Chapters 22-25 Evolution

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Chapters 22-25Evolution
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Evolution

• The definition of Evolution is
• change over time
• Biological Evolution is
• genetic change in population over time
• process by which modern organisms have descended
  from ancient organisms (slow change over long
  time)
• Even relatively quick evolution takes hundreds of
  thousands of years

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History of Evolutionary Theories

• Plato (427-347 B.C.) 2 worlds 1 perfect, 1
  imperfect. No change in organisms
• Aristotle (384-322 B.C.) Organisms placed on
  ladder of complexity / perfection (scala
  naturae) No change
• Judeo-Christian culture tried to explain the
  Creators plan as observable, natural phenomena
  Natural Theology

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History of Evolutionary Theories

• Carolus Linnaeus (1707-1832) Designed modern
  taxonomic system (binomial nomenclature)
• From this system, we can (he didnt) now infer
  evolutionary relationships between different
  groups
• Geologists
• Georges Cuvier
• James Hutton
• Charles Lyell

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History of Evolutionary Theories

• Georges Cuvier (1769-1832) helped develop
  Paleontology study of fossils
• Discovery of fossils (extinct species,
  similarities to modern species) put some doubt
  into Earths age and the origin of species
• Cuvier explained differences in strata with
  catastrophism floods, droughts, volcanoes,
  etc. changed local areas drastically over short
  periods of time
• Organisms did not change, just migrate

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History of Evolutionary Theories

• James Hutton (1726-1797) proposed that rocks,
  mountains, and valleys have been changed by
  water, wind, temperature, volcanoes, and other
  natural forces
• He described the slow processes that shape Earth
  as gradualism

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History of Evolutionary Theories

• Charles Lyell (1797-1875) agreed with Hutton
  and said that scientists must always explain past
  events in terms of observable, PRESENT events and
  processes (uniformitarianism what happens
  today happened yesterday)
• They theorized Earth was much older than a
  few thousand (6,000) years, which didnt
  set well in the traditional
  timeframe of Creationism

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Age of the Earth

• We now know Earth is approximately 4.5 billion
  years old
• Darwin used the work of Hutton and Lyell as a
  basis for his theories of slow change over time.
  Darwins work was a biological duplicate of
  Hutton and Lyells works in geology.

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Geologists study Earths rocks

• Fossils are preserved remains of ancient
  organisms
• As fossils are found that dont resemble
  organisms today, evidence increases that Earth
  has changed and that organisms have changed with
  it
• Biologists and geologists date Earths past with
  the help of rocks

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Geological Time Scale

• RELATIVE DATING
• Technique used to determine age of fossils
  relative to other fossils in different strata
• This technique is VERY approximate

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Geological Time Scale

• ABSOLUTE (RADIOMETRIC) DATING
• Using radioactive elements in rock that decay at
  a steady rate to determine age
• Decay measured in terms of HALF-LIFE
• Half-life time required for half the
  radioactive atoms in a sample to decay

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Radioactive Decay

• During radioactive decay, the atoms of one
  element break down to form something else

Lose a proton
6 protons 4 neutrons
5 protons 4 neutrons
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• Rocks contain radioactive elements, each having a
  different half-life
• EXAMPLES
• Uranium-238 ? Lead-206 HL 4.5 B yrs
• Potassium-40 ? Argon-40 HL 1.3 B yrs
• Carbon-14 ? Nitrogen-14 HL 5770 yrs

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• Scientists often date rocks using Potassium-40,
  which decays to form the stable element Argon-40
• It has a half life of 1.3 billion years
• This is used to date the oldest rocks on earth

Formed
1.3 B yrs
2.6 B yrs
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• Uranium and Potassium are useful for dating rocks
• Carbon-14 is useful for dating things that were
  once alive such as wood, natural fiber, or cloth
• C-14 is in the atmosphere living things take it
  in their cells. After the organism dies, it
  doesnt take in any more C-14. We can then
  compare the amounts of C-14 to N-14, knowing its
  half-life, to determine the age of the sample

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Fossil Evidence

• Found in Sedimentary rock layers of sand,
  silt, and clay in streams, lakes, rivers, and
  seas form rock that may have trapped living
  organisms
• Fossil records Show change over time. Some
  time frames are missing, but will show change of
  climate and geography.
• Ex Shark teeth in Utah
• How can this be?

