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In historical context. Other people’s ideas paved the path for Darwin’s thinking. competition: struggle for survival population growth exceeds food supply. land masses change over immeasurable time. The History Behind THE Theory. Aristotle

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in historical context
In historical context
  • Other people’s ideas paved the path for Darwin’s thinking


struggle for survivalpopulation growth exceeds food supply

land masses change over immeasurable time

the history behind the theory
The History Behind THE Theory
  • Aristotle
    • viewed species as fixed and arranged them on a scala naturae of increasing complexity
  • Linnaeus
    • interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose
    • founder of taxonomy, the branch of biology concerned with classifying organisms by the use of binominal nomenclature (genus and species)

The History Behind THE Theory


Determined some past organisms differ greatly from living species by looking at fossils in various strata

Some organisms became extinct


Published his idea of gradualism: the Earth had been molded by several events over time


The History Behind THE Theory

  • Lyell
  • Lamarck
    • Simple life forms develop into more complex forms through use and disuse
    • Individuals can acquire traits during their lifetime and pass on those traits to their offspring (inheritance of acquired characteristics)
  • Uniformitarianism: Geologic processes that have changed the shape of the Earth’s surface in the past continue to work in the same ways.
the history behind the theory1
The History Behind THE Theory
  • Wallace
    • Published the first essay discussing the process of natural selection that was identical to Darwin’s that had yet to be published

The History Behind THE Theory

  • Charles Darwin
    • 1809-1882
    • British naturalist
    • Proposed the idea of evolution by natural selection
    • Collected clear evidence to support his ideas
voyage of the hms beagle
Voyage of the HMS Beagle
  • Invited to travel around the world
    • 1831-1836 (22 years old!)
    • makes many observations of nature
      • main mission of the Beagle was to chart South American coastline

Robert Fitzroy

voyage of the hms beagle1
Voyage of the HMS Beagle
  • Stopped in Galapagos Islands
    • 500 miles off coast of Ecuador
succession of types

Glyptodont fossils are also unique to South America.

Succession of types

Armadillos are native to the Americas, with most species found in South America.

Why should extinct armadillo-like species& living armadillos be found on the samecontinent?


Modern sloth (right)

Mylodon (left) Giant ground sloth (extinct)

“This wonderful relationship in the same continent between the dead and the living will…throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other class of facts.”

darwin found birds
Darwin found… birds

Collected many different birds on the Galapagos Islands.

Thought he found very different kinds…





but darwin found a lot of finches
But Darwin found… a lot of finches

Darwin was amazed to find out:

All 14 species of birds were finches…

But there is only one species of finch on the mainland!

Large Ground Finch

Small Ground Finch



How didone species of finches becomeso many differentspecies now?

Warbler Finch

Veg. Tree Finch



darwin s theory of natural selection
Darwin’s Theory of Natural Selection
  • He described evolution with the phrase “descent with modification” meaning that all species descended from preexisting species but changed over time.
essence of darwin s ideas
Essence of Darwin’s ideas
  • Natural selection
    • variation exists in populations
    • over-production of offspring
      • more offspring than the environment can support
    • competition
      • for food, mates, nesting sites, escape predators
    • differential survival
      • successful traits = adaptations
    • differential reproduction
      • adaptations become more common in population
lamarckian vs darwinian view

LaMarckian vs. Darwinian view
  • LaMarck
    • in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring
  • Darwin
    • giraffes born with longer necks survive better & leave more offspring who inherit their long necks
tree thinking
Tree Thinking



Large-seed eater?

Large GroundFinch

Small-seed eater?

Small GroundFinch



Veg. Tree Finch

Warbler Finch

correlation of species to food source
Correlation of species to food source




Rapid speciation:new species filling new niches,because they inheritedsuccessful adaptations.

Adaptive radiation

darwin s finches
Darwin’s finches
  • Differences in beaks
    • associated with eating different foods
    • survival & reproduction of beneficial adaptations to foods available on islands

Warbler finch

Cactus finch

Woodpecker finch

Sharp-beaked finch

Small insectivorous

tree finch

Small ground






tree finch



Mediumground finch

Tree finches

Ground finches

Insect eaters

Seed eaters


tree finch

Large ground finch

Bud eater

darwin s finches1
Darwin’s finches
  • Darwin’s conclusions
    • small populations of original South American finches landed on islands
      • variation in beaks enabled individuals to gather food successfully in the different environments
    • over many generations, the populations of finches changed anatomically & behaviorally
      • accumulation of advantageous traits in population
      • emergence of different species
darwin s finches2
Darwin’s finches
  • Differences in beaks allowed some finches to…
    • successfully compete
    • successfully feed
    • successfully reproduce
      • pass successful traits onto their offspring
correlation of species to food source1
Correlation of species to food source

More observations…

Whoa,Turtles, too!


Many islands also show distinct local variations in tortoise morphology…

…perhaps these are the first steps in the splitting of one speciesinto several?