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EVOLUTION – CHANGE OVER TIME
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NATURAL SELECTION - INDIVIDUALS BETTER ADAPTED TO THE ENVIRONMENT
ARE ABLE TO SURVIVE & REPRODUCE.
– A.K.A. “SURVIVAL OF THE FITTEST”
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POPULATION – GROUP OF INDIVIDUALS OF SAME SPECIES THAT INTERBREED
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GENE POOL – COMMON GROUP OF ALL GENES PRESENT IN A POPULATION
2 special processes can assist with change in these populations:
Mutations change in DNA sequence in the population
Genetic Recombination (Sexual Reproduction).
Allows for new combinations of alleles and gene shuffling.
Genetic Drift may change populations through “random” changes of allele frequency.
A normal distribution of a population, based on average size.
Stabilizing selection causes a move
toward a middle, or stable, condition.
Disruptive Selection occurs when those
individuals in the middle are less fit than
those on the extreme ends.
Directional Selection occurs when a
specific trait on one side of the spectrum
or the other is selected for.
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Founder Effect: a cause of genetic drift attributable to colonization by a limited number of
individuals from a parent population (example – if you pull 10 colored balls from a trash can, and
you only pull out red ones, even through other colors are there, you end up with a new population
with only the red trait)
Gene Flow: genetic exchange due to the migration of fertile individuals or gametes between
populations (reduces differences between populations) (in human circles, think of the joining of
families).
Nonrandom mating: inbreeding and assortive mating (both shift frequencies of different
genotypes) – selective breeding for a trait we desire) – big, red apples, or heavy beef.
Natural Selection: differential success in reproduction; only form of microevolution that adapts a
population to its environment
How natural selection microevolution works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00
resistant
Generation 2: 0.96 not resistant
0.04
resistant
Generation 3: 0.76 not resistant
0.24
resistant
Sexual Selection – mate selection based on Bling
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Generation 4: 0.12 not resistant
0.88
resistant
Sexual dimorphism: secondary sex characteristic distinction (males and females look different to
attract members of the opposite sex).
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Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism
(ie – the bling pays off  )
THE FORMATION OF NEW SPECIES
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AS NEW SPECIES EVOLVE, POPULATIONS BECOME REPRODUCTIVELY ISOLATED
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REPRODUCTIVE ISOLATION – MEMBERS OF 2 POPULATIONS CANNOT INTERBREED
& PRODUCE FERTILE OFFSPRING.
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BEHAVIORAL ISOLATION- CAPABLE OF BREEDING BUT HAVE DIFFERENCES IN
COURTSHIP RITUALS (EX. MEADOWLARKS)
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GEOGRAPHICAL ISOLATION – SEPARATED BY GEOGRAPHIC BARRIERS LIKE
RIVERS, MOUNTAINS, OR BODIES OF WATER (EX. SQUIRREL)
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TEMPORAL ISOLATION – 2 OR MORE SPECIES REPRODUCE AT DIFFERENT TIMES.
SPECIATION IN THE GALAPAGOS FINCHES OCCURRED BY:
An example of adaptive radiation –
these species all diverged from a
common ancestor (founder species)
FOUNDING OF A NEW POPULATION,
• GEOGRAPHIC ISOLATION which led to -- REPRODUCTIVE ISOLATION and
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• CHANGES IN THE NEW POPULATION’S GENE POOL due to COMPETITION.
Evidence for Evolution
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Fossil Record: Fossil Record provides evidence that living things have evolved. Fossils show the
history of life on earth and how different groups of organisms have changed over time
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Geographic Distribution of Living Species: Separation by a large body of water, or land, that does
not allow species to come back into contact with each other for continued gene flow.
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Homologous Body Structures
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Similarities in Embryology
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Relative dating says the newest
rocks will have the youngest fossils.
As the rocks are deeper in the earth,
they will have older fossils from
farther back in Earth’s history.
Absolute age will utilize various
measures of radioactive decay of
materials, including Carbon, to
determine the actual age of fossils.
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Early Atmosphere – the beginnings of Earth
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Earth was Hot!!
Little or no oxygen
Gasses in atmosphere:
 Hydrogen cyanide (poison to you!)
 Hydrogen sulfide
 Carbon dioxide
 Carbon monoxide
 Nitrogen
 water
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Where did Oxygen come from?
Some of that oxygen was generated by photosynthetic cyanobacteria
Some came from the chemical separation of water molecules into oxygen and hydrogen.
Oxygen drove some life forms to extinction
Others evolved ways of using oxygen for respiration
Miller and Urey’s
Experiment
 Passed sparks
through a mixture of
hydrogen methane
ammonia and water
 This produced
amino acids – the
building blocks of
life
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Where did Oxygen come from?
Some of that oxygen was generated by photosynthetic cyanobacteria
Some came from the chemical separation of water molecules into oxygen and hydrogen.
Oxygen drove some life forms to extinction
Others evolved ways of using oxygen for respiration
So how does the formation of amino acids make cells?
Formation of microspheres
 Large organic molecules can sometimes form tiny proteinoid microspheres
 Store and release energy, selectively permeable membranes, may have acquired more
characteristics of living cells
Endosymbiotic theory
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eukaryotic cells arose
from living
communities formed
by prokaryotic
organisms
Ancient prokaryotes
entered primitive
eukaryotic cells and
remained there as
organelles