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Jean Baptiste de Lamarck (1744-1829)

• He also recognized that organisms were adapted to
  their environments and that they change
• He relied on three ideas
• A desire to change (innate drive for perfection)
• Use and disuse (Giraffes necks and vestigial
  organs)
• Inheritance of acquired characteristics

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Darwins Dilemma

• Set sail around the world in 1831 on HMS Beagle
  on a 5 year voyage
• He had prior knowledge of geology (Lyell was a
  good friend) and agriculture that helped
  influence the development of his theory
• Anchored all along the way and took samples
  from each place

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Darwins Dilemma

• He collected and studied beetles from Brazil,
  birds from Chile, and iguanas, tortoises, and
  finches from the Galápagos Islands
• He noticed similarities between mainland
  (Ecuador) and Galapagos finches
• Later, he noticed differences in beak size among
  finches from different islands in the Galapagos

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Darwins Dilemma

• Thomas Malthus wrote paper on population growth
  in Great Britain
• Population grows exponentially
• Limiting factors on growth (carrying capacity)
• Food
• Area
• Resources

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Darwins Dilemma

• Darwin applied Malthus, Huttons, and Lyells
  work to species ability to change, and called
  the mechanism Natural Selection
• Nat.Sel. Process by which organisms with
  favorable variations survive and produce more
  offspring than less well-adapted organisms
• He was sure Nat.Sel. was true, but he
  feared public ridicule. So, he kept his
  ideas to himself

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Darwins Dilemma

• Alfred Russel Wallace (1823-1913), working
  independently, came to the same conclusions as
  Darwin
• He sent a manuscript to Darwin, basically for
  proofreading
• I never saw a more striking coincidence so all
  my originality, whatever it may amount to, will
  be smashed. Charles Darwin
• Letter to Charles Lyell, June 18, 1858
• Darwin quickly abridged and published his work
  On the Origin of Species

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Darwins Natural Selection

• Ernst Mayr, an evolutionary biologist, has
  dissected the logic of Darwins theory into three
  inferences based on five observations (Pg. 435)
• Observations
• Tremendous fecundity
• Stable populations sizes
• Limited environmental resources
• Variation among individuals
• Heritability of some of this variation.

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Darwins Natural Selection

• Observation 1 All species have such great
  potential fertility that their population size
  would increase exponentially if all individuals
  that are born reproduced successfully.

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Darwins Natural Selection

• Observation 2 Populations tend to remain stable
  in size,except for seasonal fluctuations.
• Observation 3 Environmental resources are
  limited.

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Darwins Natural Selection

• Inference 1 Production of more individuals than
  the environment can support leads to a struggle
  for existence among the individuals of a
  population, with only a fraction of the offspring
  surviving each generation.

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Darwins Natural Selection

• Observation 4 Individuals of a population vary
  extensively in their characteristics no two
  individuals are exactly alike.
• Observation 5 Much of this variation is
  heritable.

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Darwins Natural Selection

• Inference 2 Survival in the struggle for
  existence is not random, but depends in part on
  the hereditary constitution of the individuals.
• Those individuals whose inherited characteristics
  best fit them to their environment are likely to
  leave more offspring than less fit individuals.

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Darwins Natural Selection

• Inference 3 This unequal ability of
  individuals to survive and reproduce will lead to
  a gradual change in a population, with favorable
  characteristics accumulating over the generations.

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Evidence in Living Organisms

• Comparative embryology
• All vertebrate embryos look similar to one
  another in early development, with the
  development of a tail and gill arches
• Ernst Haeckel made early drawings later exposed
  as frauds.
• Gave fuel to anti-evolutionists

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Evidence in Living Organisms

• Comparative embryology
• These anatomical similarities indicate similar
  genetics are at work
• Become more dissimilar as they grow
• Cell specialization and differentiation
• Common ancestor?

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Evidence in Living Organisms
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Evidence in Living Organisms

• Comparative anatomy
• Homologous Structures
• Analogous Structures
• Vestigial Organs

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Evidence in Living Organisms

• Homologous Structures structures that are
  similar in anatomy, but may serve very different
  functions
• Ex cat, whale, and human forearm

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Homologous Structures
Flying
Swimming
Running
Grasping
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Evidence in Living Organisms

• Analogous Structures structures that serve
  similar functions, but have evolved independently
  of each other

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Not homologousanalogous
Not homologousnot analogous
Homologousnot analogous
Homologous analogous
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Evidence in Living Organisms.

