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Chapter 7 Evolution and the Fossil Record Chapter 7 - Guiding Questions What lines of evidence convinced Charles Darwin that organic evolution produced the species of the modern world? What are the components of natural selection?

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chapter 7

Chapter 7

Evolution and the Fossil Record

chapter 7 guiding questions
Chapter 7 - Guiding Questions
  • What lines of evidence convinced Charles Darwin that organic evolution produced the species of the modern world?
  • What are the components of natural selection?
  • What is the source of the variability that is the basis of natural selection?
  • What role does geography play in speciation?
  • What factors lead to evolutionary radiation?
  • Why is convergence one of the most convincing kinds of evidence that evolutionary changes are adaptive?
  • Why do species become extinct?
  • What is mass extinction?
  • In what ways can evolutionary trends develop?
evolution
Evolution

Evolution

  • changes in populations, which consist of groups of individuals that live together and belong to the same species
  • a change in gene frequencies
  • populations evolve, not individuals
    • YOU can’t evolve!

Extinct ground sloth (20 ft long)

evolution4
Evolution

Adaptations

  • specialized features of animals and plants (or any other organism) which perform one or more useful functions
  • allow that organism to excel in its environment
  • YOU can only modify characteristics over which your genes have control; e.g., tanning

Cat skull

Horse skull

Venus Flytrap

inefficient evolution
Inefficient Evolution
  • can only operate by changing what is already present;
  • it’s the business of remodeling rather than new construction from scratch
  • e.g., to make a new structure, natural selection starts by modifying an already existing one
    • e.g., how could ‘night vision’ evolve?
charles darwin
Charles Darwin
  • 1831
    • set sail on the Beagle
    • schooled in uniformitarianism
      • Lyell’s Principles of Geology
    • a keen observer of natural phenomena
  • 1859-On the Origin of Species by Natural Selection
some of darwin s observations
Some of Darwin’s Observations
  • Rhea
    • large flightless birds
    • found only in South America
    • also found extinct, fossil forms
  • Some similarities but also obvious differences from ostrich (Africa) and emu (Australia)
more of darwin s observations
More of Darwin’s Observations
  • sloths and extinct armadillos
    • unique to the Americas
more of darwin s observations9
More of Darwin’s Observations
  • Oceanic islands
    • many barren; Hawaii has no native snakes, frogs, FW fish, etc.
    • species must have originated elsewhere
  • Galápagos Islands
    • tortoises with shells unique on each island
    • shared a common ancestry
    • followed later by differentiation
galapagos islands
Galapagos Islands

Range from 3 to 5 my old

galapagos tortoises
Galapagos Tortoises
  • 14 subspecies, 11 extant, several with very small populations
    • e.g., Lonesome George
lonesome george
Lonesome George

Isla Pinta

darwin s famous finches

Finches of the Galápagos

    • different beak types
      • slender-insectivorous
      • sturdy-seed crushing
      • woodpecker-like-tool user
    • differentiation based on lifestyle
    • curiously resemble a South American mainland finch
Darwin’s Famous Finches
charles darwin16
Charles Darwin
  • Additional observations
    • Anatomical relationships
      • embryos of many vertebrates are quite similar, even superficially indistinguishable
charles darwin18
Charles Darwin
  • Additional observations
    • Anatomical relationships
      • embryos of many vertebrates quite similar
      • homology
        • presence in two different groups of animals or plants of organs that have the same ancestral origin but serve different functions
charles darwin20
Charles Darwin
  • Additional observations
    • Anatomical relationships
      • embryos of many vertebrates quite similar
      • homology
        • presence in two different groups of animals or plants of organs that have the same ancestral origin but serve different functions
      • vestigial organs
        • organs that serve no apparent purpose but resemble organs that perform functions in other creatures
theory of evolution
Theory of Evolution
  • Natural Selection- ‘survival of the fittest’
    • the process that operates in nature but parallels the artificial selection by which breeders develop new varieties of plants and animals
      • success of an individual determined by advantages it has over others
        • survives to bear offspring with same trait
the basis for natural selection
The Basis for Natural Selection
  • There is much variation between members of a species.
the basis for natural selection29
The Basis for Natural Selection
  • There is much variation between members of a species
  • Reproduction is way in excess of the number that the habitat can survive

