Name _____________________________________________________
Test Date ___Tue, 3/1_____
UNIT IX - EVOLUTION
I. THE THEORY OF EVOLUTION
The theory of evolution is one of the most fundamental concepts in Biology. Evolution is defined as _changes___ in a
_population of organisms_______________________ over time. The scientist considered to be the founder of
modern evolutionary theory is _Charles Darwin__________________.
A. History of Evolutionary Theory – During the 1700s, several scientists began challenging the idea
of a world in which changes did not occur. These scientists and their hypotheses were very important
to Darwin’s work.
1. Gradualism - _Geologists_______ first suggested that the planet was much _older______ than
previously thought; began to find evidence that _changes__________ were slowly, but constantly
taking place.
2. Malthus – Published an essay that had a huge impact on Darwin. Proposed that organisms _over___ - reproduce;
in other words, reproduce at a _greater_________ rate than resources can supply.
3. Lamarck
Lamarck was one of the first scientists to propose a mechanism for evolution; that is, the _changes__
in a _population__________ of organisms over _time_____. His major hypotheses included:
 Tendency Toward Perfection – Stated that organisms were continually changing in order to
_live more successfully____________.
 Use and Disuse – Changes in _size______ and/or _shape_________ of a structure in an
organism was a response to use or disuse. Structures used extensively _grew bigger____
and structures used less frequently _got smaller____.

Inheritance of _Acquired___ Traits
B. Charles Darwin (1809 – 1882)
1. Darwin’s History
Darwin’s data was collected on a 5-year journey around the world on the HMS _Beagle___.
He made observations and collected data throughout the journey. He used this data to propose a
_hypothesis__________ to explain the diversity he saw. The area that had the greatest impact on Darwin was
the _Galapagos_____ Islands due to the differences he saw in the same animals living on different islands.
2. Darwin’s Theory of Natural Selection
 Variation - Members of a population often vary greatly in their _traits________.
 Heritability - Traits are inherited from _parents_____ to _offspring_______.
 Overproduction - All species are capable of producing _more____ offspring than _environment can
support_______. Due to a lack of _food______ or other resources, many of the offspring _will not
survive_______.
 Reproductive Advantage - Organisms with favorable _traits____ tend to survive and
_reproduce_____________________; thereby leaving more descendents than other individuals
This will result in an accumulation of these traits in the _offspring____________, changing the original
_genetic________ make-up of the population.
3. Darwin’s Theory of Descent with Modification – Based on his observations and the hypotheses of other scientists
 Each living species has descended (with changes) from other species over time.
 Implies that all living things are related to one another. Ex. Common ancestor shared by tigers, panthers, and
cheetahs –look further back and you will find ancestors that these felines share with horses, dogs, and bats. If
we look back far enough, we could find the common ancestor of all living things.
 Also known as common descent.
 According to this principle, there would be a single “tree of life” for all living things. This tree of life is commonly
known as a phylogenetic tree. These can also be referred to as cladograms.
4. Darwin’s Legacy
 Did not publish his findings for years
 Alfred Wallace – formed identical _hypotheses_______ based on his research. Sent his manuscript to
Darwin, and finally Darwin was persuaded to publish his own conclusions
 Released “_Origin of Species by Means of Natural Selection” still considered one of the greatest scientific
studies ever
II. THE PRINCIPLES OF EVOLUTIONARY THEORY
A. Evolution occurs because of natural selection - a mechanism for change that occurs when organisms with
_favorable______ characteristics for a particular environment _survive____________,
_reproduce________, and pass these characteristics on to _offspring______________.
B. The ability of an organism to survive and reproduce in its environment is known as _fitness___.
C. Fitness is based on _adaptations______. An adaptation is any trait that aids in the
_survival__ and _reproduction____ of an organism. Examples of adaptations are
_thorns on a cactus, camouflage, antibiotic resistance in bacteria_________
D. As organisms _survive__ and adapt, _speciation _____ may occur. Speciation is the formation of
new species - a group of similar organisms that _breed___ with one another and produce
_fertile offspring . . . that is, babies that can make babies!
Isolating Mechanisms allow for the gene pools to become separate so they can form a new species.
Reproductive Isolation-as a new species evolves, populations become reproductively isolated
from each other.
 Behavioral Isolation-Population is capable of interbreeding, but have different
courtship rituals. EX: Eastern and Western Meadowlark

Geographic Isolation-Two populations are separated by geographic barriers and evolve where they can
no longer interbreed. EX: Abert and Kaibab squirrels of the Grand Canyon

