Evolution and Darwin

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EvolutionandDarwin
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Evolution

• The processes that have transformed life on earth
  from its earliest forms to the vast diversity
  that characterizes it today.
• A change in the genes!!!!!!!!

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Old Theories of Evolution

• Jean Baptiste Lamarck (early 1800s) proposed
• The inheritance of acquired characteristics
• He proposed that by using or not using its body
  parts, an individual tends to develop certain
  characteristics, which it passes on to its
  offspring.

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The Inheritance of Acquired Characteristics

• Example
• A giraffe acquired its long neck because its
  ancestor stretched higher and higher into the
  trees to reach leaves, and that the animals
  increasingly lengthened neck was passed on to its
  offspring.

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Charles Darwin

• Influenced by Charles Lyell who published
  Principles of Geology.
• This publication led Darwin to realize that
  natural forces gradually change Earths surface
  and that the forces of the past are still
  operating in modern times.

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Charles Darwin

• Darwin set sail on the H.M.S. Beagle (1831-1836)
  to survey the south seas (mainly South America
  and the Galapagos Islands) to collect plants and
  animals.
• On the Galapagos Islands, Darwin observed species
  that lived no where else in the world.
• Patterns of diversity, e.g., Pinta, Isabela and
  Hood island tortoises that ate vegetation, birds
  (finches) on Galapagos islands
• Far more species than previously known
• Similar ecosystems did not have same species
• Species adapted to their habitat
• Fossils preserved remains of ancient organism
• These observations led Darwin to write a book.

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Charles Darwin

• Wrote in 1859 On the Origin of Species by Means
  of Natural Selection
• Two main points
• 1. Species were not created in their present
  form, but evolved from ancestral species.
• 2. Proposed a mechanism for evolution
  NATURAL SELECTION

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Natural Selection

• Individuals with favorable traits are more likely
  to leave more offspring better suited for their
  environment.
• Also known as Differential Reproduction
• Example
• English peppered moth (Biston betularia)
• - light and dark phases

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Peppered moths rest on trees and depend on
camouflage for protection.
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Evolution by Natural Selection

• Evolution by Natural Selection
• Struggle for existence competition for
  resources
• Survival of the fittest (natural selection)
  Fitness is a result of adaptations
• Adaptation any inherited characteristic that
  increases an organisms chance of survival
• Types of adaptation-
• Camouflage
• Mimicry one species resembles another
• Antimicrobial resistance

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Darwins Beliefs About Descent

• Descent with modification over long periods of
  time, natural selection produces organisms that
  have different structures, niches or occupy
  different habitats. Each species has descended
  with changes from other species over time.
• Common descent all living and extinct species
  were derived from common ancestors

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Artificial Selection

• Artificial selection nature provides the
  variation, but humans select the variations they
  find useful, e.g. breeding the largest hogs,
  fastest horses
• The selective breeding of domesticated plants and
  animals by man.
• Question
• Whats the ancestor of the domesticated dog?
• Answer WOLF

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Evidence of Evolution

• 1. Biogeography
• Geographical distribution of species.
• Convergent Evolution - similar environments
  leads to unrelated species with similar traits
• 2. Fossil Record
• Fossils and the order in which they appear in
  layers of sedimentary rock (strongest evidence).

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Evidence of Evolution

• 3. Comparative anatomy
• Homologous structures Structures
• that are similar because of
• common ancestry
• Vestigal structures traces of homologous
  organs in other species

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Evidence of Evolution

• 4. Comparative embryology
• Study of structures that appear during
  embryonic development.
• 5. Molecular biology
• DNA and proteins (amino acids)
• 6. Experimental evidence

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Population Genetics

• The science of genetic change in population.

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Population

• A localized group of individuals belonging to the
  same species.

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Species

• A group of populations whose individuals have the
  potential to interbreed and produce viable
  offspring.

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Gene Pool

• The total collection of genes in a population at
  any one time.

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Genetics and Evolution

• Relative frequency number of times an allele is
  present in a gene pool, compared to the number of
  times other alleles for the same gene are present
  o EX Black (B) fur 40 and b fur 60 in mice o
  In genetic terms, evolution is the change in
  relative frequency of alleles in a population o
  May not match Mendelian ratios
• Sources of genetic variation o Mutations
  change in sequence of DNA o Gene shuffling
  different combinations of genes during gamete
  production and crossing over
• Single gene and polygenic traits o Natural
  selection on single gene traits can lead to
  changes in allele frequencies and thus evolution
  (Ex lizard color, red easy to see and black
  keeps lizard warmer, reduction in normal brown
  which has no advantage) o Polygenic Natural
  selection is more complex and can affect
  distributions of phenotypes in 3 modes of action

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Modes of Action

• Natural selection has three modes of action
• 1. Stabilizing selection
• 2. Directional selection
• 3. Diversifying selection

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1. Stabilizing Selection

• Acts upon extremes and favors the intermediate.

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2. Directional Selection

• Favors variants of one extreme.

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3. Diversifying Selection

• Favors variants of opposite extremes.

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Hardy-Weinberg Principle

• The concept that the shuffling of genes that
  occur during sexual reproduction, by itself,
  cannot change the overall genetic makeup of a
  population.

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Hardy-Weinberg Principle

• This principle will be maintained in nature only
  if all five of the following conditions are met
• 1. Very large population
• 2. Isolation from other populations
• 3. No net mutations
• 4. Random mating
• 5. No natural selection

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Hardy-Weinberg Principle

• Remember
• If these conditions are met, the population
  is at equilibrium.
• This means No Change or No Evolution.

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Macroevolution

• The origin of taxonomic groups higher than the
  species level.

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Microevolution

• A change in a populations gene pool over a
  secession of generations.
• Evolutionary changes in species over relatively
  brief periods of geological time.

