Transcript descent with modification: a darwinian view of life

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CHAPTER 22
DESCENT WITH
MODIFICATION: A
DARWINIAN VIEW OF LIFE
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EVOLUTION
Evolution is defined as change over time in
the genetic composition of a population
(not an individual)
Most attention given to Charles Darwin’s
On the Origin of Species by Means of
Natural Selection (November 24, 1859)
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CONCEPT 22.1: Pre-Darwinian Views
A. Creationism (Scala Naturae)
Aristotle’s philosophy
Aristotle opposed any concept of evolution
Viewed species as fixed and unchanging
All living forms could be arranged on a ladder of
increasing complexity with each perfect,
permanent species having its own rung
Strict belief in the Book of Genesis and creation
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B. Natural Theology
Viewed the adaptations of organisms as evidence
that the Creator had designed each species for a
purpose
Major follower—Carolus Linnaeus (1707-1778)
--developed hierarchy of taxonomic categories
based morphology and anatomy
--did not believe in evolution
--taxonomic system became the focal point of
Darwin’s arguments for evolution
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C. Catastrophism
Georges Cuvier, French anatomist and
paleontologist and father of paleontology (study of
fossils)
Based on fossils found in sedimentary rock strata
Idea that the boundaries between strata were due
to local catastrophic events (fires, floods, volcano
eruptions, droughts) that destroyed the species
then present
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Cuvier proposed the theory of
catastrophism to reconcile
fossil evidence and his antievolutionary background
Proposed that catastrophes
were localized and regions were
repopulated by species
immigrating from unaffected
areas
Opposed idea of gradual
evolutionary change
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D. Gradualism
James Hutton, geologist
Change is cumulative product of slow continuous
natural processes identical to those currently
operating
Competitive with Cuvier’s theory
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E. Uniformitarianism
Charles Lyell
Expansion on gradualism
Geological processes had
not changed throughout
Earth’s history
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F. Darwin was strongly influenced by
Gradualism and Uniformitarianism and
reasoned that:
Earth must be older than 6000 years.
Slow and subtle processes can act on
living organisms producing substantial
change over a long period of time.
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G. Lamarckism
Jean Baptiste Lamarck (1744-1829)
Mechanism:
1. Use and Disuse
--body organs used become stronger/larger
--those not used deteriorated
2. Inheritance of Acquired Characteristics
--changes acquired during a lifetime are passed on
to offspring
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Lamarck
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II. Concept 22.2: Charles Darwin
A. The Voyage of the Beagle
Sailed from England in December of 1831 to
chart South American coastline
Darwin Noted:
1. Geographical distribution of species
2. On the Galapagos Islands he collected
several different kinds of finches that
were similar but seem to be different
species
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Voyage of the Beagle (December 1831-October 1836)
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B. The Book
1. Darwin perceived the origin of new species and
adaptation as closely related processes
2. Formulated theory by early 1840’s
3. 1844 wrote essay on origin of species and
natural selection but did not publish
4. June 1858 received Alfred Wallace’s manuscript
on evolution and natural selection
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Wallace
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5. Both papers (Darwin and Wallace) presented by Lyell to
Linnaean Society of London on July 1, 1858
6. Darwin published Origin of the Species in 1859
7. Two main ideas of the book:
a. Species evolved from ancestral species; not
specially created
b. Mechanism for evolutionary change—
natural selection
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C. Principle of Common Descent
1. In the 1st edition, he used term “descent with
modification” instead of evolution.
2. Modifications occur as organisms moved into
new habitats or as habitats changed
3. Viewed history of life as a tree with most
branches evolutionary dead ends
4. Common ancestors at each fork
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Phylogenetic Tree
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Logic of Darwin’s Theory of Natural Selection
1. All species have potential fertility to show
exponential growth in a population if all
reproduced successfully.
2. Populations tend to remain stable in size, except
for seasonal fluctuations.
3. Resources are limited.
4. Individuals of population vary extensively.
5. Much of this variation is heritable.
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Three conclusions:
1. Production of more organisms than can survive
leads to a struggle for survival.
2. Survival isn’t random, but depends on heredity.
3. Unequal ability to survive and reproduce will
lead to gradual change in a population with
favorable characteristics accumulating over
generations.
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D. Natural Selection
1. Natural selection is the differential success in
reproduction that results from the interaction
between individuals that vary in heritable traits
and their environment.
2. Thomas Robert Malthus’s Essay on the Principles of
Population (1798) outlined a “struggle for existence”
and heavily influenced Darwin’s views on “over
reproduction.”
3. Natural selection is made possible by:
a. Variation
b. Over reproduction
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4. Important Facts About Natural Selection:
A population (group of interbreeding individuals of
the same species in the same geographic area) is the
smallest unit that can evolve.
Natural selection can amplify or diminish only
heritable variations.
Natural selection is always operating, but which
traits are favored depends on the environment.
5. Example of Natural Selection: antibiotic resistance in
bacteria
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III. Concept 22.3: Scientific
Evidence to Support Evolution
1. Artificial Selection
Striking differences can occur in a very short time
if one selects which organisms reproduce.
2. Biogeography
Geographical distribution of species
Pangea
Endemic species
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3. Fossil Record
Missing links gradually being filled in
Shows chronological appearance of
vertebrates (fish, amphibians, reptiles, birds,
mammals)
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Artificial Selection
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4. Taxonomy
Linnaeus’ taxonomic scheme reflected the genealogy
of the tree of life
5. Comparative Anatomy
a. Anatomical similarities between species in same
taxonomic group show evidence of common descent
b. Based on homologous and vestigial structures
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homologous structures-represent variations on a
structural theme that was present in their common
ancestor
-Ex: skeleton elements of mammalian forelimbs
vestigial organs-remnants of structures that served
important functions in the organism’s ancestors
-Ex: pelvic and leg bones in snakes; human appendix
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Homologous Structures
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convergent evolution—refers to the
development of structures which have a
similar function but develop differently and
appear unrelated
Leads to analogous structures meaning
they have similar functions but not
common ancestry
Ex: sugar glider and flying squirrel
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6. Comparative Embryology
Defined as the comparison of early stages of
animal development
Closely related organisms go through similar stages
Ex: all vertebrate embryos have pharyngeal
pouches and a tail at some time
“Ontogeny recapitulates phylogeny.” Embryonic
development (ontogeny) is a replay of the
evolutionary history of the species (phylogeny).
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Comparative Embryology
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Evolutionary tree
Evolutionary trees are diagrams that reflect
evolutionary relationships among groups of
organisms
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7. Molecular Biology
Hereditary background is reflected in genes
and protein products.
Since the genetic code is shared by all
organisms, it is likely that all species
descended from a common ancestor
Closer the relationship, the higher the
percentage of common DNA.
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Molecular Biology
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You should now be able to:
1. Describe the contributions to evolutionary theory
made by Linnaeus, Cuvier, Lyell, Lamarck,
Malthus, and Wallace
2. Describe Lamarck’s theories, and explain why
they have been rejected
3. Explain what Darwin meant by “descent with
modification”
4. List and explain Darwin’s four observations and
two inferences
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5. Explain why an individual organism cannot evolve
6. Describe at least four lines of evidence for
evolution by natural selection
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