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Title: Nerve activates contraction


1
Descent with Modification A Darwinian View of
Life
CH 22
Historical Context for Evolutionary Theory
1.Western culture resisted evolutionary views of
life 2.Theories of geologic gradualism helped
clear the path for evolutionary
biologists 3.Lamarck placed fossils in an
evolutionary context
2
Introduction
  • On November 24, 1859,
    Charles Darwin published
    On the Origin of Species by
    Means of Natural Selection.
  • Connecting what had once
    seemed a bewildering array
    of unrelated facts.
  • Two main points in The Origin of Species
  • Todays organisms descended from ancestral
    species.
  • Natural selection provided a mechanism for
    evolutionary change in populations.S

3
Western culture resisted evolutionary views of
life
  • The Origin of Species challenged a worldview that
    had been accepted for centuries.
  • The key classical Greek philosophers who
    influenced Western culture, Plato and Aristotle,
    opposed any concept of evolution.
  • Plato believed in two worlds one real world that
    is ideal and perfect and an illusory world of
    imperfection that we perceive through our senses.
  • Aristotle believed that all living forms could be
    arranged on a ladder (scala naturae) of
    increasing complexity with every rung taken with
    perfect, permanent species. Species are permanent
    and do not change.

4
  • In the 1700s, the dominant philosophy, natural
    theology, was dedicated to studying the
    adaptations of organisms as evidence that the
    Creator had designed each species for a purpose.
  • Carolus Linnaeus, a Swedish botanist, developed
    taxonomy, a system for naming species and
    grouping species into a hierarchy of increasingly
    complex categories.
  • He believed that classification would reveal a
    divine plan.

Carolus Linnaeus (1707-1778)
5
  • Darwins views were influenced by fossils, the
    relics or impressions of organisms from the past,
    mineralized in sedimentary rocks.
  • Sedimentary rocks form when mud and sand settle
    to the bottom of seas, lakes, and marshes.
  • New layers of sediment cover older ones, creating
    layers of rock called strata.
  • Fossils within layers show that a succession of
    organisms have populated Earth throughout time.

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Paleontology, the study of fossils, was largely
developed by Georges Cuvier, a French
anatomist. -realized that each stratum of earth
is characterized by different fossils.
  • Cuvier recognized that extinction had been a
    common occurrence in the history of life.
  • Instead of evolution, Cuvier advocated
    catastrophism, that boundaries between strata
    were due to local flood or drought that destroyed
    the species then present.
  • Later, this area would be repopulated by species
    immigrating from other unaffected areas.
  • Strongly opposed evolution.

8
Theories of geologic gradualism helped clear the
path for evolutionary biologists
  • In contrast to Cuviers catastrophism, James
    Hutton, a Scottish geologist, proposed a theory
    of gradualism in 1795.
  • Earth had been molded, not by sudden, violent
    events, but slow, gradual change
  • Wind, water and weather formed the Earth.
  • Proposed that the Earth was VERY old.

James Hutton
9
  • Later, Charles Lyell, a geologist, proposed a
    theory of uniformitarianism.
  • Geological processes had not changed throughout
    Earths history.
  • Earth was very old!

Charles Lyell
Uniformitarianism is the assumption that the
natural processes operating in the past are the
same as those that can be observed operating in
the present
-contrast with catastrophism
10
  • Huttons and Lyells observations and theories
    had a strong influence on Darwin.
  • First, if geologic changes result from slow,
    continuous processes, rather than sudden events,
    then the Earth must be far older than the 6,000
    years assigned by theologians from biblical
    inference.
  • Second, slow and subtle processes persisting for
    long periods of time can add up to substantial
    change.

11
Lamarck placed fossils in an evolutionary context
  • In 1809, Jean Baptiste Lamarck published a theory
    of evolution based on his observations of fossil
    invertebrates in the Natural History Museum of
    Paris.
  • Lamarck thought that he saw what appeared to be
    several lines of descent in the collected fossils
    and current species.
  • Each was a chronological series of older to
    younger fossils leading to a modern species.

