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Evolution: descent with modification
 Genetic change over time in a common ancestor
which makes an organism more suited for an
environment
 Unifying principle of all biological sciences
 Universally accepted fact
 What factors can change DNA over time?
 DNA changes can result in organismal changes
 Phenotype vs genotype
Evolutionary Terms
 Adaptive trait-any form or function that allows an
organism to survive in its current environment
 Fitness-measure of reproduction, ability to produce
viable and fertile offspring
 Gene pool-all the genes of a population
 Allele-different forms of a gene (trait)
 Mutation-change in the DNA; the original source of
genetic variation
History of Evolutionary Thought and Ideas
 400 BC Plato, Aristole: Every object was an
imperfect copy of an ideal form; diversity of
organisms some more complex than others,
species organized by degree of complexity
 1400s Century Global exploration: discovery
of organisms never seen before
 1600s discovery of fossils; organisms that
were no longer found on earth, but they were
similar to some still alive
History of Evolutionary Thought and Ideas
 1700s Carolus Linnaeus began taxonomy of living organisms
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based on differences and similarities (binomial nomenclature)
1700s Leclerc (Count Buffon) documented with evidence
descent with modification  generation after generation, will
result in variation
1700s Erasmus Darwin (Charles’ grandfather) wrote on
common descent based on development, artificial selection,
vestigial structures
1798 Malthus, population size correlates with famine, disease,
war
1830 Lyell, “Principle’s of Geology” by studying the earth’s
layers, natural catastrophes, determined that the earth was not
6000 years old, but millions
History of Evolutionary
Thought and Ideas
 1700s careful studies of differences
and similarities between organisms,
Lamarck’s Inheritance of
Acquired Characteristics, giraffe’s
neck and the “stretching”
hypothesis; genotypes are inheritednot necessarily phenotypes
 1700s Cuvier founded paleontology
and catastrophism after a
natural disaster or extinction new
species from surrounding areas
repopulated area; used to explain the
variation of fossils in different
stratum layers
History of Evolutionary
Thought and Ideas
 1831 Charles Darwin
5 year voyage
around the world on
the HMS Beagle.
 S America and The
Galapagos islands;
collected over 200K
species, observed
massive geological
changes, stratification
of earth’s layers, read
Lyell’s Principles of
Geology
History of Evolutionary Thought and Ideas
 Found fossil of glyptodonts-
ancestors of current day
armadillo
 Could the armadillo come
from this?
 A change would require
millions of years; earth
must be olderLyell
suggested the earth was
much older than 6000 years
and the observed changes
occurred gradually over long
periods of time
History of Evolutionary
Thought and Ideas
 Darwin looked at the
biogeography of organisms
 No rabbits in SA, but Patagonian
hares, same niche…different
ancestors?
 In Galapagos Islands (965 km from
mainland) tortoises with
different lengths of necks, and
finches with different sizes of
beaks, depending on island they
were located and food source
available
 Could the tortoises/finches on the
islands come from an ancestor on
the mainland?
History of Evolutionary Thought and Ideas:
Darwin
 Darwin’s Finches-
Galapagos Islands
 Depending on the island
and resources available,
nectar vs. seed size, the
birds beaks were
different, yet they were
finches
History of Evolutionary Thought and Ideas:
Darwin
 Looked at dog
breeding; wolf  dog
 Artificial Selection by
humans produced
different dog breeds.
 Could there be a
natural selection
process not driven by
humans but by
environmental factors?
Variation in
Populations
 Why is there so much species diversity?
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Yet, so many common traits?
What Factors Produce Genetic Variability
in a Population?
