Chapter 22 Part 2 Descent with Modification

Report
Concept 22.2: Descent with
modification by natural selection
explains the adaptations of
organisms and the unity and
diversity of life
• As the 19th century dawned, it was
generally believed that species had
remained unchanged since their creation
• However, a few doubts about the
permanence of species were beginning to
arise
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Darwin’s Research
• As a boy and into adulthood, Charles
Darwin had a consuming interest in nature
• Darwin first studied medicine
(unsuccessfully), and then theology at
Cambridge University
• After graduating, he took an unpaid
position as naturalist and companion to
Captain Robert FitzRoy for a 5-year
around the world voyage on the Beagle
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The Voyage of the Beagle
• During his travels on the Beagle, Darwin
collected specimens of South American
plants and animals
• He observed adaptations of plants and
animals that inhabited many diverse
environments
• Darwin was influenced by Lyell’s Principles
of Geology and thought that the earth
was more than 6000 years old
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Darwin
• His interest in geographic
distribution of species was kindled
by a stop at the Galápagos Islands
near the equator west of South
America
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Charles Darwin
• Father of the
modern theory
of evolution.
• Theory Descent with
Modification.
Darwin's Background
• Trained as a Naturalist (after trying
religion and medicine).
Voyage of the Beagle
Result
• Darwin's training and travel
opportunities allowed him to
formulate and support his ideas on
Natural Selection.
Fig. 22-5
GREAT
BRITAIN
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
AFRICA
Pinta
Marchena
Santiago
Fernandina
Isabela
Genovesa
Daphne
Islands
Pinzón
Santa
Cruz
Florenza
Santa
Fe
AUSTRALIA
PACIFIC
OCEAN
San
Cristobal
Española
Equator
SOUTH
AMERICA
Cape of
Good Hope
Tasmania
Cape Horn
Tierra del Fuego
New
Zealand
Darwin’s Focus on Adaptation
• In reassessing his observations,
Darwin perceived adaptation to the
environment and the origin of new
species as closely related processes
• From studies made years after
Darwin’s voyage, biologists have
concluded that this is indeed what
happened to the Galápagos finches
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Galapagos Finches
• In 1844, Darwin wrote an essay on the
origin of species and natural selection
but did not introduce his theory publicly,
anticipating an uproar
• In June 1858, Darwin received a
manuscript from Alfred Russell Wallace,
who had developed a theory of natural
selection similar to Darwin’s
• Darwin quickly finished The Origin of
Species and published it the next year
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Alfred Wallace - 1858
• Paper on Natural
Selection
identical to
Darwin's ideas.
Result - July 1, 1858
• Dual presentation of the WallaceDarwin ideas to the Linnaean
Society of London.
Darwin - 1859
• Publication of
"The Origin of
Species”
Comment
• Darwin best remembered for
the theory because of his
overwhelming evidence and
because he published.
The Origin of Species
• Darwin developed two main ideas:
–Descent with modification
explains life’s unity and
diversity
–Natural selection is a cause of
adaptive evolution
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Descent with Modification
• Darwin never used the word evolution in
the first edition of The Origin of Species
• The phrase descent with modification
summarized Darwin’s perception of the
unity of life
• The phrase refers to the view that all
organisms are related through descent
from an ancestor that lived in the remote
past
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Darwinian View
• History of life is like a tree with
branches over time from a common
source.
• Current diversity of life is caused
by the forks from common
ancestors.
• In the Darwinian view, the history of
life is like a tree with branches
representing life’s diversity
• Darwin’s theory meshed well with the
hierarchy of Linnaeus
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Example
“The Origin of Species”
• Documented the occurrence of
evolution.
• Suggested that the mechanism for
evolution was Natural Selection.
Artificial Selection, Natural
Selection, and Adaptation
• Darwin noted that humans have
modified other species by selecting
and breeding individuals with desired
traits, a process called artificial
selection
• Darwin then described four
observations of nature and from
these drew two inferences
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Fig. 22-9
Terminal
bud
Lateral
buds
Cabbage
Flower
clusters
Brussels sprouts
Leaves
Kale
Cauliflower
Stem
Wild mustard
Flowers
and stems
Broccoli
Kohlrabi
Observations:
Observation 1 – Members of a
population often vary greatly in
their traits.
.
Observation 2
• Traits are inherited
from parents to
offspring.
Observation 3
All species are
capable of
producing more
offspring than
their
environment
can support.
Observation 4
• Owing to lack of
food or other
resources, many
offspring do not
survive.
Inference 1
• Individuals whose inherited
traits give them a higher
probability of surviving and
reproducing in a given
environment tend to leave more
offspring than other
individuals.
Inference 2
• This unequal ability of
individuals to survive and
reproduce will lead to the
accumulation of favorable traits
in the population over
generations.
Nature
• Determines which characteristics
are favorable.
• Determines who survives.
• Result - “Natural Selection”
• Darwin was influenced by Thomas Malthus
who noted the potential for human
population to increase faster than food
supplies and other resources
• If some heritable traits are
advantageous, these will accumulate in
the population, and this will increase the
frequency of individuals with adaptations
• This process explains the match between
organisms and their environment
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Natural Selection: A Summary
• Individuals with certain heritable
characteristics survive and reproduce at
a higher rate than other individuals
• Natural selection increases the
adaptation of organisms to their
environment over time
• If an environment changes over time,
natural selection may result in adaptation
to these new conditions and may give rise
to new species
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Natural Selection in action
Fig. 22-12b
(b) A stick mantid
in Africa
• Note that individuals do not
evolve; populations evolve over
time
• Natural selection can only
increase or decrease heritable
traits in a population
• Adaptations vary with different
environments
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Artificial Selection
• When man determines the
characteristics that survive and
reproduce.
• Result - the various breeds of
animals and plants we’ve developed.
Example - Mustard Plant
Original
Cultivars (califlower,
brussel sprout, broccoli)
Example - dogs
Evolution Success Measured By
• Survival
• Reproduction
• Whoever lives long enough and has
kids is the “winner” in evolution.
Requirements
• In order for Natural Selection to
work, you must have:
–Inheritable Variations within a
population.
–Long periods of time (according
to Darwin).
Comment
• Acquired characteristics may allow
a species to evolve "outside" of
Natural Selection.
• Ex: culture, learning
Evidences for Evolution
• Direct observation of evolutionary
changes.
• Fossils
• Homology
• Convergent Evolution
• Biogeography
• Molecular
Discussion
• Why is it that individual organisms
cannot be said to evolve?
• Though an individual may become
modified during its lifetime through
interactions with its environment, this
does not represent evolution. Evolution
can be measured only as a change in
proportions of heritable variations from
generation to generation.
How does Darwin’s theory of
evolution relate to:
• Overproduction of populations?
• Limited resources?
• Heritable variation?
• Species have the potential to produce
more offspring than survive (overreproduction), leading to a struggle for
resources, which are limited. Populations
exhibit a range of heritable variations,
some of which confer advantages to their
bearers that make them more likely to
leave more offspring than less well-suited
individuals. Over time this natural
selection can result in a greater proportion
of favorable traits in a population
(evolutionary adaptation).
Next time….
Quiz
and
How Evolution is supported by
an overwhelming amount of
scientific evidence

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