Mechanisms for Evolution

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Mechanisms for Evolution

• Lamark vs. Darwin

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Differing Viewpoints

• Charles Darwin
• Characteristics among members of a species vary.
• Only individuals with the characteristics best
  suited to the environment will survive to
  reproduce.
• Over time characteristics will increase in the
  population.
• (Now called Natural Selection)

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Differing Viewpoints

• Jean Lamark
• Evolution occurs through the use and disuse of
  physical features.
• Over an organisms lifetime features will
  increases by use or decrease by disuse.
• These traits are than passed down to their
  offspring.

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Lamark vs. Darwin
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Natural Selection

• Process by which populations change in response
  to their environments.
• Key components of natural selection
• Genetic Variation
• Competition and Struggle for existence
• Survival of the fittest (Variation is Selected)
• Increased frequency of best traits (Variation is
  inherited)

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Requirement 1 Genetic Variation

• Exists within a population through
• Meiosis genetic variation is increased during
  crossing over
• Mutations- spontaneous changes in DNA
• Genetic Recombination occurs during sexual
  reproduction and provides endless source of new
  variations

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Requirement 2 Struggle for Existence

• Every organism must constantly fight for limited
  resources (food, water, mates) and escape from
  predators in order to survive long enough to
  reproduce.

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Requirement 2Reproduction Leads to Competition

• When conditions are favorable organisms tend to
  produce many offspring.
• When resources become scarce competition occurs.

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Requirement 3Survival of the Fittest

• Individuals best suited/adapted to their
  environments have the best chances for survival
• Those individuals Reproduce more often and pass
  those good traits that allowed survival on to
  their offspring.

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End ResultIncreased frequency of best traits

• Over time, good traits appear more in a
  population because more individuals survive and
  reproduce.

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Examples of Natural Selection

• Sickle Cell Anemia
• Hereditary disease that affects hemoglobin
• Protein in our blood that carries oxygen
• 1/500 have Sickle Cell Anemia in US
• 1/100 have Sickle Cell Anemia in Central Africa

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• Malaria is a warm climate disease caused by a
  parasite that is transmitted by mosquitoes.
• Causes death if not treated.
• People with sickle cell anemia are more resistant
  to malaria

• AA normal blood (no resistance)
• Aa both normal and sickle shaped blood
  (resistance)
• aa all sickle shaped blood (resistance)

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Types of Natural Selection

• Balancing Selection (Stabilizing Selection)
• When selective pressures select against the
  two extremes of a trait.

Aa
aa
AA
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Another Example

• The Peppered Moth
• White or black and sits on the bark of trees
• Pray to birds

• Industrial revolution
• Increased pollution
• Killed lichens on trees
• Trees covered in lichens appear more white while
  trees without lichens appear dark

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What Happened?

• No pollution

• Lots of Pollution

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Try It.

• http//www3.district125.k12.il.us/faculty/nfischer
  /Moth/default.htm

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• 2) Directional Selection
• When selective pressures are against one
  extreme.

Black Moths
White Moths
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Another Example

• Imagine rabbits with fur that can either be
  black, grey, or white (due to incomplete
  dominance)
• The environment consists of black rock
  outcroppings, and white snowy tundra.
• Animals that are born with the heterozygous grey
  coats are going to be spotted easily by their
  predators. Animals with black or white fur are
  likely to survive and reproduce more offspring
  than gray rabbits.

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• 3) Disruptive Selection
• When selection acts against individuals in the
  middle of the trait.

White rabbits
Grey rabbits
Black Rabbits
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Adaptations

• An adaptation is an physical structure,
  physiological process or behavioral trait of an
  organism that has evolved over a period of time
  by the process of natural selection.
• Adaptations increase the reproductive success of
  the organism.

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Adaptations

• Organisms that are adapted to their environment
  are able to
• obtain air, water, food and nutrients
• cope with physical conditions such as
  temperature, light and heat
• defend themselves from their natural enemies
• reproduce
• respond to changes around them

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Types of Adaptations

• 1) Morphological structures are adapted to
  specific needs and environments.

Floating Leaves
Floating Leaves
Turtles shell
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• 2) Behavioral Adaptations based on behavior

Bird Migration
Living in herds/schools
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• 3) Physiological Adaptations Adaptations on a
  molecular level
• Things inside the body vs. outside

Poisons- Dart Frog
Bioluminescent deep sea
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Speciation

• If a species changes enough that it can no longer
  interbreed with the original species a new
  species can form.

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Types of Reproductive Isolation

• Reproductive Isolation-If a population becomes
  isolated and cant interbreed, changes can
  accumulate and a new species can form
• Three Types
• 1. Geographical Isolation
• 2. Temporal Isolation
• 3. Behavioral Isolation

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1) Geographical Isolation

• Separation by land forms or physical features
• Examples Rivers, mountains, islands

• Darwins Finches
• Galápagos Islands had different environments
• 14 species of finches arose by speciation from a
  single South American species.
• Populations of finches can no longer interbreed.

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Finches Beaks
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2) Temporal Isolation

• Separated by time of day or year reproduction
  occurs
• Examples gamete exchange during different
  seasons

Frogs Rana aurora - breeds January - March Rana
boylei - breeds late March - May
Fruit Flys Drosophila persimilis - breeds in
early morning Drosophila pseudoobscura - breeds
in the afternoon
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3) Behavioral Isolation

• Separated by behavior
• Examples Bird/frog calls, different courtship
  behaviors, lighting patterns of lightning bugs.

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Patterns in Evolution

• Convergence Unrelated organisms develop similar
  traits. Different geographical areas sometimes
  exhibit groups of plants and animals of
  strikingly similar appearance, even though the
  organisms may be only distantly related.

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Patterns in Evolution

• Divergence two related species become
  increasingly different. Organisms evolve to fill
  diverse ecological niches. (In the broadest
  sense, all current species are the result of
  divergent evolution.)