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Evolution
Charles Darwin (English Scientist )
• Ideas 1st to be published
• HMS Beagle
– South America and South Pacific 5 year journey
– Organism diversity led to curiosity about relations
– Galapagos
• Species-unique but similar
• Led to idea of change over time (spent 22 years
studying)
• Ideas supported by fossil evidence
Galapagos Unique Adaptations
• Galapagos finch
– Beak feed on Cacti
• Galapagos Tortoises
– Largest in body size and shape
• Galapagos marine iguanas
– Eat algae on ocean bottom (unusual food for
reptile)
– Large Claws-slippery rocks
Charles Darwin
• Base on Thomas Malthus idea “Human
population grows faster than Earth’s food
supply” Darwin realized organisms:
– Struggle to survive
– Struggle for food
– Compete for space
– Escape predators
– Find mates
– Find shelter
Darwin and pigeons
• Breed and watched survival
• Traits--vary depending on size and inheritance
• Artificial Selection-breed organisms with
specific traits
Darwin and Natural Selection
• Mechanism for change in population
• Organisms with certain variations, survive,
reproduce, and pass their variations to next
generation.
• Organisms without variations less likely to
survive and reproduce.
Natural selection
gradual process by which biological traits
become either more or less common in a
population as a function of the effect of
inherited traits on the differential
reproductive success of organisms
interacting with their environment.
Darwin-how species change over time
• Organism produce more organisms than can
survive (fish millions of eggs)
• Individuals in a population have variations
(different color, size, speed)
• Individuals with useful variations survive and
pass traits (speed)
• Overtime-offspring with certain variations
make up most of population and may look
different from ancestors.
Darwin
Determined that species did not arise
independently; rather species are
descendants of other species.
Alfred Russell Wallace
• Studied in Indonesia and Amazon River
• Introduced Theory of Evolution
• “Useful variations will tend to increase, unuseful or hurtful variations to diminish”
• Some qualities of an individual may allow it to
outlive another w/o qualities; pass qualities to
offspring.
Lamarck’s Model
• Jean Baptiste de Lemarck
• Individuals change due to environmental
influences; organisms adapt based on
individual needs
• Acquired changes passed to offspring
• “Use and disuse”- stronger is used; weaker if
not used; overtime modified due to use or
disuse; disuse may disappear.
Relationship of work by Lamarck,
Wallace and Darwin
• Darwin refuted Lamarck’s hypothesis that
individuals change to meet needs due to
environmental stress and that these acquired
characteristics
• Wallace work overshadowed by Darwin; Now
some celebrate Wallace more
– Jointed presented to scientific community
Visualizing Evolution
Evolution difficult to observe
– Short scale of human life
– Contradictory to faith
– Interpretations of data
Evidence for Evolution
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Structural
Physiological
Fossils
Anatomy
Embryology
Biochemistry
Structural adaptations
• Special structures and body parts
• Mimicry
• Camouflage
Structural Adaptations-develop over
millions of years
• Size of teeth
• Claws
• fingers
Mimicry—Structural adaptations that enables one
species to resemble another.
• Batesian- a species without any special defense
mechanism mimics another species that predators
avoid. (Same warning signs –coloring, pattern—no
defenses—chemicals, spines)
• Mullerian- more than one species with similar defense
mechanisms all have the same coloration (Same
warning signs and same defenses)
Mullarian Mimicry-avoid being eaten;
pass on genes
Camouflage
• Adaptation-blend in with surroundings
Darwin’s idea of natural selection
ex Mole Rat
• Current animals probably resemble African
rock rats
• Ancestors avoided predators-size of teeth
and claws
• Ancestors survived passes variations to
offspring
• Over time-modern mole rat—blindness
evolved b/c no survival advantage.
Physiological Adaptations-(some rapid)
• Changes in metabolic process
– Bacteria that resist antibiotics
– Insects and weeds resistant to chemicals that kill
them.
Fossils
• Record of early life and
evolutionary history
• Still incomplete recordjigsaw puzzle
• As become more
complete, sequence of
evolution more clear
Anatomy
• Homologous
Structuresstructural
features with a
common
evolutionary
origin
• Similar
arrangement or
function or both
Anatomy
• Analogous (aka “convergent”) Structures-Do
not have common evolutionary (evolved
independently) origin but similar in function
Anatomy
• Vestigial Structure-Body structure with no
function in present day organism (ancestor’s
may have used)
– Eyes on blind mole-rat and cave fish
– Forelimbs of ostrich
Embryo
• Earliest stage of growth and development of
plants and animals.
• Similarities among young embryos suggest
evolution from a distant, common ancestor.
Biochemistry
• DNA and RNA comparisons
• Determine evolutionary relationships b/w
species
• 1970s RNA and DNA nucleotide sequencing to
construct evolutionary diagrams.
Mechanism for Genetics and Evolution
• Genetics used to explain variation among
individuals of a population
• Studies of the complex behavior of genes in
populations-population genetics
• Populations, not individuals evolve.
Natural Selection acts on range of
phenotypes in populations
Gene Pool
All the alleles of the populations genes.
Allele frequencyPercentage of any specific allele in a gene pool.
Genetic equilibrium
Population in which the frequency of alleles
remains the same over generations
• Affect small populations
• Observed in small human populations that
have been isolated
• Can result in an increase of an allele in a small
population (Amish)
Genetic Drift
Alteration of allelic
frequencies by
chance events
Disrupts Equilibrium
Genetic Equilibrium Disturbances
• Gene Flow-transport of genes by migrating
individuals
– Leaves-genes lost from gene pool
– Enter-genes added to gene pool
• Mutations, genetic drift and gene flow may
significantly affect the evolution of small and
isolated gene pools (island)
• Natural selection most significant factor to
change a gene pool.
Natural Selection acts on variations
• Variations can be inherited and they are
controlled by alleles
• Allelic frequencies in a pop’s gene pool will
change over generations due to natural
selection.
• Three types of natural selection: Stabilizing,
directional and distruptive
Stabilizing selection
• Natural selection that favors average
individuals in a population
Directional Selection
• Natural selection favors one of the extreme
variations of the trait
Disruptive selection
• Individuals with either extreme of a trait’s
variation.
Speciation
• When members of similar populations no
longer interbreed to produce fertile offspring
within natural environment.
– Geographic isolation
– Reproductive isolation
– Polyploid
Geographic isolation
• Physical barrier divides population
– Prevents interbreeding between 2 groups
• Founders Effect