1809-Darwin was born
12
  • Central to Lamarcks mechanism of evolution were
    the concepts of use and disuse of parts and of
    inheritance of acquired characteristics.
  • Proposed that body parts used extensively to cope
    with the environment became larger and stronger,
    while those not used deteriorated.
  • These modifications acquired during the life of
    an organism could be passed to offspring.
  • A classic example of these is the long neck of
    the giraffe.

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Inheritance of Acquired Characteristics
  • Lamarcks theory was a visionary attempt to
    explain both the fossil record and the current
    diversity of life through its recognition of the
    great age of Earth and adaptation of organisms to
    the environment.
  • However, there is no evidence that acquired
    characteristics can be inherited.
  • A lizard that didn't use it legs would eventually
    not have legs and its offspring wouldn't have
    legs
  • A giraffe stretched its neck to reach higher
    leaves, and this stretched neck would be a trait
    inherited by its offspring
  • Acquired traits (e.g., bigger biceps) do not
    change the genes transmitted by gametes to
    offspring.

15
Alfred Russel Wallace -1858-emphasis was based on
the idea of competition for resources as the main
force in natural selection
  • He independently proposed a theory of natural
    selection which prompted Charles Darwin to
    publish his own more developed and researched
    theory sooner than he had intended.
  • Father of biogeography".

January 8, 1823 November 7, 1913
  • Publications
  • Wallace, Alfred Russel (2000 originally
    published 1869). The Malay Archipelago.
    Singapore Periplus Press. ISBN 962-593-645-9.
  • Wallace, Alfred Russel (1870). Contributions to
    the Theory of Natural Selection.
  • Wallace, Alfred Russel (1876). The Geographical
    Distribution of Animals.
  • Wallace, Alfred Russel (1898). Vaccination A
    Delusion. Swan Sonnenschein Co.

16
  • Charles Darwin (1809-1882) was born in western
    England.
  • While Darwin had a consuming interest in nature
    as a boy, his father sent him to the University
    of Edinburgh to study medicine.
  • Darwin left Edinburgh without a degree and
    enrolled at Christ College at Cambridge
    University with the intent of becoming a
    clergyman.
  • At that time, most naturalists and scientists
    belonged to the clergy and viewed the world in
    the context of natural theology.

CLIP
Edinburgh
Cambridge
17
  • Darwin received his degree in 1831.
  • After graduation Darwin was recommended to be the
    conversation companion to Captain Robert FitzRoy,
    who was preparing the survey ship HMS Beagle for
    a voyage around the world.
  • FitzRoy chose Darwin because of his education,
    and because he was of the same social class, and
    was close in age to the captain.

18
Field research helped Darwin frame his view of
life
  • The main mission of the five-year voyage of the
    Beagle was to chart poorly known stretches of the
    South American coastline.

19
Darwin had the freedom to explore extensively on
shore while the crew surveyed the coast.
  • He collected thousands of specimens of the exotic
    and diverse flora and fauna of South America.
  • Darwin explored the Brazilian jungles, the
    grasslands of the Argentine pampas, the
    desolation of Tiera del Fuego, and the heights of
    the Andes.

20
  • Darwin noted that the plants and animals of South
    America were very distinct from those of Europe.
  • Organisms from temperate regions of South America
    were more similar to those from the tropics of
    South America than to those from temperate
    regions of Europe.
  • Further, South American fossils more closely
    resembled modern species from that continent than
    those from Europe.

21
  • The origin of the fauna of the Galapagos, 900 km
    west of the South American coast, especially
    puzzled Darwin.
  • Darwin noted that while most of the animal
    species on the Galapagos lived nowhere else, they
    resembled species living on the South American
    mainland.

22
  • While on the Beagle, Darwin read Lyells
    Principles of Geology.
  • Lyells ideas and his observations on the voyage
    led Darwin to doubt the churchs position that
    the Earth was static and only a few thousand
    years old.
  • Instead, he was coming to the conclusion that the
    Earth was very old and constantly changing.

