Exploring the History of Life

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Exploring the History of Life

• The Mechanisms of Evolution
• Chapter 14 -15

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Earths Position in the Universe

• 400 years ago the general public thought that the
  earth was the center of the universe
• Sun revolves around the earth
• The earth does not move

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Galileo and Corpernicus

• Demonstrated scientific evidence that the sun is
  at the center of our solar system and the earth
  moves around the sun

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Galileo and the Church

• Religious leaders felt the heliocentric theory
  (sun at the center) was a direct contradiction to
  the literal interpretation of the Bible
• Galileo found guilty of heresy

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Copernican System (Heliocentral Theory)

• Did not destroy peoples belief in God
• Public now accepts the overwhelming evidence for
  the heliocentric theory

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Charles Darwin 1809-1882
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• Opposition to the Theory of Evolution
• Evolutionary theory, more than any other
  scientific theory, is regularly challenged.
• Much of the objection comes from a mistaken view
  of what a scientific theory represents.

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Evidence of Evolution

• Evolution is all the changes that have occurred
  in living things since life began.
• The earth is 4.5 billion years old, and
  prokaryotes evolved 3.5 billion years ago.
• The eukaryotic cell arose 2.1 billion years ago,
  but there was no multicellularity until 700
  million years ago.

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• Evolution encompasses common descent and
  adaptation to the environment.
• Due to common descent, all living things share
  common characteristics they are made of cells,
  take chemicals and energy from the environment,
  respond to external stimuli, reproduce, and
  evolve.
• Many fields of biology give evidence that
  evolution has occurred.

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• Evolutionary Thinking before Darwin
• Rapid advances in new field of geology (spurred
  by need to find coal and iron to fuel Industrial
  Revolution) set stage for Darwins ideas.

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• Evolutionary Thinking before Darwin
• Notions advanced by other biologists have
  influence
• -On voyage, reads Lyells Principles of Geology
  stressed antiquity of Earths history and its
  continual shaping by natural forces (evolution of
  land forms).

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Jean Baptiste Lamarck

• Inheritance of Acquired Characteristics
• Ex how a giraffes long neck was due to
  ancestors feeding on leaves of tall trees, and
  passing traits to offspring

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• Notions advanced by other biologists have
  influence
• -Lamarcks ideas about inheritance of acquired
  characteristics were wrong, but notion of change
  in organism over time was sound.

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• Charles Darwin and the Theory of Evolution
• Darwins contributionStory of
  Darwins
• voyage of discovery. End to medical studies,
• studies theology, sets sail as naturalist on
• HMS Beagle along coastal South America.
• Rich diversity of tropical life, mainland and
  island species, makes deep impression on young
  Darwin.
• Charles Darwin made two points in his book.
• 1. Descent with modification
• 2. Natural Selection

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HMS Beagle 1831-1836
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Galapagos Islands
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Descent with Modification

• The process in which organisms accumulated
  different modifications (or adaptations) to
  diverse ways of life
• Ex The jack rabbit that blends well in the
  desert with long ears that help cool its body

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Natural Selection

• The process by which individuals with inherited
  characteristics well-suited to the environment
  leave more offspring.
• Main concepts of natural selection
• Overproduction of offspring
• Inherited variation in offspring
• Competition
• Best adapted in a given environment survive and
  reproduce to increase their kind
• They are naturally selected

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Variation of Offspring

• Offspring of the same parents are different from
  each other

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Competition

• Since more individuals are born than can survive
  for an extended period of time, they compete for
  resources
• Food
• Living space
• Mates

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Best adapted to a given environment are selected
to survive

• Brown bears
• Adapted to survive in Oklahoma
• Polar bears
• Adapted to survive in Alaska

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Natural Selection of Flies
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Artificial Selection
Collie
Sheltie
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• -Back in England, Malthus book on limits to
  population growth has strong impact (struggle for
  existence, preservation of good traits, loss of
  bad traits).
• -Wallaces letter outlining basic principles of
  natural selection spurs Darwin into taking his
  ideas public.

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Origin of Species 1859
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The Evidence for Evolution Fossil Formation
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• The Evidence for Evolution
• The age of fossils found in sedimentary rocks
  can be determined using radioactive decay.
• Fossils of simpler organisms are found in older
  rocks, newer rocks contain more complex organisms

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Fossil Evidence

• Fossils are the remains of past life, usually
  consisting of hard parts, such as shells, bones,
  or teeth.
• Most fossils are found embedded in sedimentary
  rock.
• Sedimentation causes rock formation as particles
  accumulate in layers any given stratum (layer)
  is older than the one above it, and younger than
  those below.

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• Geological Time Scale
• As a result of studying strata across the earth,
  scientists have divided earths history into
  eras, periods, and epochs.
• There are two ways to date fossils
• Relative dating provides an approximate age based
  on position of the fossil within rock strata.
• Absolute dating uses radioactive isotopes to
  measure the amount of radiation left in a fossil,
  yielding an actual age.

