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The Theory of Natural Selection
Biology I
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I. Early Biology
• Scientists knew
that organisms had
changed
• Fossil evidence
• Age of the Earth
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Lamarck
• Changes from simple
to complex
• Organisms want to
adapt or change
• Acquired
characteristics were
inherited (passed on)
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Lamarck
• Later disproved
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II. Darwin
• At 21, took a job as
a naturalist on the
HMS Beagle
• Collected
specimens, took
notes of different
organisms
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His voyage:
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II. Darwin
• Sailed to Galapagos
Islands
• All new species, but
similar to those found
elsewhere
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• Finches most famous
• Had slightly different beaks from island to island
• Differed by their diet
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II. Darwin
• Darwin 22 years
developing theory of
natural selection
• Pressured into
publishing by
Wallace
• Published On the
Origin of Species by
Natural Selection
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III. Natural Selection
4 Requirements
•1. Variation exist
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2. Differential
Reproduction
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3. Heredity
Best suited survive and
reproduce
4. Lots of Time
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1. Variation
• Variations exist
– Color, size, speed, etc.
• Variations are genetically
linked
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2. Differential Reproduction
• Organisms produce more
offspring than can survive
– creates competition and
Survival of the Fittest =
Only the best are going to
survive
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Heredity
• Beneficial variations
survive, pass traits to
offspring
• Passed through DNA
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Natural Selection
• Over time variations
become more frequent
in population
• Results in population
being different than
ancestors
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Evolution
Evolution is the change in a population over time
Natural Selection - Remember the Giraffe?
How did it get the long neck?
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Evidence of Change
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Fossil Record
Anatomy & Physiology
Embryology
Biochemistry
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Fossils
• Remains or traces of living
organisms
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Physiology
Mimicry-An adaptation
• Enables one species to resemble another
species.
• Ex.-harmless species looks like a harmful
one, good tasting vs. bad tasting.
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Camouflage-An adaptation
• A species blends in with its environment to
avoid predators.
• Ex.- peppered moth,
leaf frog
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Anatomy- Homologous
Structures
• Common evolutionary origin.
Similar in arrangement or function
or both.
• Example: forelimbs of a whale, a
crocodile and a bird wing.
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Anatomy- Analogous Structures
• No common evolutionary origin,
but similar in function.
• Wings of a bat and wings of a
butterfly.
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Anatomy- Vestigial Structures
• No function now but was probably useful to
an ancestor.
• Ex. A whale has leg bones, a snake has leg
bones
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Embryology
• Earliest stage of growth and development
• Embryos of a fish, a chicken, a pig, a cow, a
rabbit, and a human are almost identical.
• They all have gill slits and a tail.
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Biochemistry
• Comparisons of DNA and RNA
• Now monera (prokaryotes) is divided into
two separate kingdoms based on their
biochemistry.
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V. Mechanisms of Evolution
• Genetic Drift
• Gene Flow
• Artificial Selection
• Natural Selection
Sexual Selection
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Genetic Drift
• Change in allele
frequency by
CHANCE
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GENE FLOW
• Bottleneck effect
• Founders effect
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Gene Flow
• Change in allele frequency as a
result of MIGRATION
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Sources of Variation
• GENE FLOW moves genes among
populations
• SEXUAL REPRODUCTION
introduces new gene combinations
• Random MUTATIONS in DNA
lead to the formation of new
alleles (sound familiar?)
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Mutations
• Can be beneficial, neutral, or
harmful for the organism
• Only mutations in gametes are
inherited by offspring
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Bell:
• What is the difference between Analagous
structures, Homologous Structures, and
Vestigial Structures?
• What are the 4 requirements of Natural
Selection?
AGENDA
•Intro to Classification
•Natural Selection Today
•Antibiotics
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