• Vestigial organs organs that have little or no
  purpose in the organism may become smaller or
  even disappear
• Ex Tailbone or appendix in humans
• Ex Tiny leg bones in snakes (boas and
  pythons) thought to come from 4
  legged ancestor

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Evidence in Living Organisms

• Comparative biochemistry and molecular biology
• All cells have DNA, RNA, ribosomes, the same 20
  amino acids and use ATP to do work
• Similarities in biochemistry indicate relationship

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Evidence in Living Organisms

• Cytochrome c is a highly conserved respiratory
  protein containing 104 amino acids in humans

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Evidence in Living Organisms

• Amino acid differences of hemoglobin between
  species

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What Homologies tell us

• Similarities in structure and chemistry provide
  powerful evidence that all living things evolved
  from a common ancestor
• Darwin Concluded
• Living organisms evolved through gradual
  modifications of earlier forms ? descent with
  modification

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What Similarities tell us

• Two types of evolution can account for homologous
  AND analogous structures
• Convergent evolution
• Divergent evolution

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What Similarities tell us

• Divergent evolution two species evolve from a
  common ancestor (speciation)
• They share similarities in anatomy, biochemistry,
  and embryology due to common ancestry
• Explains homologous structures

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What Similarities tell us

• Convergent two species apparently becoming more
  similar
• Two species have adapted in similar ways to
  similar environmental conditions
• NOT due to common ancestry
• Explains analogous structures

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Convergent Evolution

• Ocotillo from California and allauidi from
  Madagascar have evolved similar mechanisms for
  protecting themselves

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Convergent Evolution

• Adaptive radiation of anoles has occurred on the
  islands of the Greater Antilles in a convergent
  fashion. On each island, different species of
  the lizards have adapted to living in different
  parts of trees, in strikingly similar ways.

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Convergent Evolution
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Convergent Evolution
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Diversity of Life

• Fitness
• Physical traits and behaviors that enable
  organisms to survive and reproduce in their
  environment arises from adaptation.
• Adaptation allows species to be better suited to
  their environment and therefore can survive and
  reproduce.

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Evolution on Different Scales

• Microevolution generation-to-generation change
  in a populations allele frequencies
• Macroevolution origin of new taxonomic groups
  speciation

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4 Driving Forces behind Evol.

• Mutation
• Any change in the original DNA
• ONLY ultimate source of variation in a population
• Gene Flow
• Movement of genes either into or out of a
  population
• Migration Immigration (add alleles) and
  Emigration (subtract alleles)

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4 Driving Forces behind Evol.

• Genetic Drift
• Change in the allele frequency in a small
  population by chance alone
• Bottleneck Effect
• Founder Effect

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4 Driving Forces behind Evol.

• Genetic Drift
• Bottleneck Effect population undergoes a high
  mortality rate genetic variation decreases
  dramatically
• Ex Cheetahs

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Genetic Drift Bottleneck Effect
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4 Driving Forces behind Evol.

• Genetic Drift
• Founder Effect few individuals leave a large
  population to start their own gene pool is very
  limited
• Ex polydactyly in PA Amish

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Genetic Drift Founder Effect
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Genetic Drift Founder Effect
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4 Driving Forces behind Evol.

• Selection
• Natural differential success in the
  reproduction of different phenotypes resulting
  from the interaction of organisms with their
  environment
• Nature does the selecting

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4 Driving Forces behind Evol.

• Selection (Natural)
• Resistance overuse of insecticides and
  antibiotics have bred resistant species of bugs
  and germs

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4 Driving Forces behind Evol.

• Selection
• Artificial breeding of domesticated plants and
  animals
• Humans intentionally do the selecting
• Cabbage, cauliflower, Brussels sprouts,
  kale, kohlrabi and broccoli have a
  common ancestor in one species of wild
  mustard

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4 Driving Forces behind Evol.

• Problems with artificial selection not enough
  genetic variation

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4 Driving Forces behind Evol.

• Selection (Sexual)
• Intrasexual selection selection within the same
  sex (competition, usually between males
• Competition, usually between males
• Exaggerated anatomy

Bighorn Sheep
Rocky Mountain Elk
Five-horned Rhinoceros Beetles
Stagbeetles
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4 Driving Forces behind Evol.

• Selection (Sexual)
• Intersexual selection one sex selects mate
  based on phenotypes
• Exaggerated anatomy

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• Selection can influence populations in three
  major ways
• Directional Sel.
• Stabilizing Sel.
• Disruptive (diversifying) Sel.

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Directional Selection

• Environment selects against one phenotypic
  extreme, allowing the other to become more
  prevalent

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Disruptive Selection

• Environment selects against intermediate
  phenotype, allowing both extremes to become more
  prevalent

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Stabilizing Selection

• Environment selects against two extreme
  phenotypes, allowing the intermediates to become
  more prevalent

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Key Points

1. Natural selection does not cause genetic changes
   in individuals.
2. Natural selection acts on individuals evolution
   occurs in populations.
3. Evolution is a change in the allele frequencies
   of a population, owing to unequal success at
   reproduction among organisms bearing different
   alleles.
4. Evolutionary changes are not good nor
   progressive in any absolute sense.

