Evolution Review
Evolution: change in the traits of a species over time
Species: a group of organisms who can produce fertile offspring
Charles Darwin:
 developed the theory of evolution called Natural Selection
 Natural Selection states that:
o there is variation (differences) within populations
o some variations are favorable [favorable variations improve an organism’s ability
to function and reproduce in its own environment]
o not all young produced in each generation can survive
o individuals that survive and reproduce are those with favorable variations; these
individuals can then pass on the favorable traits to their offspring
Evidence to Support Evolution:
 DNA: by comparing the DNA sequences of two organisms or the amino acid sequences
made from the DNA, scientists can learn which organisms are related; the more DNA
two organisms have in common, the closer related they are
Using the table, compare the amino acid sequence
of the chimp and the human.
Notice that for this protein the chimp and human
have the exact same sequence.
Now compare the baboon and the human.
Notice that there are 5 differences in the sequence.
This tells you that the human is more closely
related to the chimp than the baboon.

Fossils:
o these are the remains of once living
organisms
o fossils are found in sedimentary rock
o sedimentary rocks are often layered, so
the older a fossil is the further down in
the layers it will be
o simpler life forms are found deeper in
the rock layers because they were the
first living organisms
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
Adaptations:
o anatomical, physiological, or behavioral traits that help an organism survive and
reproduce
o homologous structure: structure or characteristic with similar functions found in
different species and thought to be inherited from common ancestors
ex: humans, whales, and bats all have the same number and type of bones in the
forelimbs
o analogous structures: structures that are similar in function, but are not inherited
from a common ancestor; ex: wings of insects and wings of birds
o mimicry: an organism can copy the appearance of another organism; in one form
of mimicry, a harmless species has adaptations that result in a physical
resemblance to a harmful species; predators that avoid the harmful looking
species also avoid the similar-looking harmless species.
o camouflage: an organism can blend into the surroundings
Speciation: the evolution of a new species when the production of fertile offspring in a species is
somehow prevented; it can occur in several ways:
 Geographic Isolation: physical barriers separate members of a population so that they
can not reproduce; these barriers can be caused by changes in climate, volcanic eruptions,
or changes in sea level; the separate groups become more and more distinct and
eventually become separate species
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
Polyploids: mistakes in meiosis cause the chromosome number in individuals to change;
when a polyploidy organism mates with a normal individual, the zygotes do not develop
normally; this type of speciation is more common in plants
Gradualism: evolution that occurs over a long period of time
Punctuated equilibrium: evolution that occurs relatively quickly on the geologic time scale
(10,000 years or less)
Variations are genetic.
Types of Evolution:
 adaptive radiation: when a species is introduced to a new environment, several new
species evolve

convergent evolution: distantly related organisms evolve similar traits

directional selection: occurs when natural selection favors one of the extreme variations
of a trait.

disruptive selection: individuals with either extreme of a trait’s variation are selected for
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Phylogeny: the evolutionary history of an organism; this is used to classify organisms into
kingdoms, phyla, classes, etc.; a phylogenetic tree or cladogram shows how organisms are
related to one another and how they evolved
examples of phylogenetic trees
Behavior: anything an animal does in response to a stimulus; types of behaviors include:
 innate behaviors: inherited behaviors
 reflex: simple innate behavior that is automatic (don’t need to think about it)
 instinct: complex pattern of innate behaviors that begins when an animal recognizes a
stimulus and continues until all parts of the behavior have been completed
 territorial behavior: behavior in which animals will defend their space by driving away
others of the same species
 aggression: behavior that is used to intimidate another animal of the same species
Extinction: the disappearance of a species that occurs when the last member of the species dies;
because environments are always changing, organisms must adapt to these changes in order to
escape extinction
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