Transcript Theories of Evolution

Theories for Evolution
Mr. Young
Evolution
• The process of change within a living
system over a period of time
• Genotype changes vs. Phenotype
changes
• Micro vs. Macro Evolution
• Many different scientists have proposed
theories about this process….…
Microevolution:
Small-scale evolutionary changes,
usually on the molecular level, that
occur over the span of a few
generations and can therefore be
detected in living populations.
Macroevolution:
Large scale evolutionary changes,
speciation events, that may require
many hundreds of generations and
are usually only detectable in the
fossil record
Natural Selection:
The differential reproductive success
of certain phenotypes within a given
environment
“Survival of the Fittest”
Jean Lamarck
1744-1829
“Acquired Traits”
• Theory of use and disuse
• If an organ is used , it becomes stronger
and better developed
• If an organ is not used, it becomes weaker
and withers away
Lamarck
• An organism acquires traits from its experience
(not genes) and those traits are passed down, or
inherited by their offspring
• Example: Lamarck believed that giraffes
stretched their necks to reach food. Their
offspring and later generations inherited the
resulting long necks.
To Lamarck this means…
• If you have a nose job, your kids will
inherit the new nose!
• In real life, what nose will your kids get?
(the old one or the new one?)
• Answer: the old one!
Is this logical?
• What determines that traits are passed to
their children?
– DNA
• If you change your appearance, will your
children inherit the new appearance
– No, because your DNA did not change
Natural Selection
• Environmental
Selection
• Role of the
Environment
• Acquired traits????
(Lamarck)
Who’s Your Daddy?
• Charles Darwin
– Theory-descent w/ modification
– Theory-natural selection-main principles:
Charles Darwin
1809 - 1882
• A naturalist (studied and preserved
biological specimens that he collected)
• 5 year voyage around the world aboard
the HMS Beagle
Charles Darwin
• Theory of evolution by natural selection
– Nature will select the organisms that have
variations that allow them to better survive
(survival of the fittest)
– Descent by Modification
– Darwin collected different species that were
very similar and hypothesized that they
shared a common ancestor
insects
finches
Darwin’s Book:
Origin of Species by Natural Selection
• Described his theory of evolution
• Caused a lot of controversy and angered
the church
• The church initially believed that evolution
is a sin against God
• Before Darwin died, the church accepted
his theory and he was buried in a famous
church in England
Charles Darwin
• Darwin’s theories are accepted today as
the most accurate explanation for
evolution
Darwin explains why giraffes have
longer necks than their ancestors
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Overproduction – too many giraffes
Struggle or compete for food
Variation in length of neck exists naturally
Longer neck…reach food...survive
Longer necked giraffes survive and
reproduce to eventually originate a new
species of giraffes
Hugo De Vries
• Added the concept that mutations in DNA
are what cause organisms to change or
have variations
• Evolution is changes in
DNA that is then inherited
(microevolution)
Variations in organisms
• Each species has organisms
with varying characteristics
for example:
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some are taller
some have bigger feet
some run faster
some have better vision
some smell better
Struggle for existence
• Overproduction of a species causes
competition for resources to survive
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food
water
shelter
space
Survival of the fittest by means of
natural selection
• Variations may give certain organisms
advantages to survive, while other
organisms died
• Nature selects those organisms that will
die or survive
Evidence for Darwin's theory
• Fossil record
• Biogeography
• Comparative
Anatomy
–Embryology
–Biochemistry
Evidence for Evolution
Homologous structures
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Similar shape
Different function
Shared origin
Example: arms of human, wings of bats,
wings of penguins, arms of alligators
• Divergent evolution
Evidence for Evolution
Analogous structures
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Different shape
Similar function
Different origins
Example: wings of a humming bird and
wings of a moth, both allow the organism
to hover
• Convergent evolution
Vestigial Structures
• A structure that had a use in an ancestor
but has no use in a particular organism
• Examples:
– Appendix in humans
– Tail bones in humans… we have no tails
– Tiny leg bones in snakes…they have no legs
– Wings in penguins…they do not fly
– Nipples on boys…they do not produce milk
Embryology
• The study of an organism from creation to
birth
• Embryos have
– tails that vanish into their spines
– gill slits, like fish to breath that vanish into
ears
– coats of hair that fall off at birth
Embryos go through stages of
heart development
• 2 chambers like fish hearts
• 3 chambers like reptiles
• 4 chambers like birds and mammals
Adaptations
• A trait that increases an organisms
chances of survival
What forces cause evolution?
1. Mutation
2. Migration (gene
flow)
3. Genetic drift
– Random events
– Small populations
4. Non-random mating
5. Natural selection-4
types;
Types of natural selection
• Stabilizing
• Directional
• Disruptive
– Aka
diversifying
• sexual
Natural Selection?
• What leads to these
changes?
– Random mutations
• Organisms w/ shorter
generation times have
higher mutation rates &
so evolve quicker than
animals w/ longer
generation times
• Examples:
• Industrial Revolution
vs. Peppered Moth
Natural selection results from
Selection Pressures
• those aspects of the environment that can have a
notable impact on the reproduction of members of a
particular species over evolutionary time.
• adaptations
Defense Mechanism
• Different ways for organisms to defend
themselves
• Example: thorns on rose bush
Mimicry
• Copying the appearance of another, more
dangerous specie
• Example, the fat bumble bees do not sting,
but they copy the yellow/black appearance
of thin bumble bees that do sting
Camouflage
• The ability of an organism to blend into
their environment
• Example, fish have pale bottoms and dark
tops
• Frogs are shades of green
Let’s play name that
adaptation!!!