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• Carbon 14 (14C) is the only radioactive isotope
  in organic matter.
• The amount of radioactivity remaining in a fossil
  can be compared with that of a modern sample to
  determine the age of a fossil.
• Radioactive isotopes decay at a known rate the
  half-life of a radioactive isotope is the length
  of time it takes for half of the radioactive
  isotope to change into another stable element.

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Biogeographical Evidence

• Biogeography is the study of the distribution of
  plants and animals throughout the world.
• The worlds six biogeographical regions have
  their own distinct mix of living things.
• Continental drift refers to the changing
  positions of the continents over time.

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• Two hundred twenty-five million years ago, all
  the present land masses belonged to one continent
  (Pangaea).
• The distribution of plants and animals is
  consistent with continental drift.
• Organisms, such as certain seed plant groups or
  reptiles, are widely distributed throughout the
  world.
• Other groups, such as mammals that arose after
  the continents broke up, have great differences
  in species on different continents.

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Continental drift
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Anatomical Evidence

• Despite dissimilar functions, all vertebrate
  forelimbs contain the same sets of bones this
  strongly suggests common descent.
• Structures that are similar because they are
  inherited from a common ancestor are homologous
  structures.
• Analogous structures are used for the same
  purpose but are not due to a common ancestor.

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Comparative Anatomy
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Homologous Structures similar morphology, even
if function is different, indicates a
closeevolutionary relationship
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Homologous Structures
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Analogous Structures
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Analogous Structures demonstrate organisms are
not related evolutionarily similar function,
different morphology
BAT WING INSECT WINGS BIRD
WING
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• Vestigial structures are anatomical features that
  are fully developed in one group but reduced or
  nonfunctional in other, similar groups.
• Vestigial structures can be explained by common
  descent.
• The homology shared by vertebrates extends to
  their embryological development all vertebrates
  have a dorsal notochord and paired pharyngeal
  pouches at some point.
• Evolution modifies existing structures.

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Significance of developmental similarities
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Comparative Embryology
sea lamprey turtle chicken
cat human
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Biochemical Evidence

• All organisms have certain biochemicals in
  common.
• All use DNA, ATP, and many identical or nearly
  identical enzymes.
• Organisms use the same triplet code and the same
  20 amino acids in proteins.
• This similarity is not necessary, but can be
  explained by common descent.

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Significance of biochemical differences
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• Experimental evidence can demonstrate natural
  selection at work
• Endlers experiments with guppies In
  predator-free environments theres an increase in
  number of male guppies with large and brightly
  colored tails, because they are favored by
  females but when predators are reintroduced the
  number of male guppies with smaller, less
  conspicuous tails increases again because the
  flashier fish are eaten by predators.

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14.4 Process of Evolution

• Individuals do not evolve.
• As evolution occurs, genetic changes occur within
  a population, and these lead to phenotypic
  changes that are commonly seen in that
  population.
• Changes in gene frequencies in populations over
  time constitute microevolution.

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Population Genetics

• A population is all the members of a species
  occupying a particular area at the same time
  members of a population reproduce with each other
  to produce the next generation.
• The various alleles of all the gene loci in all
  the members make up the gene pool for the
  population.

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• Hardy and Weinberg used a binomial expression to
  calculate the genotypic and phenotypic
  frequencies of a population
• p2 2pq q2 1
• This expression is used to determine gene
  frequencies at a given time and to predict gene
  frequencies in the future.
• If reproduction is completely random, the
  Hardy-Weinberg equation predicts the same gene
  pool frequencies generation after generation.

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Using the Hardy-Weinberg equation
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• The Hardy-Weinberg Law
• The Hardy-Weinberg law states that gene
  frequencies will stay the same in a large
  population over time provided
• There are no mutations or mutations are balanced.
• There is no genetic drift changes in allele
  frequencies due to chance alone are
  insignificant.
• There is no gene flow no migration of
  individuals in or out of the population.

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• Mating is random individuals pair by chance and
  not by choice.
• There is no selection no selective force favors
  one genotype over another.
• In real life, these conditions are rarely met,
  and microevolution, as seen by changing gene
  frequencies in Hardy-Weinberg equilibrium, occurs.

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Microevolution
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Five Agents of Evolutionary Change

• 1. Mutations
• Mutations provide new alleles and therefore
  underlie all other mechanisms that produce
  variation.
• Mutations alone are unlikely to cause evolution
  selective agents acting on heritable variation
  cause evolution.
• The adaptive value of a mutation depends on the
  environmental conditions.

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• 2. Genetic Drift
• Genetic drift refers to changes in allele
  frequencies of a gene pool due to chance genetic
  drift has a much larger effect in a small
  population.
• The founder effect occurs when a few individuals
  leave the original population and begin a new
  population.
• A bottleneck effect is seen when much of a
  population is killed due to a natural disaster,
  and only a few remaining individuals are left to
  begin a new population.

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Genetic drift
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Founder effect
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• 3. Gene Flow
• Gene flow is the movement of alleles between
  populations, such as when individuals migrate
  from one population to another.
• Gene flow between two populations keeps their
  gene pools similar and prevents close adaptation
  to a local environment.