Temporal Isolation-2 or more species reproduce at different times even though capable.
EX:Three orchids of the rain forest, release pollen only 1 day and not the same day.
E. The failure of an organism to _adapt___ to changes in its environment will ultimately lead to its
_extinction______ because of _natural selection___.
III. EVIDENCE FOR EVOLUTION
A. Fossils – Fossils are _ preserved bones and traces of organisms _
Fossils provide a record of earlier life and evidence that evolution has occurred.
Fossils also provide evidence about the earth’s climate, geography, and life forms.
Almost _90_% of Earth’s history occurred during the Precambrian Time.
B. Biogeography – Variations are seen in the same types of animals based on their _environment_____.
In addition, there are some organisms that live in very different locations but they have similar
characteristics because _ their environments are similar; for example, climate, food sources, etc .
C. Homologous Structures – Scientists use anatomical studies of different organisms for evidence of evolutionary
relationships. For example, appendages that are very similar in structure, but differ in function are known as
_homologous structures. Examples of homologous structures are arm of human, flipper of dolphin, wing of bat.
D. Vestigial Structures - A structure that is reduced in function in a living organism, but may have been used by an
ancestor is known as a _vestigial________ structure. A structure may become vestigial when an organism
changes in form or behavior. Examples are wings of ostrich, eyes on cave fish, *human appendix*_.
E. Embryology – Similarities in the structures of developing _embryo___ of different organisms are
considered to be proof of a close evolutionary relationship.
F. DNA Sequencing – Scientists use DNA studies to determine the evolutionary relationship between organisms. The
more similar the DNA, _the closer the evolutionary relationship______________
IV. MECHANISMS FOR EVOLUTION
Evolution does not occur in an individual; instead it refers to _heritable___ _changes______ that
occur in a _population____ over time. There must be mechanisms available for _genetic_______
changes to occur:
A. Mutation – A mutation is a _change in DNA____________. Although mutations are most
often _harmful___________, sometimes the resulting change in _phenotype______ may be
beneficial to an organism under certain conditions. If the change occurs in the _gametes____, this
change will be passed onto the offspring of that organism. A positive mutation that provides a survival
advantage is known as an _adaptation____.
B. Diploidy – Most organisms are diploid, which means _double set of chromosomes_______.
This allows for increased genetic variation in a population.
 Heterozygote Advantage – Seen in _sickle cell allele___ and _malaria_.
 Recombination - Leads to increased genetic variation as a result of _crossing over during prophase I of
meiosis.
C. Gene Flow – Gene flow occurs when organisms from one community migrate to another. This introduces new
_alleles into the _population which can lead to a change in the genetic make-up of the population.
D. Genetic Drift – This describes a situation in which change in a population is magnified because the population size is
very _small__. Causes of genetic drift include:
 Bottleneck effect – large portion of population _destroyed in disaster___

Founder effect – segment of population moves to new _habitat____
E. Single Gene Traits-Natural selection on single gene traits can lead to changes in allele frequencies and therefore to
evolution. EX: Color change in a lizard population
V. MACROEVOLUTION- refers to large-scale evolutionary pattern and processes that occur over long periods of time.
A. Extinction-More than 99 % of all species that have ever lived are now extinct, which means the species has died out.
Darwin proposed possible reasons with competition for resources and environmental change.
 Mass extinction has occurred several times, wiping out entire ecosystems.
 Meteorites, volcanic action, and tectonic plate movement have been blamed.
 Mass extinctions clear the way for evolution of other species.
B. Adaptive radiation-the process where a single species has evolved through
natural selection into diverse forms that live in different ways. EX: Finches and tortoises of the Galapagos Islands
C. Adaptive radiation can have an evolutionary “side effect”, producing unrelated species
that look similar to one another. This process is known as convergent evolution
and occurs in plants and animals. These organisms have analogous structures. EX: Wing/flippers/tails
D. Punctuated Equilibrium is another pattern of evolution. Unlike gradualism,
punctuated equilibrium is characterized with long periods of stability interrupted by brief periods
of rapid change. It is controversial but known that evolution does occur at different rates.
VI. Modern Evolutionary Classification-Linnaeus tried to group organisms according to biologically important characteristics,
but his system had limitations and problems.
A. Darwin’s ideas about descent with modification gave rise to the study of phylogeny, or
evolutionary relationships among organisms.
 Biologists now group organisms into categories that represent lines of evolutionary descent, or
phylogeny, not just physical similarities.
B. Cladistic Analysis-identifies and considers only those characteristics of organisms that are
evolutionary innovations-new characteristics that arise as lineages evolve over time.
 These recent characteristics are called derived characters.
C. Derived characters can be used to construct a cladogram, a diagram that shows
the evolutionary relationships among a group of organisms.
 Cladograms-are useful tools that help scientists understand how one lineage branched
from another in the course of evolution.
 Think of them as a family tree showing evolutionary relationships among a group of organisms.
D. Similarities in Genetic Material
 DNA and RNA are so similar across all forms of life, these molecules provide an excellent way of comparing
organisms at their most basic level-their genes.
 Similarities in DNA can be used to help determine classification and evolutionary relationships.
 DNA Fingerprinting using Gel Electrophoresis is a techniques that can be used to analyze DNA and determine
these evolutionary relationships.
 Gene Sequencing or reading of the DNA of organisms allow for comparison of the DNA of different organisms to
trace the history of genes over millions of years.
E. Molecular Clocks- Comparisons of DNA can also be used to mark the passage of evolutionary time.
 A model known as a molecular clock uses DNA comparison to estimate the length of time that two species
have been evolving independently.
 The molecular clock depends on a repeating process to mark time-mutation.
 Neutral (ones that cause no changes) mutations accumulate in the DNA of different species at about the same
rate.
 Comparing these sequences, with these mutations, can tell scientist how dissimilar the genes are and in turn
how long ago the two species shared a common ancestor.
VII – THE EVOLUTION OF THE CELL – THE ENDOSYMBIOTIC THEORY