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Five Mechanisms of Microevolution

• 1. Genetic drift
• Change in the gene pool of a small population
  due to chance.
• Two examples
• a. Bottleneck effect
• b. Founder effect

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a. Bottleneck Effect

• Genetic drift (reduction of alleles in a
  population) resulting from a disaster that
  drastically reduces population size.
• Examples
• 1. Earthquakes
• 2. Volcanos

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b. Founder Effect

• Genetic drift resulting from the colonization of
  a new location by a small number of individuals.
• Results in random change of the gene pool.
• Example
• 1. Islands (first Darwin finch)

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Five Mechanisms of Microevolution

• 2. Gene Flow
• The gain or loss of alleles from a population
  by the movement of individuals or gametes.
• Immigration or emigration.

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Five Mechanisms of Microevolution

• 3. Mutation
• Change in an organisms DNA that creates a new
  allele.
• 4. Non-random mating
• The selection of mates other than by chance.
• 5. Natural selection
• Differential reproduction.

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Speciation

• The evolution of new species.

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Reproductive Barriers

• Any (isolation) mechanism that impedes two
  species from producing fertile and/or viable
  hybrid offspring.
• Two barriers
• 1. Pre-zygotic barriers
• 2. Post-zygotic barriers

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1. Pre-zygotic Barriers

• a. Temporal isolation
• Breeding occurs at different times for
  different species.
• b. Habitat isolation
• Species breed in different habitats.
• c. Behavioral isolation
• Little or no sexual attraction between
  species.

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1. Pre-zygotic Barriers

• d. Mechanical isolation
• Structural differences prevent gamete
  exchange.
• e. Gametic isolation
• Gametes die before uniting with gametes of
  other species, or gametes fail to unite.

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2. Post-zygotic Barriers

• a. Hybrid inviability
• Hybrid zygotes fail to develop or fail to
  reach sexual maturity.
• b. Hybrid sterility
• Hybrid fails to produce functional gametes.
• c. Hybrid breakdown
• Offspring of hybrids are weak or infertile.

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Allopatric Speciation

• Induced when the ancestral population becomes
  separated by a geographical barrier.
• Example
• Grand Canyon and ground squirrels

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Adaptive Radiation

• Emergence of numerous species from a common
  ancestor introduced to new and diverse
  environments.
• Example
• Darwins Finches

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Sympatric Speciation

• Result of a radical change in the genome that
  produces a reproductively isolated sub-population
  within the parent population (rare).
• Example Plant evolution - polyploid
• A species doubles its chromosome to become
  tetraploid.

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Interpretations of Speciation

• Two theories
• 1. Gradualist Model (Neo-Darwinian)
• Slow changes in species overtime.
• 2. Punctuated Equilibrium
• Evolution occurs in spurts of relatively
  rapid change.

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Convergent Evolution

• Species from different evolutionary branches may
  come to resemble one another if they live in very
  similar environments.
• Example
• 1. Ostrich (Africa) and Emu (Australia).
• 2. Sidewinder (Mojave Desert) and
• Horned Viper (Middle East Desert)

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Coevolution

• Evolutionary change, in which one species act as
  a selective force on a second species, inducing
  adaptations that in turn act as selective force
  on the first species.
• Example
• 1. Acacia ants and acacia trees
• 2. Humming birds and plants with flowers with
  long tubes

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Fossils

• Fossil - traces and preserved remains of ancient
  life, formed in sedimentary rock
• Types of fossils
• Trace - indirect evidence, e.g., footprints
• Mold impression b of an organism
• Cast mold filled with sediment
• Replacement original organism replaced with
  mineral crystals
• Petrified empty pore spaces filled with
  minerals, e,g petrified wood
• Amber preserved tree sap traps organism
• Original material mummified or frozen

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How Are Fossils Dated?

• Relative dating age of a fossil is determined
  by comparing placement with that of fossils in
  other layers of rock
• Index species compared with other fossils
  because they are easily recognized, lived for a
  short time and had wide geographic range
• Radioactive dating use radioactive decay to
  assign absolute ages to rocks
• Half life length of time required for half of
  the radioactive atoms in a sample to decay

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Early history of life

• Solar system 12 billion years ago (bya)
• Earth 4.5 bya
• Life 3.5 to 4.0 bya
• Prokaryotes 3.5 to 2.0 bya stromatolites
• Oxygen accumulation 2.7 bya photosynthetic
  cyanobacteria
• Eukaryotic life 2.1 bya
• Muticelluar eukaryotes 1.2 bya
• Animal diversity 543 mya
• Land colonization 500 mya

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The Origin of Life

• Old theory of origin of life spontaneous
  generation (from non-living) Theory of
  biogenesis (life from life) Redi, Pasteur
  Early Atmosphere - hydrogen cyanide, carbon
  dioxide, carbon monoxide, nitrogen, hydrogen
  sulfide and water

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Early Life

• How did first cells (bacteria) form?
• Protenoid microspheres large organic molecules
  form tiny bubbles
• First life anaerobic, living in the oceans
• Microfossils (microscopic) 3.5 billion years old,
  when little oxygen in atmosphere
• By 2.2 billion years, fossil evidence of
  microfossils that were photosynthetic

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Organic monomers/polymer synthesis

• Miller/Urey experiment
• Water, hydrogen, methane, ammonia
• No oxygen
• All 20 amino acids, nitrogen bases, ATP formed

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The Endosymbionic Theory

• Mitochondria and chloroplasts were formerly from
  small prokaryotes living within larger cells
  (Margulis)

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Evidence of The Endosymbionic Theory

• Mitochondria and chloroplasts
• DNA is similar to prokaryotic DNA
• Have their own ribosomes
• Can undergo binary fission