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Charles Darwin 18091882

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Charles Darwin. 1809-1882. Descent with Modification. And the Origin of Species. Charles Darwin at age 31. Born 12 February 1809 ... – PowerPoint PPT presentation

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Title: Charles Darwin 18091882


1
Charles Darwin1809-1882
  • Descent with Modification
  • And the Origin of Species

2
Born 12 February 1809
Charles Darwin at age 31
3
(No Transcript)
4
Full-scale replica of the Beagle sailing off the
coast of South America.
General plan of the Beagle based on a drawing by
a shipmate during the voyage of the Beagle.
Darwin wrote that, I have just room to turn
around and that is all.
5
Voyage of HMS Beagle 1831-1836
A five year, circumnavigation of the globe, with
the principal objective to map the coast line of
South America.
6
Darwins Finches
Galapagos Islands
7
.
Voyage of HMS Beagle 1831-1836
A five year, circumnavigation of the globe, with
the principal objective to map the coast line of
South America.
8
The Darwinian Thesis
Fact 1. Organisms have enormous reproductive
potential (Malthus)
Numbers
Exponential growth
Time
Fact 2. Populations are at equilibrium
(Observation)
Logistic Growth
Numbers
Time
9
Fact 3. Resources are limited (0bservation).
If organisms have enormous reproductive
potential, yet do not realize that potential
owing to the fact that resources are limited,
then there must be .
Inference 1. a struggle for existence.
Fact 4. Individuals are unique there is
individual variation. (Observation)
Variation in shell color and banding pattern
within a single species of Caribbean
snail. Darwin was impressed with the fact that no
two individuals are exactly alike. In contrast
to the Platonic idea that the eternal idealized
type was what mattered, Darwin made individual
variation an integral part of his theory of
evolutionary change.
10
Inference 2. If there is a struggle for existence
and there is individual variation, then some
individuals, owing to their unique set of traits,
will be better equipped to prevail in the
struggle for existence. In other words, NATURE
SELECTION will occur.
Fact 5. Some individual variation can be
transmitted from one generation to the next
(personal observation, experience with animal
breeding).
Offspring resemble their parents, but not
precisely. Thus, differences among individuals in
the parental generation tend to be reflected in
individuals of the descendent generation.
Trait in Offspring
Trait in Parents
11
Within species, each individual is unique. That
is, for most biological traits there is
individual variation. But what are the sources of
this variation?
Imagine that you take a sample of Mockingbirds
from the population that exists on the University
of Miami campus.
You measure and record bill length on several
hundred specimens, and then cast your data into a
frequency distribution, just as instructors cast
test scores into a frequency distribution (the
curve) for purposes of assigning grades.
Northern Mockingbird
12
Why arent all of the mockingbirds identical with
respect to bill length? That is, what are the
sources of variation in bill length in this
population?
Frequency
Bill Length
Sources of Variation
  • Sexual Dimorphism -- differences due to sex
  • Ontogenetic Variation -- differences due to age
  • Environmental Effect -- differences due to
    environment
  • Artifactual Variation -- Imprecision in
    measurement
  • Genetic Variation -- Variation due to genetic
    differences among individuals

13
Parental Generation
Only birds with large bills are allowed to
reproduce and thus contribute to the next
generation
Frequency
By selecting birds with large bills to produce
the next generation, we get a statistical
response to this artificial selection on average
bill length in the descendent birds exceeds that
of the parental generation. In addition, some
individuals in the offspring generation exceed
any in the parental generation in bill length.
Offspring
Frequency
14
Inference 3. Natural selection, operating over
the immensity of Geologic time, will produce
evolutionary change, or DESCENT WITH
MODIFICATION, to use Darwins expression.
IN SUMMARY According to the Darwinian Thesis,
evolution proceeds by means of agents of natural
selection, operating on heritable variation
within populations, to bring about
ancestor-descendant change.
That substantial changes can be induced in plants
and animals by artificial selection is obvious.
Consider the many very different breeds of dogs,
all descended from a single ancestral species
(the wolf). But can we find examples of natural
selection operating in nature?
15
Natural Selection in the House Sparrow, Passer
domesticus.
  • Native to Europe
  • Introduced into North America
  • at New York ca. 1850
  • Spread Across North America,
  • arriving in California by 1910
  • Presently ranges from northern
  • Canada to Oaxaca, Mexico
  • A human commensal, hence the
  • specific name, domesticus.

16
On 1 February 1898, in Providence, Rhode Island,
an unusually severe winter storm killed or
incapacitated a large number of House Sparrows.
  • One hundred-thirty-four dead or moribund house
    sparrows were brought to the laboratory of
    Professor Herman Bumpus.
  • He divided the birds into those that were dead
    (non-survivors) and those that were alive when he
    received them (survivors).
  • He then weighed each bird, measured total length
    and wing-span.
  • He skeletonized all birds (survivors
    non-survivors), so in truth there were no
    survivors. He measured various skeletal
    elements including those from the head, body, and
    appendages.
  • He searched for differences in size and shape
    between survivors versus non-survivors.
  • Bumpus published all of his original
    measurements.