Crossing Over-prophase I, Meiosis
Independent assortment-metaphase I,
Meiosis
Chromosome number changesnondisjunction in Anaphase,
mitosis/meiosis
Chromosome structure changesdeletions, duplications, translocations,
inversions
Mutations-somatic vs. germ cells, silent
Fertilization-1 sperm + 1 egg
Darwin’s Theory of Natural Selection
 Through his travels to SA and Galapagos Islands,
collecting and observing different species
 By reading the works of other scientists who
presented data on geology, anatomy, competition,
population size, and artificial selection
 Darwin published “The Origin of the Species”
which contained Natural Selection as a
mechanism that drives Evolution
Natural selection:
Obs. 1) All species have great potential fertility and population size would increase
exponentially if all born reproduced successfully
Obs. 2) Populations tend to remain stable in size
Obs. 3) Environmental resources are limited
-Inference 1: Production of more individuals than
the environment can support leads to a struggle for
survival; only a fraction survive
Obs. 4) Individuals vary, no 2
individuals are exactly alike
Obs. 5) Variation is heritable
-Inference 2: Survival is not random;
those individuals with beneficial
inherited traits will leave more offspring
Differential reproductive success
-Inference 3: This differential reproduction leads to gradual change in populations;
the product of natural selection is adaptation of populations to their environment
selects
Natural Selection
drives
Evolution
is
individual phenotype
over time
change in genotype frequency
of population
Individuals do not evolve; populations do
ex. English Peppered Moth
Factors That Drive Natural Selection
 Competition for limited resources
 High reproductive rates
 Variability and adaptability of traits
 Heritability of traits
Natural Selection is Observable
 Darwin’ finches  beak depth
 Peppered moths  switch from
light to dark color
 Marine snail  thickness of
shell
 Honey creeper  beak smaller
 Bacteria  antibiotic resistance
 Cancer cells/HIV  drug
resistance
Evidence for
Evolution
 Fossils-buried remains and
mineralized impression of
organisms from the past; older
fossils  deeper sediment layers
 Transitional fossils-an organism
that shows features from 2
different lineages; intermediate
form, common ancestor
 Archaeopteryx transitional form
between reptiles and birds
 Ambulocetus  terrestrial
ancestor of whales
The Fossil Record
 Only those organisms with hard parts preserved the
best
 Have to find the fossil
 Some fossils not intact; erosion, water and earth
movement, predators
 Complete records for many lineages have been found.
Ex. Horse
The evolution of the horse
involves the gradual
development of the modern
horse from the fox-sized,
forest-dwelling
Hyracotherium.
Paleozoologists have been
able to piece together a
more complete picture of
the modern horse's
evolutionary lineage than
that of any other animal.
Evidence for Evolution
 Biogeography
 Study of the range and
distribution of organisms
on earth
 When organisms are
related, they evolved in
one region and spread to
other accessible regions
 Different organisms would
be expected when
geography separates land
masses, islands, oceans
Evidence for Evolution
 Comparative Morphology
 Study of bone structures and body
organization between different
organisms
 Looking for similar structures with
similar functions between groups
 Stem reptile forearm has
homologous structures that are
found in human, bat, porpoise,
penguin, chicken, pterosaur
 Analogous structures: bird vs. bat
vs. insect wing
Evidence for
Evolution
 Comparative Embryology
 Study of embryos and early
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development patterns between
different organisms
Early embryos (up to 6 weeks) of
humans, fish, chicken, reptile look
identical. Why?
Human embryos have gill slits,
webbed fingers/toes, tail, fur
Vestigial structures: features that
are fully developed in one group of
organisms but are reduced and
have no function in similar groups
Must have same ancient
instructions (DNA); variations in
later development due to
mutations and transposons
Evidence for Evolution
 Comparative Molecular Biology: all living organisms use the same
hereditary molecules; these molecules were present in the first
living cell and have been passed to all extant organisms
 Study differences/similarities of proteins. Many “housekeeping” enzymes
will be the same in function, but not aa sequence between organisms
 Study differences/similarities of DNA sequences. The more closely related
the DNA sequence between 2 organisms, the more closely related they are
to each other. Humans and chimps DNA are 99% identical