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• 4. Nonrandom Mating
• Nonrandom mating occurs when individuals pair up,
  not by chance, but according to genotypes and
  phenotypes.
• Inbreeding is an example of nonrandom mating.
• In a human population, inbreeding increases the
  frequency of recessive abnormalities.

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• 5. Natural Selection
• Natural selection is the process by which
  populations become adapted to their environment.
• Evolution by natural selection requires
• Variation
• Inheritance of the genetic difference
• Differential adaptedness
• Differential reproduction.

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• Three types of natural selection are known
• Stabilizing selection an intermediate phenotype
  is favored.
• Directional selection one extreme phenotype is
  favored.
• Disruptive selection both extreme phenotypes
  are favored over an intermediate phenotype.

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Stabilizing selection
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Directional selection
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Disruptive selection
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Maintenance of Variation

• An example of sickle-cell disease shows how
  genetic variation is sometimes maintained within
  a population.
• Persons with sickle cell disease have
  sickle-shaped blood cells, which can lead to
  hemorrhage and death.
• Persons without a sickle-cell gene are
  susceptible to malaria in parts of Africa.
• But heterozygotes, with one sickle-cell gene and
  one normal gene, have only minor problems with
  blood cells and are resistant to malaria.

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15.1 Speciation

• A species is a group of interbreeding
  subpopulations that share a gene pool and are
  isolated reproductively from other species.
• Reproductive isolation can occur due to premating
  isolating mechanisms, in which reproduction is
  not attempted, or postmating isolating mechanisms
  that do not produce fertile offspring.

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Adaptive Radiation

• The evolution of several species of finches on
  the Galapagos Islands is an example of adaptive
  radiation because each one has a different way of
  life.
• Adaptive radiation occurs when a few individuals
  migrate to a new area, then natural selection
  promotes different feeding habits in different
  ecological habitats.

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Adaptive Radiation
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Land Iquana
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Marine Iquana
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Different Tortoises on Each Island
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The Pace of Speciation

• Two hypotheses concern the pace of speciation
• Phyletic gradualism suggests that change is
  slow and steady within a lineage before and after
  a divergence few transitional links would exist.
• Punctuated equilibrium suggests that a period
  of no change is punctuated by period of rapid
  speciation.

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Phyletic gradualism versus punctuated equilibrium
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These organisms are not new speciesWhy?

• Mule

• Liger

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• Mass Extinctions
• Extinction refers to the death of every member of
  a species.
• During a mass extinction, a large percentage of
  species become extinct within a relatively short
  period of time.
• Mass extinctions occurred at the ends of the
  Ordovician, Devonian, Permean, Triassic, and
  Cretaceous periods.
• The Cretaceous mass extinction that led to the
  demise of dinosaurs was likely caused by an
  meteorite hitting the earth.

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Convergent Evolution

• Natural Selection produces analagous (similar)
  adaptations in different organisms in response to
  similar environments
• African Serval cat south american maned wolf
• These animals have similar ears, legs, acute
  hearing, habitat, and Occupy similar niches

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Ostrich in Africa
Rhea in South America
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Life Has Changed

• Millions of species have been found that are
  different from life today

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Horse Evolution
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Florida Museum of Natural History
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50 Million Years of Change
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Variation and Adaptation

• Variation differences between individual
  members of a population
• Members of a species are very similar, but
  differences can be observed, making each
  individual unique.
• May be caused by mutations

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Mutations

• Changes in DNA base sequences
• Most are either neutral or harmful
• Those that allow the organism to survive better
  in a particular environment are good and are more
  likely to be passed on to future generations.

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Most variations are not caused by mutations

• Sexual reproduction combines genes from different
  parents
• Crossing over during meiosis can produce
  variations

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Adaptation

• An inherited trait that increases the
  populations chances of survival and reproduction
  in a particular environment.
• Allows organisms to fit best into a particular
  niche (habitat and role)

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Biodiversity

• The variety and abundance of species that makes
  up a biological community.
• Pine Barrens forests have little biodiversity a
  limited number of species can survive there.
• Tropical rain forests have great biodiversity
  many species in a concentrated area.

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Divergent Evolution

• Isolated populations of a species evolve
  independently of each other.
• Ex polar bears and brown bears

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Coevolution

• Species that interact closely often adapt to one
  another

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Classification

• Classification involves the assignment of species
  to a hierarchy of categories species, genus,
  family, order, class, phylum, kingdom, and
  domain.
• Each species has a binomial scientific name
  including the genus and species.
• Humans are Homo sapiens.

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Five-Kingdom System

• The five-kingdom system of classification is
  based on structural differences and also on modes
  of nutrition among the eukaryotes.
• The five kingdoms include
• Monera (prokaryotes)
• Eukaryotic kingdoms of Protista, Fungi, Plantae,
  and Animalia.

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Five-kingdom system of classification
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Three-Domain System

• The three-domain system recognizes three domains
  Bacteria, Archaea, and Eukarya.
• This system of classification is based on
  biochemical differences that show there are three
  vastly different groups of organisms.

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Three-domain system of classification
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The three domains of life