Evolution Review
Define/Describe the following terms:
Evolution: the process of cumulative change in the heritable characteristics of a population.
Natural Selection: determines which individuals survive and which do not based on their environment
and the compatibility of characteristics to survive.
Fitness: an individual’s ability to survive and reproduce in a given environment
Fossils: preserved remains of ancient organism
Population: group of interbreeding individuals that live in the same place and time
Gene Pool: all the genetic information present in the reproducing members of a population at a given
time.
Allele Frequency: measures the proportion of a specific variation of a trait in a population
Speciation: The formation of a new species
Gradualism: evolutionary changes are small, continuous, and slow.
Punctuated Equilibrium: evolutionary changes are relatively quick and followed by long periods of
little or no change
Cladograms: are diagrams which depict the relationships between different groups of taxa called
“clades”
Outline the process of evolution with regards to natural selection
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Begins when an overproduction of offspring occurs in a population (group of
interbreeding individuals that live in the same place and time)
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Most organisms produce far more offspring than could survive in an
environment
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Creates competition for resources (food, water, spaced, etc.) in populations
which leads to the struggle for survival
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Competition leads to adaptive behaviors/characteristics to gain/use more
resources.
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Adaptations can lead to variation within species and populations
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Variations can provide individuals with advantage or disadvantage for survival
(natural selection)
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These advantages can lead to some individuals likelihood to survive and
reproduce, which may ultimately lead to the formation of a new species
What causes variety in the offspring of populations?
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Mutations in DNA can lead to harmful or beneficial changes in organisms phenotype
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In Each generation only a few genes mutate and most have little affect on
phenotype
Sexual reproduction is more powerful source of variation through meiosis and
fertilization
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Meiosis: Random distribution of chromosomes results in each egg and sperm
having different combinations from others
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Fertilization: Combination of different genes from sperm and egg cell and only
one sperm cell can fertilize one egg cell. Leads to variation in offspring
What is meant by the survival of the fittest?
• Individuals with characteristics that are not well suited to their
environment – those with low levels of fitness – either die or
leave few offspring
• Individuals that are better suited to their environment –
adaptations that enable fitness – survive and reproduce most
successfully
Outline the process of natural selection
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Individuals w/in population overproduce offspring, which have natural variation due to
genetic differences
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Individuals with poorly adapted characteristics are less successful at gathering
resources and have lower chance of survival
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Individuals with well adapted characteristics are more successful at gathering resources
and have a higher chance of survival
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Individuals that survive have a better chance at reproducing and passing on their
genetic traits
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Over many generations the accumulations of genetic characteristics in a population
results in evolution
Describe what happens in gene pools when evolution occurs and why.
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Gene pools are relatively stable over time, however, when changes occur, evolution is
seen
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New combinations of alleles lead to new phenotypes, that can then be selected for or
against by the environment
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Alleles that are advantageous to a populations survival will be passed on and
have a higher frequency in later generations
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Alleles that are disadvantageous will not be passes on and have a lower
frequency in later generations
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Immigrations and emigrations will also have an effect on allele frequencies
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For whatever reason, when a gene pool in modified, some degree of evolution
has occurred.
Compare and contrast the ideas of gradualism and punctuated
equilibrium.
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Gradualism: changes are small, continuous, and slow
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Supporters argue that the fossil record shows a succession of small changes in
phenotypes of species indicating the process of speciation is a steady, constant process
with transitional stages between major changes.
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These adaptations occur over millions of years
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Punctuated Equilibrium: changes are relatively quick and followed by long periods of
little or no change
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Speciation happens quickly, in a response to the environment, i.e. a volcanic eruption
that destroys some species.
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Organisms then adapt, exploiting new niches made available. The rest of the time,
species live for millions of years with little or no change
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Create a Cladogram for the following organisms and features:
Organisms: Shark, Fish, Frogs, Crocodiles, Birds, Rodents, Primates
Features: Vertebrate, Bony Skeleton, Four limbs, Amniotic Egg, Eggs
w/shell, Feathers, Hair, Opposable Thumbs.
The simplified cladogram of vertebrata is now shown with synapomorphies
indicated.
What organisms have bony ribs and shoulder girdles?
Ray-finned fish, Lungfish, Amphibians, and Land Vertebrates
What is the oldest creature in this cladogram? They youngest?
Lampreys are the oldest, Land Vertebrates the youngest
What feature is shared by amphibians and land vertebrates?
Fingers and Toes
What feature did the common ancestor of lungfish and lampreys have?
Vertebrae
What creature is most closely related to land vertebrates? Lampreys?
Amphibians to land vertebrates and Sharks to lampreys
Explain why the following examples are evidence of evolution.
Fossil Record
• indicates that life on earth is constantly changing and these changes occur
over long periods of time (hundreds of thousands or millions of years)
• Fossil - preserved remains of ancient organism.
• Support the idea that life existed on earth over 500 million years ago
Artificial Selection

changes over time in domesticated animals or plants that are chosen by breeders
Homologous Structures
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Homologous structures: Structures that are similar in form but may have different
functions, found in different species
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Indicates a common ancestor
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Vestigial Structures
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Vestigial organs
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Organs of many animals are so reduced in size that they are just vestiges, or
traces, of homologous organs in other species
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These do not affect an organism’s ability to survive and reproduce
Embryonic Similarities:
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Early stages, or embryos, of animals with a backbone are very similar
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Same groups of embryonic cells develop in the same order and pattern to produce the
tissues and organs of all vertebrates