Natural Selection
Natural Selection
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“Survival of the Fittest”
Selection for traits that are most successful in current
environment
A constant process – environments change and therefore so do
factors that determine success
Common descent with
Modification
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Darwin proposed that
organisms descend from
common ancestors and
change with time,
diverging from the original
common form
This causes the evolution
of new species
Darwin’s 5 points of natural
Selection
1.
2.
3.
4.
5.
6.
Overpopulation
Competition
Variation
Survival of the Fittest
New Species
**Do Not Copy**
1. Overpopulation
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Organisms tend to produce
many offspring – more than
the environment can
support
Organisms will reproduce
until something stops them
(usually food)
2. Competition
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Because of overpopulation, individuals compete with one another
over limited resources  food, water, shelter, mates
Competition occurs both within and between species
3. Variation
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Individuals of a population vary in their traits and characteristics
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This variation is passed on to offspring.
4. Survival of the Fittest
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Individuals with
advantageous genetic
traits are better
adapted to their
environment
This increases their
chance of survival
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This is called
survival of the
fittest
5. New Species
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New species results by
inheritance of trait(s), on
genes, that give them
another advantage over
others
New species evolve!
Speciation
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Where one species evolves into one or more other species
Also called ADAPTIVE RADIATION
Adaptation
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An inheritable characteristic that provides an
advantage for survival and reproduction.
Adaptations can be:
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Structural – a part the organism has to help it survive
Ex: Speed, camouflage, claws, quills, etc.
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Physiological – a metabolic or chemical adaptation to help it
survive
Ex: ability to maintain internal temperature; use less water for
photosynthesis; produce a poison
Behavioral – something the organism does to help it survive
Ex: Migration; solitary vs. herds; flying in formation
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Examples of natural
Selection
1.
2.
3.
4.
Darwin’s finches
Peppered moth
Antibiotic resistant
bacteria
Pesticide resistant
mosquitoes
**Do not copy!
Populations
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Alleles exist with a certain frequency in populations of organisms
The available genes and alleles in a population are called the “gene pool”
Allele: one of two or more alternative forms of a gene that arise by mutation
and are found at the same place on a chromosome.
Mutation
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Changes in the structure of genes introduce new alleles to populations and
disrupt equilibrium
Not all mutations are good, many are fatal
This is the source of all new alleles
Selection
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Preference for a particular allele will increase its frequency in a population
over generations
Selection can happen in three different ways
Natural selection Acts on a
Population in 3 ways:
1.
If the environment favours the average of the distribution, the selection is
called stabilizing selection
Natural selection Acts on a
Population in 3 ways:
2. If the environment
favours one extreme,
the selection is
directional
Natural selection Acts on a
Population in 3 ways:
1.
If the environment favours both extremes, the selection is disruptive
If there’s time…
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Mutations: The Science of Survival
https://www.youtube.com/watch?v=qVmusHZtQms (Darwin & Natural
Selection)
20:00 to 29:29 (part 3?)
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