BLG 144 Lecture Notes - Lecture 2: Allele Frequency, James Hutton, Body Plan

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5 May 2015

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Evolution by Natural Selection
Plato – typological thinking: species are unchanging types and that variations within species
are unimportant or even misleading.
Aristotle – The Great Chain of Being (Ladder of Nature):
Species were organized into a sequence based on increased size and complexity
(Humans ^)
Characteristics of species were fixed- they did not change through time
Despite similar environments, different regions have distinct plants and animals
Asserted that climate change facilitated the worldwide spread of species from their
centers of origin
James Hutton
Theory of Gradualism: change is gradual and in slow processes, happening over a long
period of time
The earth we see today is the result of slow gradual changes over time
The growth of population will always outrun its ability to feed itself
If every couple raised 4 children, the population would increase geometrically by factors
of 4
Looked at humans as a group (population)
Lamarck – Idea of Evolution as Change through Time
Organisms originate spontaneously then evolve into more complex and “better” species
Inheritance of Acquired Characters: Individuals change in response to their environment
and then pass on those changes to their offspring.
Example: Giraffes acquire long necks while reaching high into the trees, then pass on
long neck to their offspring
Variation is acquired
Use and disuse: The more you use your muscles, the more strong you become, you
pass on the strength to your offspring
Charles Lyell
Used geological proofs that the earth was older than 6000 years
Darwin and Wallace - Evolution by Natural Selection
Traits vary amongst individuals
Individuals with certain traits leave more offspring
Population: individuals of the same species living the same area at the same time
Population thinking rather than typological thinking
Evolution by Natural Selection states:
1. Species change through time
2. Species are related by common ancestry
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The Origin of Species basic ideas:
1. All organisms have descended with modification from common ancestors
2. The major agent of modification is natural selection operating on variation among
Why the theory of evolution was revolutionary:
1. Overturned the idea that species were static and unchanging
2. Replaced typological thinking with population thinking
3. It was Scientific: accounted for change through time and made predictions that could be
further tested
Decent with modification: change over time produced modern species that are modified from
ancestral species
How does Natural Selection Work:
1. There is variation within the population, with genes and traits
2. This Variation is heritable
3. There are limited resources > unequal reproductive success
4. Individuals that are best adapted to the environment will have high reproductive success,
leave more offspring
Evolution: change of allele frequency over time
Evolution by natural selection occurs when individuals with certain alleles produce the most
surviving offspring
Adaptation: > genetically based trait > increases one’s ability to produce offspring in a
particular environment
Evolution does not change the characteristics of an individual but of a population
Animals don’t do things for the good of the species
Not all traits are adaptive
Adaptations are constrained by tradeoffs, genetic and historical factors
Evidence of Evolution
1. Species have changed over time
Geology: change in Earth, Age of Earth, Age of Life
Radiometric Dating: observed decay rates of parent to daughter atoms
Ratio of parent to daughter cells in newly formed rocks and particular rock sample
Fossils: found in sedimentary rocks made from layers of sand and mud
Layers of sedimentary rocks indicate the geologic time intervals
Many fossil provide evidence of extinct species, species are dynamic, the species living
on earth have changed, extinction has occurred throughout earth’s history not only
during catastrophic events
Old life is found in deep layers,
Transitional Forms:
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