e.g., Robins

the basis for natural selection31
The Basis for Natural Selection
  • There is much variation between members of a species
  • Reproduction is way in excess of the number that the habitat can survive

e.g., Robins

3. Differential reproductive success-those best adapted survive to reproduce the most

theory of evolution33
Theory of Evolution
  • Darwin didn’t have all the tools we have today to explain his idea.
  • Genetics was in its infancy—Mendel’s ideas, though contemporary with Darin, weren’t appreciated for decades.
  • Genes-hereditary factors
  • Particulate inheritance
    • Gregor Mendel’s idea that organisms retain identities through generations
    • Peas
      • No blending
      • Colors could be masked for generations
theory of evolution35
Theory of Evolution
  • Mutations
    • alteration of genes
    • provides for variability
    • very few are helpful
  • DNA
    • Deoxyribonucleic Acid
    • transmits chemically coded information
    • mostly found in chromosomes
theory of evolution37
Theory of Evolution
  • sexual recombination
    • each parent contributes one half of its chromosomes to offspring via a gamete
      • special reproductive cell containing one of each type of chromosome
        • female ovum/egg; male sperm
    • yields new combinations-e.g., my kids aren’t exact copies of me; genes of their mother and me are both present.
      • mutations increase variability—and we all have them!
  • gene pool
    • sum total of genetic components of a population or group of interbreeding individuals
    • you have only a small subset of the human gene pool
      • reproductive barriers limit the pool and keep species separate
  • speciation
    • origin of a new species from two or more individuals of a preexisting species
reproductive isolation
Reproductive Isolation

Fall breeder

Spring breeder

origination
Origination
  • Evolutionary radiations
    • pattern of expansion from some ancestral adaptive condition represented by descendant taxa
  • adaptive breakthrough
    • appearance of key features that allow radiation to occur
  • fossil record documents patterns
    • E.g., Jurassic corals
origination41
Origination
  • Rates of speciation
    • Galápagos Islands-formed millions of years ago
    • Lake Victoria
      • 13,000 years old
      • 497 unique species of cichlid fish, many with specialized adaptations
  • Molecular clock
    • assume average rate of mutation
    • determine pace of change
    • extrapolate timing of change
convergence
Convergence
  • Evolution of similar forms in two or more different biological groups
  • Marsupials and placental mammals
    • similar form
    • isolated, adaptive convergent evolution after initial divergence
extinction
Extinction
  • caused by extreme impacts of limiting factors
    • predation
    • disease
    • competition
  • pseudoextinction
    • species evolutionary line of descent continues but members are given a new name
  • high rates of extinction make useful index fossil
    • ammonoids
extinction44
Extinction
  • rates
    • average rate has declined through time
  • mass extinctions
    • many extinctions within a brief interval of time
    • largest events peak at extinction of >40% genera
    • rapid increase (radiation) follows
modern mass extinctions
Modern Mass Extinctions
  • fossil patterns reflected in modern
    • tropical species
    • large animals
  • loss of habitat
  • direct exploitation
  • likely replacement by opportunistic species
evolutionary trends
Evolutionary Trends
  • Cope’s rule
    • body size increases during evolution of a group of animals
    • structural limitations on size
  • specialized adaptations limit evolution
    • elephants
    • manatees
evolutionary trends47
Evolutionary Trends

Whales

  • terrestrial origin
    • 50 Ma
    • small (2 m) mammals with feet
  • marine adaptation
    • 40 Ma
    • lost hind limbs
    • no pelvic bones
    • up to 20 m
phylogeny
Phylogeny
  • Phylogeny
    • complex, large-scale trend within a branching tree of life
    • gradual large-scale change from one species to another is rare
      • e.g., Jurassic coiled oysters
phylogeny49
Phylogeny
  • Axolotl
    • example of rapid speciation from parent species
      • parent is amphibious
      • offspring is aquatic throughout life after one simple genetic change
phylogeny50
Phylogeny
  • rates
  • gradualistic model
    • very slow rates
  • punctuational model
    • rapid evolution with little change between steps
    • bowfin fish
      • little change in 60 m.y.
phylogeny51
Phylogeny
  • Horses
    • increase in body size
    • evolved tall complex molars and single-hoofed toe
    • change driven by climate
      • expansion of grasslands
  • Dollo’s law
    • evolutionary transition from at least several genetic changes is highly unlikely to be reversed by subsequent evolution
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