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Evolutionary Theory

• Foundation on which the rest of the biological
  science is built. Collection of carefully
  reasoned and tested hypotheses about how
  evolutionary change occurs.

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Speciation

• What is a species?
• Biological definition a group of closely related
  organisms (population) that can interbreed to
  produce fertile, viable offspring

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Speciation

• Why cant/dont populations interbreed?
• Prezygotic barriers
• Postzygotic barriers

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Prezygotic Barriers

• Ecological (habitat) isolation pops live in
  different habitats and do not meet
• Parasites generally dont transfer hosts
• Temporal isolation active or fertile at
  different times
• Flowering plants pollinate on different days or
  different times of the day

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Prezygotic Barriers

• Behavioral isolation differences in activities
• Mating calls or actions are different

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Prezygotic Barriers

• Mechanical isolation mating organs do not fit
  or match
• Enough said
• Gametic isolation gametes cannot combine
• Sperm destroyed in different vaginal cavity
• Sperm and egg dont fuse due to different
  membrane proteins

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Postzygotic Barriers

• Hybrid inviability hybrid zygotes fail to
  develop or reach sexual maturity
• Hybrid infertility hybrids fail to produce
  functional gametes

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Summary

• 2 or more mechanisms may occur at once
• Ex Bufo americanus and Bufo fowleri are
  ecologically, temporally, and behaviorally
  isolated
• Bufo americanus breeds in early spring in small,
  shallow puddles or nearby dry creeks
• Bufo fowleri breeds in late spring in large pools
  and streams
• Their mating calls also differ

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Limitations of Biological Species Concept

• How do you classify organisms that
• have the potential to interbreed, but do not do
  so in nature?
• do not reproduce sexually?
• exist only as fossils?
• Alternative species concepts (ecological,
  pluralistic, morphological, genealogical) help
  address limitations

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Modes of Speciation

• Allopatric (Greek, allos other Latin, patria
  homeland)
• Speciation due to geographic separation
• Barrier stops gene flow between populations
• Evolutionary change acts independently on each
  pop to establish reproductive barriers

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• Mitochondrial DNA analysis has shown that certain
  tamarin monkey pops (those separated by wide
  rivers) are diverging toward speciation

• Where the Amazon is very wide, tamarins on one
  side are brown, but on the other side are white.
  Where the Amazon is narrow, tamarins of both
  colors are found on either side

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Allopatric Speciation

• Birds can move freely across the gorge of the
  Grand Canyon squirrels cannot
• Two species arose when their original pop was
  disrupted by the carving of the canyon

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• A. harrisi
• A. leucurus

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Allopatric Speciation

• If not given enough time, speciation will not
  occur
• Also, even if they do
  come back together, they
  need to interbreed to be the same
  species

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Allopatric Speciation

• Figure 24.11
• Adaptive Radiation evolution of
  many diversely-adapted species from a
  common ancestor
• Ex Hawaiian archipelago

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Sympatric Speciation

• Sympatric (Greek, sym together Latin, patria
  homeland)
• Speciation occurs in populations that share a
  habitat
• Results from
• Ecological isolation
• Polyploidy (number of sets of chromosomes
  increases)

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Sympatric Speciation

• Polyploidy (number of sets of chromosomes
  increases)
• A result of accidents in meiosis

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Will Speciation Occur?

• p q 1
• p2 2pq q2 1
• Will speciation occur? You tell me!
• Hardy-Weinberg PPT 1
• Hardy-Weinberg PPT 2

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Evolutionary Time Scales

• Evolution can take a long time or can occur
  relatively quickly
• Gradualism
• Punctuated Equilibrium

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Evolutionary Time Scales

• Gradualism big evolutionary changes are the
  result of many small ones over a long period of
  time

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Evolutionary Time Scales

• Punctuated Equilibrium speciation occurs fairly
  rapidly then remain constant

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Evolutionary Novelties

• Unique and highly specialized organs seem to
  complicated to have been naturally selected
• Ex eyes are really just photoreceptors some are
  more developed, but all do the basic function
  receive light

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Evolutionary Novelties
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Evo-devo

• Evolutionary development
• A field of interdisciplinary research that
  examines how slight genetic divergences can
  become magnified into major morphological
  differences between species

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Evo-devo

• By blocking expression of one gene, researchers
  forced a chickens foot to develop to resemble a
  ducks foot
• Two embryos from the same animal

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Evo-devo

• Left, a normal chicken leg will develop

• Right, a normal duck leg will develop from a
  chicken embryo
• Chicken leg scaled with 4 digits
• Duck leg smooth and webbed
• Duck legs, due to one genetic evolutionary
  difference, help ducks do many things chickens
  cannot, like swim