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E volution Thursday 10/24/13. Charles Darwin influences on his thinking // decent with modification evolution by natural selection overview Evidence of Evolution fossil record biogeography comparative anatomy // embryology molecular biology

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Evolution Thursday 10/24/13

  • Charles Darwin
    • influences on his thinking // decent with modification
  • evolution by natural selection
    • overview
  • Evidence of Evolution
    • fossil record
    • biogeography
    • comparative anatomy // embryology
    • molecular biology
    • studies demonstrating evolution


  • change
  • change in
  • change in
  • Charles Darwin – “father of evolution” proposed a mechanism of change over time…….

Historical Context

  • Prevailing thought prior to Darwin’s time:
  • Darwin was strongly influenced by the writings of geologist Charles Lyell
    • Lyell proposed
    • earth was at
  • Darwin reasoned that:
    • IfEarth is
    • then subtle processes occurring

Historical Context

  • Malthus’“Essay on the Principle of Population”(published 1798)
  • Darwin was strongly influenced by the Malthus’ writings and reasoned that:
    • all though all organism
    • only a limited number

The Voyage of the Beagle

  • In December 1831, Darwin left Great Britain on the HMS Beagle to explore the world…..

Darwin’s voyage on HMS Beagle 1831-1836

see fig 27.1


Darwin was intrigued by:

  • Fossil beds of South America
  • Species composition
  • Plants and animals on
  • Yet, species in similar habitats
  • Similar species

Theory of Evolution by Natural Selection:

Based on observations during his travels and subsequent research/experimentation, Darwin proposed a theory to explain how and why populations change over time:

Wrote manuscript – “Origin of Species” in 1844 – not published until 1858

w/in a decade - widely accept that evolution occurs

Fig 27.3


Descent with Modification

Darwin made two main points in The Origin of Species:

  • Organisms inhabiting Earth today
    • not all individuals
    • individuals best fit
    • population becomes

The result of natural selection is evolutionary adaptation:

(b) A Trinidad tree mantid that mimics dead leaves

(a) A flower mantid in Malaysia

(c) A leaf mantid in Costa Rica



  • Darwin did not invent the idea of evolution; he agreed with many philosophers and naturalists that diversity was produced by evolution
  • But scientists did not know how evolution occurred: prior to Darwin there
  • A predecessor to Darwin,

Adaptations / Evolution:

  • Lamarck’s theory of acquired characteristics
    • individuals passed on
    • better variations

fig 27.2


Adaptations / Evolution:

  • Darwin’s theory
    • parents with
    • frequency of adaptive traits

Descent with modification:

Think about “artificial selection”

  • In Nature -- NATURE DOES

Figure 13.5


Evidence of Evolution

  • Grant’s work & the Darwin’s Finches

Rivers bring sediment to the ocean. Sedimentary rocks containing fossils form on the ocean floor.


Over time, additional strata are added, containing fossils from each time period.



As sea levels change and the seafloor is pushed upward, sedimentary rocks are exposed. Erosion by rivers reveals strata; deeper strata contain older fossils.

Younger stratum with more recent fossils

Older stratum with older fossils


  • preserved
  • often found in

The fossil record

  • the
  • testifies that

present day South American armadillo

extinct - found in fossil record


Fossil Record & Transitional species:

  • examples:
    • fish --> early tetrapod --> modern tetrapod (amphibians)
    • early whales --> modern whales


  • the study of the
  • suggested to Darwin that
  • organisms in
  • organisms on isolated islands





Comparative Anatomy

see fig 27.7

    • the comparison of
    • confirms that
  • Homologous characters
  • Analogous characters

Comparative Embryology

  • Comparative Embryology is the comparison of structures

see fig 27.8

Comparative embryology of vertebrates supports evolutionary theory



Molecular Biology

  • Evolutionary relationships among species
  • more closely related evolutionarily:
  • more distantly related evolutionarily:

relative similarity between CytochromeC structure (protein used in ETC)

fig 27.9


Evidence of Evolution

  • Example of microevolution:
    • Darwin’s finches - medium ground finch

Peter and Rosemary Grant

Researchers at Princeton, began studying the finches in the 70’s

Geospiza fortis –

Medium Ground Finch

darwin s finches
Darwin’s finches

South America

  • Grassquit colonized islands from SA 2.3 mya
  • Darwin observed on Beagle 1831-1836


  • noticed: different bills and diets

Researchers captured, measured, weighed, and banded individuals

Medium Ground Finch

Variation in

  • Variation in

variation in

    • population of

Over 20 months 84% disappeared before breeding


Selective pressure:

  • Typically
  • Number and type of seeds

Tribulus seeds

result evolution of greater beak depth
Result: evolution of greater beak depth
  • mean beak depth of finches hatched in 1976:
  • mean beak depth of finches hatched in 1978:
  • fossils:

heritable character!

Evidence of Evolution

  • Example of microevolution: change w/in a population over generations
  • variation in
    • larger bill -
    • smaller bill -
  • weather conditions
  • selective advantage
  • large-billed birds

fig 22.12

see fig 27.11


Evolution of Pesticide- Resistant Insects

  • variation in population
  • differential survival
  • change in frequency of



Evolution at level of POPULATION not individual!

  • insects had gene or did not have gene
    • w/ gene -
    • w/o gene -
    • change in
  • subsequent generations

Adaptations -- Individuals vs. Population:

  • populations adapt
    • variation in the
    • what is “adaptive”
  • individuals are adapted
    • individuals with

Evolution by Natural Selection: summary

  • historical thinking ripe for Darwin’s theory
  • evolution occurs at the
    • changes in frequency
    • constrained by ancestry
  • variety of evidence supports the theory of evolution
    • one mechanism
      • passing down
      • increase probability
    • KEY aspect of