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Lecture 7

BIOLOGY 1M03 Lecture Notes - Lecture 7: Allele Frequency, Evolution Of Biological Complexity, Genetic CorrelationPremium


Department
Biology
Course Code
BIOLOGY 1M03
Professor
Jon Stone
Lecture
7

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BIOLOGY 1M03 - Lecture 7- Evolution by Natural Selection (Continued)
Misconceptions on Evolution:
Natural selection acts on individuals, but evolutionary change occurs only in
the characteristics of a population.
The individuals themselves do not change or evolve in their own
lifetime.
Acclimation is not adaptation. Acclimation occurs when an individual's
phenotype changes in response to changes in the environment, but the
individual's genotype remains fixed, so the changes are not passed onto
offspring.
In contrast, adaptation occurs when the allele frequencies in a
population change in response to natural selection.
Evolution is not goal-directed. It is simply favoring individuals that happen to
be better adapted to the environment at the time. Adaptations do not occur
because organisms want or need them.
Evolution is not progressive, meaning it does not produce better or more
complex organisms; scientifically, there is no such thing as a lower or higher
organism.
Organisms do not act for the good of the species, meaning individuals with
self-sacrificing alleles die and do not produce offspring (except possibly when
kin-selection operates). Individuals with selfish alleles survive and produce
more offspring.
Limitations of Natural Selection:
Adaptation is an imperfect process. Some traits are nonadaptive, and the
adaptations that organisms have are constrained in a variety of important
ways. These include genetic constraints, fitness trade-offs, and historical
constraints.
Lack of genetic variation can constraint evolution because natural
selection can only work on existing variation in a population.
Fitness trade-offs are compromises between traits, in terms of how
those traits are adapted for the environment.
Because selection acts on many traits at once, an adaptation
may be a compromise.
When traits evolve from previously existing traits, adaptations are
subject to historical constraints.
Histories for evolutionary novelties are difficult to assess.
Not all traits are adaptive, and even adaptive traits are constrained by genetic
and historical factors.
Adaptation is used to refer to patterns (e.g. traits) and processes (e.g. how
those traits are affected).
For example, human male nipples exist because they for in embryos
before gender-determining hormones start directing male organ
development.
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