Transcript Power Point Presentation

How Populations Evolve
 Jean-Baptiste

Traits acquired during
lifetime are inheritable
 Charles
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Lyell
Geologic change is the
steady accumulation of
changes over a long
period of time
 Alfred
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Lamarck
Wallace
Contemporary of Charles
Darwin
Conceived theory very
similar to Darwin
 Attended
Cambridge for
religious studies
 Biologist on HMS Beagle in
1831
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Studied plants, animals, fossils
Influenced by Lyell’s geology
ideas
 Consulted
1850s
with Wallace in
 1859—Published
On the
Origin of Species by
Means of Natural
Selection
 Immediate controversy,
continues today
 Members
of a population vary in traits, traits
are inheritable
 Species produce more offspring than an
environment can support
 Individuals with traits that give them a
better chance of survival & reproduction will
tend to leave more offspring
 Unequal production of offspring will cause
these traits to increase in a population over
generations
 Fossils
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Older fossils deeper in strata
of rocks
Older fossils show less
variation
Older fossils show less
complex features
Younger fossils show more
variation and more complex
features
Younger fossils have
characteristics more like
living organisms
 Biogeography
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Study of geographical
distribution of species
If species have similar
characteristics but are in
different locations, can
infer that there was a
common ancestor from
which each evolved
Used with idea of
continental drift
 Comparative
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Anatomy
Homologous structures—different functions but
similar structure. Theorized to be due to common
ancestry
 Comparative

Anatomy
Vestigial structures—structures with little or no
importance to organism. Theorized to be
previously important organ that organisms
evolved out of needing

Some structures now seen to have uses and may not be
“vestigial”
 Molecular

Biology
Many organisms have similar DNA
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Comparable DNA to humans….
 Other humans 99+%
 Chimpanzees—95-98%
 Fruit flies—60%
 Bananas—50%
However, the similarities depend on
how the analysis is performed (see
this article or this one)
 New
alleles and phenotypes originate by
mutation
 Most mutations are harmful or neutral
 Some may confer some benefits
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For examples, see this article
 Mutations
provide the variety in traits
needed by Darwin’s description of natural
selection
 Beneficial mutations may increase
survivability
 Genetic
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Drift—change in a gene pool due to chance
Smaller populations more quickly and strongly affected
 Bottleneck
Effect—Sudden and extreme event that
leaves a small population
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Flood, fire, earthquake, disease, etc.
Unlikely to have same genetic makeup of original
population
 Any
given trait has variations within a
population
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Height, hair color, tail length, beak thickness,
immune response, etc.
 Variations
tend to follow a “bell curve”
 Stabilizing
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Selection
Favors intermediate phenotypes
Selects against extremes
Human birth weight
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Too large or too small increase risk for baby’s survival
 Directional
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Selection
Moves traits in direction of one phenotype
extreme
Selects against other extreme
Coloration to allow better camoflague
 Disruptive
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Selection
Individuals at both extremes selected for
Intermediate forms selected against.
Galapagos finch beak size
 Organisms
with certain
physical traits are more
likely than others to
obtain mates
 Some traits may compete
with other factors of
natural selection
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Fighting for a mate may
result in injury and death
Some physical traits (e.g.
extremely large or long
tails) may make survival
difficult