Evolution & Natural Selection
Evolution
• Means “change.”
• In a narrower sense referring to
organisms, means a permanent change
occurring in a species over generations.
• Can evolution be a fact?
Forms that evolution may take
• Extinction.
• Artificial selection.
• Natural Selection – Darwin/Wallace 1859.
Natural Selection
Natural Selection works with Variation.
Variation refers to:
• A very specific aspect of a physical trait, e.g. hair texture.
• occurring within a species. Must be capable of being
passed between generations.
• It is assumed to be pre-existing and immutable (in
contrast to the theory of Acquired Characteristics and
much sci-fi literature.
• Is either distributed continuously or discontinuously in a
population.
Μ = 5’ 2.6”
4’8”
5’ 7” 5’11”
Variation is subjected to Natural
and Sexual selection
In the case of natural selection, the force of
selection stems from the environment:
The environment is all-encompassing,
amounting to anything that can potentially
kill an individual from the moment it is
conceived, e.g. mom’s drug or alcohol
use, diet, etc. while pregnant.
• It is also specific to the variation under
consideration.
In the case of sexual selection the force of
selection is the mating choice of the
opposite sex.
Sexual selection acts upon (and explains)
secondary sexual characteristics.
Secondary sexual characteristics are those
physical traits which differentiate males
from females, excluding the sexual organs
(the primary sexual characteristics).
Examples of secondary sexual
characteristics
• Feathers on peacocks/peahens.
• Manes on lions.
Humans?
Outcomes of selection:
• Individual lives or dies.
• Individual mates or doesn’t
Natural selection cannot work without
failure!!!!!
What would happen to a population if all
organisms lived and mated?
Inheritance
One of the most important concepts in the theory
of natural selection is Fitness.
Definition of fitness: differential reproductive
success. Reproduction must result in viable
offspring for an individual to be deemed fit.
Famous people with 0 fitness:
W.A. Mozart., L. van Beethoven, Johannes
Brahms, George Washington, Abraham Lincoln,
Oprah Winfrey.
• People with dubious fitness prospects:
The Clintons, Anna Nicole Smith
Nadya Suleman?
Bottom line: for an individual to have an
evolutionary impact, genes must be
passed to the next generation and beyond.
Was Darwin fit?
Adaptation
• Adaptation – permanent change in a
population brought about by natural
selection.
• Not to be confused with adaptability.
• It is the net result of hundreds or
thousands of instances of selection.
Implications of Natural Selection for
Evolution
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No goals to evolution.
No progress in evolution.
It is an amoral process.
Traits that are favored are entirely
contingent upon a given environment,
hence strength or aggression are not
necessarily favorable characteristics.