What evolution is not
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Organisms become better
Man represents the apex in evolution
Humans descended from apes
Only a theory
Only the strongest survive
It has an end purpose in mind
1. Species produce more offspring
than survive
• Thomas Malthus believed
that there was an
overproduction of young
• Resources would not be able
to keep up with the
population growth.
• Famine and misery would
follow
• Darwin extended Malthus’
idea to include all organisms
Species produce more offspring than survive
Malthus
• Believed that this was God’s
way of keeping people from
being lazy.
• The lower class would have
to “pick themselves up by
their bootstraps” and
compete to survive
George Wallace and C. Darwin
• There was no ulterior
motivation or social classes
in nature.
• Organisms have biological
desires to survive.
2. Individuals of a species possess different genetic
traits, which help to compete for limited resources
• The different traits do
not lead to perfection.
• They have to be good
enough to get by.
• Look around, no one is
perfect.
3. Organisms that don’t survive, don’t
pass on their traits
3. Advantageous adaptations will survive
Feathers=
Adaptation
An adaptation is a feature
produced by natural selection for
its current function.
– it must be genetically
encoded—since natural
selection cannot act on traits
that don’t get passed on to
offspring.
– the trait must actually perform
that task.
– it must increase the fitness of
the organisms that have it
– did they evolve for insulation or
flight?
4. Most fit organisms survive and pass
on traits to offspring
Natural Selection
• Is mindless and mechanistic
• Selects for whatever variation is available
• Organisms do not “try”, “want” or “need” to adapt.
• Is not random.
• A mutation may be random,
• But nature acts in a specific way.
Natural Selection
• The change in the genetic frequency by
selective pressure
Types of Selection
• Directional selection - one trait is being favored and
the other is being eliminated so the population shifts
toward one trait
• Stabilizing selection - range of a trait is narrowed
• Disruptive selection - traits diverge toward the two
extremes
No species lives in isolation
• Ecological niche - describes either the role played by
a species in a biological community or the total set of
environmental factors that determine a species
distribution
– Generalist - has a broad niche (rat)
– Specialist - has a narrow niche (panda)
– Indicator species – sensitive to environmental
change ( lichen)
– Keystone species – provides ecosystem stability
(American alligator)
– Non-native invasive species (European starling)
Competitive Exclusion
• Gause proposed the competitive exclusion principle
which states that no two species can occupy the
same ecological niche at the same time. The one
that is more efficient at using resources will exclude
the other.
• Resource partitioning - species co-exist in a habitat
by utilizing different parts of a single resource.
Example: Birds eat insects during the day and bats
eat insects at night.
Resource Partitioning
All species live within limits
• Law of limiting factors: The factor in the shortest supply relative to its
demand will limit its growth
• Range of Tolerance: abiotic factor (light, nutrients, moisture)
• Plants: N for terrestrial, P for aquatic
Range of tolerance
Genetic Engineering
• Excise a gene with
the desired trait
• Insert the gene into
the host cell’s
genome
• The host organism
has the new trait
– Bt corn
Factors that influence evolution
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Mutations
Genetic drift
Genetic migration
Natural selection
Population size
Non-random mating