Charles Darwin and Alfred Russell Wallace - PowerPoint PPT Presentation

1 / 16
About This Presentation
Title:

Charles Darwin and Alfred Russell Wallace

Description:

... age of 22 he left on a scientific voyage to circle the globe on the HMS Beagle. ... Voyage of the H.M.S. Beagle. The Galapagos Islands ... – PowerPoint PPT presentation

Number of Views:1072
Avg rating:3.0/5.0
Slides: 17
Provided by: virtualYo
Category:

less

Transcript and Presenter's Notes

Title: Charles Darwin and Alfred Russell Wallace


1
Charles Darwin and Alfred Russell Wallace
  • Natural Selection

2
  • Charles Darwin (1809-1882)- Grew up in a wealth
    family.
  • Attended medical school at the University of
    Edinburgh.
  • Being dissatisfied after two years he left for
    Christs College, Cambridge.
  • Natural Science
  • After graduation in 1831 at the age of 22 he left
    on a scientific voyage to circle the globe on the
    HMS Beagle.
  • Believed in fixity of species. However, he began
    to have doubts.
  • Galapagos Islands noted that the flora and fauna
    of South America showed striking similarities to
    those of the Galapagos, as well as intriguing
    differences.

Darwin as a young man
3
Voyage of the H.M.S. Beagle
4
The Galapagos Islands
5
  • He recognized that the various Galapagos finches
    had all descended from a common, mainland
    ancestor and had become modified in response to
    the varying island habitats and to altered
    dietary preferences.
  • However, it was only in retrospect that he
    considered the factors that lead to the
    modification of 1 species into 13.
  • By the late 1830s, Darwin recognized that
    biological variation within species was
    critically important.
  • He acknowledge the importance of sexual
    reproduction in increasing variation.

6
  • 1838- Darwin read Malthus essay where he found
    the answer to his question of how new species
    came to be (populations increase at a faster rate
    that do resources).
  • From this he inferred that in nonhuman animals,
    increase in population size is continuously
    checked by limited food supplies.
  • He accepted Lyells observation that in nature
    there is a constant struggle for existence.
  • It at once struck me that under these
    circumstances favourable variations would tend to
    be preserved, and unfavourable one to be
    destroyed. The result of this would be the
    formation of a new species (F Darwin, 1950, pp.
    53-54).

7
  • Alfred Rusell Wallace (1823-1913)- Born into a
    modest working class family.
  • Had little education.
  • 1848 he became interested in collecting plants
    and animals when he joined an expedition to the
    Amazon.
  • 1854 he sailed for Southeast Asia and the Malay
    Peninsula to continue his study and to collect
    bird and incest specimens.

8
  • In 1855, Wallace published a paper suggesting
    that species were descended from other species
    and that the appearance of new species was
    influenced by environmental factors.
  • 1858, Wallace sent Darwin a paper titled
  • On the Tendency of Varieties to Depart
    Indefinitely from the Original Type.
  • Urged by Lyell and others, in December 1859
    Darwin published his greatest work
  • On the Origin of Species by Means of Natural
    Selection, or the Preservation of Favored Races
    in the Struggle for Life.

9
Darwins Explanatory Model of Natural Selection
  • Fact 1 Every population has such high fertility
    that its size would increase exponentially if not
    constrained.
  • Fact 2 The size of populations, except for
    temporary annual fluctuation, remains stable over
    time (observed steady-state stability).

10
  • Fact 3 The resources available to every species
    are limited.
  • Inference 1 There is intense competition
    (struggle for existence) among members of a
    species.
  • Fact 4 No two individuals of a population are
    exactly the same (population thinking).
  • Inference 2 Individuals of a population differ
    from each other in the probability of survival
    (i.e., natural selection).
  • Fact 5 Many of the differences among the
    individuals of a population are, at least in
    part, heritable.
  • Inference 3 Natural selection, continued over
    many generations results in evolution.

11
Constraints on Nineteenth-Century Evolutionary
Theory
  • Darwin argued eloquently for the notion of
    evolution in general and the role of natural
    selection in particular, but he did not entirely
    comprehend the exact mechanisms for evolutionary
    change.
  • Natural selection acts on variation within a
    species.
  • However, no one understood the source of this
    variation.
  • Also, Darwin did no completely understand the
    mechanism by which parents transmitted traits to
    offspring.
  • Scholars of the time were confused about the laws
    of heredity, and the popular consensus was that
    inheritance was blending by nature.
  • As it turned out, the rules of heredity had
    already been worked out by an obscure Augustinian
    monk, Gregor Mendel.
  • However, this was not recognized until the
    beginning of the 20th century.

12
Opposition to Evolution
  • The topic of evolution was a hotly debated topic
    with On the Origin of Species turning the
    controversy into an inferno.
  • The very idea that species could give rise to
    other species was particularly offensive to many
    Christians because is was in direct conflict with
    events depicted in Genesis.
  • People were horrified that humans could be
    biologically related to other animal and
    especially that they might share a common
    ancestor with the great apes.

13
  • The mechanisms of evolution are complex and do
    not lend themselves to simple explanations.
  • Must have a strong background in biology and
    genetics.
  • While most religions offer explanations for
    natural phenomena, and some even feature the
    transformations of individuals from one form to
    another, none really proposes biological change
    over time.
  • 1996 Pope John Paul II issued a statement to the
    Pontifical Academy of Sciences acknowledging
    that
  • fresh knowledge leads to recognition of the
    theory of evolution as more than just a
    hypothesis.

14
Darwins Contributions
  • Lots of data
  • Changed focus from types to population and the
    variation in population
  • Mechanism for evolutionary change Natural
    Selection.
  • Data survival of the fittest
  • struggle/competition

15
  • Observations
  • Organisms reproduce more that their own numbers
  • Numbers remain fairly constant over time.
  • There is variation within and between species
  • Concluded competition and struggle for existence
    both within and between species.
  • Observed but could not explain
  • In this struggle for existence those organisms
    with favorable variation will live longer and
    thus reproduce more.
  • Natural Selection

16
(No Transcript)
Write a Comment
User Comments (0)
About PowerShow.com