Transcript Natural selection

Natural selection
Charles Darwin
• Born February 12, 1809 Shrewsbury England
• Medical School (1825-1827)
– Darwin is 16 Years Old
• Cambridge (1827-1831) Clergyman
• Naturalist of H.M.S. Beagle
• Beagle Departs from Plymouth, England
on December 27, 1831
– Darwin is 22 Years Old
H.M.S. Beagle
Route of the H.M.S. BEAGLE
timeline
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January 1832 Santiago, Cape Verde Islands “Seashells”
April 1832 Rio de Janeiro, Brazil “Entomological Specimens”
August 1832 Patagonia Coastline “Useless Junk (Fossils)”
March 1833 Falkland Island, Port Louis “Comparing Fossils”
September 1835 Galapagos Islands, “Discovering Diversity”
October 1836 Falmouth England, “Journey Ends” 4Y9M5D
March 1837 London Zoo “Discovery of Darwin’s Finches”
November 1859 Published “Origin of the Species”
1930’s-1940’s Evolutionary Synthesis “Mendel and Darwin”
Theory of
Natural Selection
1.
Organisms produce more offspring than can survive.
2.
In any given population, variations exist.
3.
Individuals with certain “useful” or beneficial variations
survive and pass on their variations to the next
generation.
4.
Over time, offspring with “beneficial” variations will
make up most of the population.
Natural Selection
Darwin used his collections and
observations to identify a mechanism for
change in populations.
Darwin called this mechanism:
NATURAL SELECTION
Natural Selection
Science’s “best guess” on how
populations change over
time.
Natural Selection is based on the
following scientific evidence.
Structural Adaptations
Physiological Adaptations
Fossils
Anatomy
Embryology
Biochemistry
Structural
Adaptations
Structural adaptations • Defensive Adaptations
• Large Teeth and Claws, Speed and agility,
are changes in an
chemical
organism’s appearance
Structural Adaptations usually
develop over a long period of
time
• Protective Adaptations
• Camouflage, Mimicry, Speed, Chemical,
Quills, Spines
• Specialized
• Height, Strength, “Specialized Anatomy”
Physiological
Adaptations
Changes in an organism’s
metabolic processes.
Can occur over a relatively short
period of time.
• Examples
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Bacteria
Pesticides
Herbicides
Symbiotic Relationships (Clown
Fish and Sea Anemone)
FOSSILS
FOSSIL EVIDENCE:
• Provide record of early life
• Show how changes occurred
within most populations and
species.
• FOSSIL SHORT
COMINGS
– Incomplete for many
species
– Inferences [However, DNA can
support these inferences]
ANATOMY
CONVERGENT EVOLUTION
Organisms share same
function, but not the same
form, come from different
ancestral lineages.
• Analogous Structures
– Similar structural functions but do
not share a common evolutionary
origin.
• Similar in function but not
arrangement
– Insects vs. Birds
ANATOMY
DIVERGENT EVOLUTION
Species that were once similar
• Homologous Structures
– Structural features with a common
evolutionary origin
• Can be similar in arrangement and
function.
– Forelimbs of human, cat, whale, bat
• Vestigial Structure
– Body structure in a present day
organism that no longer serves its
original purpose.
• Feature is still inherited, although it no
longer serves it’s purpose.
– Eye balls present in blind cave
salamander
Embryology
• Early Embryonic development, all embryo’s have a tail and
pharyngeal pouches.
Biochemistry
• Organisms share same
biochemical molecules
– DNA, ATP, ENZYMES, AMINO
ACID SEQUENCE
• Organisms that are
biochemical similar have fewer
differences in their amino acid
sequence and are believed to
be more closely related or
share a common ancestor.
• Phylogeny: Construction of
“family trees” using DNA and
RNA
THE EVIDENCE
• Scientist use:
– Adaptations
• Structural
• Physiological
– Fossils
– Anatomy
• Micro and Macro
– Embryology
– Biochemistry
• DNA, RNA, Amino Acids
Applying Natural Selection
• SPECIATION: Process in which a new species arises from a formerly interbreeding
population.
– Cause
• Geographic Isolation
• Reproductive Isolation
– Rate
• Fast—Punctuated Equilibrium
» Periods of speciation occurs quickly within a long period of genetic equilibrium.
• Slow—Gradualism
» Species originate through a gradual change of adaptations.
Applying Natural Selection
• Populations, Not Individuals, Evolve
– Variations arise from mutations
– Alleles represent the genetic variation in a population
– The Gene Pool is the all of the different alleles in a given
population.
– The percentage of any one allele in the gene pool is called the
Allelic Frequency.
– If the frequency of an allele remains constant we refer to that as
Genetic Equilibrium.
Applying Natural Selection:
Directional Selection
Natural Selection Favors One
Extreme Variation of a Trait
Example:
Birds with varying sizes of beaks,
after a drought, the large beak birds
have selective advantage
Applying Natural Selection:
Disruptive Selection
Individuals with either extreme trait
are selected for.
Example:
Tourists in the desert like
to pick up a souvenir from
their travels, they pick up
the medium spine cactus.
Leaving the “homelier”
low spine and avoiding
the “prickly” high spine
cactus, both of which have
the selective advantage.
Applying Natural Selection:
Stabilizing Selection
Natural Selection Favors average
individuals in a population.
Example:
Birth weight in humans is
highly variable, however, a
child that is of average
weight has a higher
chance of being born and
of good health, as to
mature and reproduce.
Nature selects against the
extreme phenotypes.
Natural Selection is currently the best
theory scientists have to explain the
vast diversity of life on Earth and how
populations change over time. In
science, nothing can ever be proven as
fact, there are no facts in science, only
“best guesses”. These best guesses
are based on current, verifiable, and
testable evidence. We call a collection
of evidence that fails to disprove a
hypothesis—a theory. In fact, science
can only be used to disprove not prove
anything.