23
  • After his return to Great Britain in 1836, Darwin
    began to perceive that the origin of new species
    and adaptation of species to the environment were
    closely related processes.
  • For example, clear differences in the beak among
    the 13 types of finches that Darwin collected in
    the Galapagos are adaptations to the foods
    available on their home islands.

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  • By the early 1840s Darwin had developed the major
    features of his theory of natural selection as
    the mechanism for evolution.
  • In 1844, he wrote a long essay on the origin of
    species and natural selection, but he was
    reluctant to publish his theory and continued to
    compile evidence to support his theory.
  • In June 1858, Alfred Wallace, a young naturalist
    working in the East Indies, sent Darwin a
    manuscript containing a theory of natural
    selection essentially identical to Darwins.

Alfred Wallace
27
The Origin of Species developed two main points
  1. Evolution is the explanation for lifes unity and
    diversity.
  2. Natural selection is the cause of adaptive
    evolution.

the occurrence of evolution and natural
selection as its mechanism
28
Central to Darwins view of the evolution of life
is descent with modification
  • All present day organisms are related through
    descent from unknown ancestors in the past.

Descendents of these ancestors accumulated
diverse modifications or adaptations that fit
them to specific ways of life and
habitats.
29
This evolutionary tree of the elephant family is
based on evidence from fossils.
Descent with modification
30
The other major point that Darwin pioneered is a
unique mechanism of evolution - the theory of
natural selection.
  • Darwins main ideas can be summarized as
    follows.
  • Populations tend to grow exponentially,
    overpopulate, and exceed their resources.
  • Overpopulation results in competition and
    struggle for existence.
  • In any population, there is variation and an
    unequal ability of individuals to survive and
    reproduce.
  • Only the best-fit individuals survive and get to
    pass on their traits to offspring.
  • Evolution occurs as advantageous traits
    accumulate in a population.

31
For example, related species of insects called
mantids have diverse shapes and colors that
evolved in different environments.
32
  • In each generation, environmental factors
    filter heritable variations, favoring some
    over others.
  • Differential reproduction -- whereby organisms
    with traits favored by the environment produce
    more offspring than do organisms without those
    traits -- results in the favored traits being
    disproportionately represented in the next
    generation.
  • This increasing frequency of the favored traits
    in a population is evolution.

33
Peppered Moth
  • Two versions of the moth-
  • Black and peppered
  • During the industrial revolution on England
  • Population of moths changed

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  • Darwins views on the role of environmental
    factors in the screening of heritable variation
    were heavily influenced by artificial selection.
  • Humans have modified a variety of domesticated
    plants and animals over many generations by
    selecting individuals with the desired traits as
    breeding stock.

36
Natural selection can only amplify or diminish
heritable variations, not variations that an
individual acquires during its life, even if
these variations are adaptive.
37
  • In general, natural selection operates not to
    create variation, but to edit existing variation.
  • For example, resistant insects are favored and
    non-resistant individuals are not when
    insecticides are applied.
  • Natural selection favors those characteristics in
    a variable population that fit the current, local
    environment.

38
Other evidence of evolution
  • Fossil record

39
Rock layer
40
Isotope dating-radioactive dating
  • Half-life
  • 14C
  • Earth
  • 4.6 billion years old

41
Comparative Anatomy
42
Homologous structures
Reflect common ancestry
  • Anatomical similarities between different
    species.
  • Ex forelimbs of human, cats, whales, and bats
    share the same skeletal elements, but different
    functions because they
    diverged from their

    common
    ancestor.

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Analogous structures
  • Bats wing and a flys wing have the same
    function However they have different ancestors.
  • They have simply adapted to similar environments.
  • Convergent evolution

45
  • While the sugar glider and flying squirrel have
    adapted to the same mode of life, they are not
    closely related.
  • Instead, the sugar glider from Australia is more
    closely related to other marsupial mammals from
    Australia than to the flying
    squirrel, a placental
    mammal from North America.
  • The resemblancebetween them is
    another example
    ofconvergentevolution.

