catastrophic event.

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There are TWO types of Evolution
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• 1 Divergent Evolution accumulation of
  differences between groups which can lead to the
  formation of new species

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• 2 Convergent Evolution organisms not closely
  relate, independently evolve similar traits (to
  adapt to similar environments.)

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Genetics Determines Evolution

• Gene Pool All the alleles in a populations
  genes. In other words every form of a trait
• Allelic Frequency the of any specific allele
  w/in a gene pool

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• Genetic Equilibrium allele frequency remains
  the same over generations
• Populations in genetic equilibrium are not
  evolving
• Factors that affects genes can affect equilibrium
• 1. Mutations negative, positive
• Negative more than likely causes death
• Positive may be beneficial

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Trait Variations differences in Organisms

• Increases or decreases an organisms chance of
  survival
• Inherited and controlled by alleles
• Allelic frequencies in a populations gene pool
  will change due to natural selection

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• C. Patterns of Evolution
• 1. Adaptive Radiation ancestral species
  evolves into an array of species to fit a
  particular environment.