17
Re-analysis of Herman Bumpus House Sparrow Data
at the University of Kansas Dr. Richard F.
Johnston et al.
  • Eliminated mass, wing-span and total length from
    analysis for being too imprecise in terms of
    measurement.
  • Analyzed on the basis of skeletal measurements
    on the body, skull, and appendages
  • Used a statistical analysis that combined the
    information contained in all of the measurements
    into a single over-all measure of size.
  • Analyzed the sexes separately, as House Sparrows
    are known to exhibit sexual dimorphism, with
    males slightly larger, on average, than females.

18
Results of the Re-analysis of the Bumpus Data
Males
Females
Small
Large
Small
Large
19
Males
Likelihood of Surviving
Low
Medium
High
Very High
Larger
Smaller
Body Size
Directional Selection favoring large body size in
male House Sparrows.
20
Selection in which individuals in one tail of
the curve of variation have higher likelihood of
survival (are selected for) is termed
directional selection because over many
generations, the average value of the trait (in
this case body size), will shift in the same
direction. Thus, in the Bumpus example,
directional selection was operating on male House
Sparrows to favor those with large body size.
Selection which operates more or less equally
on both tails of the curve of variation is called
stabilizing, or normalizing selection because
under this mode of selection, the average value
of the trait does not change. Variation in the
trait will be reduced, however. In the Bumpus
example, stabilizing selection was operating on
females, favoring those of intermediate body
size. A third mode of selection, disruptive
selection, occurs when individuals of
intermediate value have a lower likelihood of
surviving relative to those at either end of the
curve of variation. This is termed disruptive
selection.
21
Results of the Re-analysis of the Bumpus Data
Males
Females
Small
Large
Small
Large
22
Females
Likelihood of Surviving
Very High
High
Medium
Low
Larger
Body Size
Stabilizing Selection favoring intermediate body
size in House Sparrows.
23
Selection in which individuals in one tail of
the curve of variation have higher likelihood of
survival (are selected for) is termed
directional selection because over many
generations, the average value of the trait (in
this case body size), will shift in the same
direction. Thus, in the Bumpus example,
directional selection was operating on male House
Sparrows to favor those with large body size.
Selection which operates more or less equally
on both tails of the curve of variation is called
stabilizing, or normalizing selection because
under this mode of selection, the average value
of the trait does not change. Variation in the
trait will be reduced, however. In the Bumpus
example, stabilizing selection was operating on
females, favoring those of intermediate body
size. A third mode of selection, disruptive
selection, occurs when individuals of
intermediate value have a lower likelihood of
surviving relative to those at either end of the
curve of variation. This is termed disruptive
selection.
24
Selection in which individuals in one tail of
the curve of variation have higher likelihood of
survival (are selected for) is termed
directional selection because over many
generations, the average value of the trait (in
this case body size), will shift in the same
direction. Thus, in the Bumpus example,
directional selection was operating on male House
Sparrows to favor those with large body size.
Selection which operates more or less equally
on both tails of the curve of variation is called
stabilizing, or normalizing selection because
under this mode of selection, the average value
of the trait does not change. Variation in the
trait will be reduced, however. In the Bumpus
example, stabilizing selection was operating on
females, favoring those of intermediate body
size. A third mode of selection, disruptive
selection, occurs when individuals of
intermediate value have a lower likelihood of
surviving relative to those at either end of the
curve of variation. This is termed disruptive
selection.
25
Likelihood of Surviving
Very High
High
Medium
Low
Trait Value
26
Modes of Natural Selection
  • Directional selection mean changes, variation
    is reduced (e.g., male House Sparrows in the
    Bumpus example).
  • Stabilizing selection mean does not change,
    variation reduced (e.g., female House Sparrows in
    the Bumpus example).
  • Disruptive selection mean does not change,
    variation increased.

27
Historical Narrative Tracing the Development
of Darwins Ideas Concerning the Mechanism of
Evolutionary Change (cont.d.)
  • 1842 -- Brief unpublished abstract
  • 1844 -- Unpublished essay of about 250 pages
  • 1858 -- Received manuscript by Alfred Russel
    Wallace entitled On the Tendency of Varieties
    to Depart Indefinitely from the Ancestral Type.
  • 1858 -- Joint presentation of the theory of
    evolution by natural selection before the Royal
    Linnaean Society of London.
  • 1859 -- Publication of On the Origin of
    Species by Means of Natural Selection, or The
    Preservation of Favored Races in the Struggle
    for Life.
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