Analogous structures
46
Vestigial structures
  • Structures that have marginal, if any, importance
    to a current organism, but which had important
    functions in ancestors.

They are usually reduced in size
47
Vestigial structures
  • Whale pelvis

48
Comparative Embryology
  • Similar stages in embryonic development.
  • Ex All vertebrates embryos go through a stage in
    which they have gill pouches on the sides of the
    throats.
  • Fish-gills
  • Humans-eustachian . tubes

49
Comparative Embryology
  • Sometimes, homologies that are not obvious in
    adult organisms become evident when we look at
    embryonic development.
  • For example, all vertebrate embryos have
    structures called pharyngeal pouches in their
    throat at some stage in their development.
  • These embryonic structures develop into very
    different, but still homologous, adult
    structures, such as the
  • gills of fish or
  • the Eustacean tubes that connect the middle ear
    with the throat in mammals.

50
Molecular Biology
51
Molecular Biology
  • Molecular biology allows links between organisms
    that have no macroscopic anatomy in common
  • All species of life have the same basic genetic
    machinery of RNA and DNA and the genetic code is
    essentially universal.
  • -The language of the genetic code has been passed
    along through all the branches of the tree of
    life ever since the codes inception in an early
    life-form.
  • All aerobic organism contain the polypeptide
    cytochrome C
  • -Amino acids sequence of CytoC can show how
    closely related two species are.

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The geographical distribution of species --
biogeography -- first suggested evolution to
Darwin.
55
Theory of Continental drift 200mya-Pangaea Today-
7 continents Wagner
56
  • Species tend to be more closely related to other
    species from the same area than to other species
    with the same way of life, but living in
    different areas.
  • For example, even though some marsupial mammals
    (those that complete their development in an
    external pouch) of Australia have look-alikes
    among the eutherian mammals (those that complete
    their development in the uterus) that live on
    other continents, all the marsupial mammals are
    still more closely related to each other than
    they are to any eutherian mammal.

eutherian mammals
57
Distribution of Living Species
Beaver
Beaver Muskrat Beaver andMuskrat Coypu
Capybara Coypu andCapybara
NORTH AMERICA
Muskrat
Capybara
SOUTH AMERICA
Coypu
58
  • Island and island archipelagos have provided
    strong evidence of evolution.
  • Often islands have many species of plants and
    animals that are endemic, or found nowhere else
    in the world.
  • As Darwin observed when he reassessed his
    collections from the Beagles voyage, these
    endemic species are typically related more
    closely to species living on the nearest mainland
    (despite different environments) than those from
    other island groups.

59
  • All of the 500 or so endemic species of
    Drosophila in the Hawaiian archipelago descended
    from a common ancestor that reached Kauai over 5
    million years ago.

60
All of that being said, be aware that..
  • Natural selection is widely accepted in science
    because its predictions have withstood thorough,
    continual testing by experiments and
    observations.
  • However, science is not static and arguments
    exist among evolutionary biologists concerning
    whether natural selection alone accounts for the
    history of life as observed in the fossil record.
  • The study of evolution is livelier than ever, but
    these questions of how life evolves in no way
    imply that most biologists consider evolution
    itself to be just a theory.

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Timeline
63
BC Aristotle Species are permanent, arranged on a ladder.
1700s Carolus Linnaeus Taxonomy, classification shows relationships, classification would reveal a divine plan
1700s Georges Cuvier Studied fossils, opposed evolution, catastrophes responsible for changes in organisms
1795 James Hutton Gradualism, Earth molded by weather, Earth has a long history
1798 Thomas Malthus Populations outgrow their food supplies, causing competition
1809 Jean Baptiste Lamarck Inheritance of acquired characteristics.
1833 Charles Lyell Geologist, Earth more than 6,000 years old, Principles of Geology, uniformitarianism
1858 Alfred Russel Wallace Proposed natural selection as the mechanism for evolution
1859 Charles Darwin Theory of Natural Selection, On the Origin of the Species by Natural Selection
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