ORIGIN & EVOLUTION NOTES
According to current evolutionary theory, life appeared on
earth about 3.5 billion years ago. Evidence from microfossils
and radiometric dating (Carbon-14 or Potassium-40) support
this theory.
Evolution—the theory that species change over time.
Types of evolution include:
 Microevolution—change in allele frequencies within a
population
 Macroevolution—evolutionary change at the species
level or higher; that is, the formation of new species, new
genera, and so forth.
Important proponents of evolutionary theory in order of
occurrence include:
 Charles Lyell—a Scottish geologist wrote Principles of
Geology (1830). Lyell proposed that plant and animal
species had arisen, developed variations, and then became
extinct over time. He also believed that the Earth’s
physical landscape changed over a long period of time.
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 Thomas Malthus—wrote an essay called The Principles of
Population. In it, Malthus proposed that populations
outgrew their food supplies, causing competition between
organisms and a struggle for one species to survive
against another.
 Jean Baptist de Lamarck—proposed the first mechanism
for evolution called “the inheritance of acquired
characteristics”.
 Charles Darwin—naturalist on ship HMS Beagle. Ship was
chartered for a five year mapping and collecting
expedition to South America and the South Pacific.
Wrote a book called On the Origin of Species, which
proposed the mechanisms for evolution to be a process
called
natural selection.
Indirect evidence for evolution includes:

The fossil record

The geologic column or time scale—based upon the idea
that the earths layers can be dated according to what
fossils they contain, older organisms being found near
the bottom of the column and younger organisms found
nearer the top of the column. By matching rock layers
with fossils, geologists can determine the age of the
rocks, while paleontologists can determine the age of the
fossils. This is called relative dating. Includes the
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Precambrian, Paleozoic, Mesozoic and Cenozoic (most
recent) Eras


Comparative anatomy
1.
Homologous structures—forelimb bones of some
2.
Analogous structures—body parts of organisms
3.
Vestigial structures—body structure that has no
4.
Embryology—the study of how animal embryos
mammals exhibit this.
that do not have a common evolutionary origin, but
are similar in function. Examples would include
insect wings and bird wings.
function in a present day organism but was probably
useful to an ancestor.
develop; during early stages of development many
animal embryos look similar
Biochemistry—comparisons of the proteins, DNA, or RNA
of different species.
Direct evidence for evolution includes:

Pesticide resistance in insects and other organisms

Antibiotic resistance in bacteria
Processes involved in evolution include:
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Natural selection—the process by which organisms with
favorable adaptations survives, and reproduces at higher rates
than organisms with less favorable adaptations.
From all the information gathered by Darwin, two central concepts
emerged to form the basis of his theory of evolution.
 First, Darwin observed that variations within a species
were dependent on the environment. Adaptations are
genetically coded traits that occur in organisms and
enable them to be more successful in their environment.
Darwin reasoned that the importance of these
adaptations is to ensure the survival through
reproduction of that species. The organisms that lack
these adaptations will not reproduce as successfully.
 Secondly, the organisms on the Galapagos Islands had
become geographically separated from one another. This
resulted in reproductive isolation. There is no
interbreeding between organisms of the same species
that are located on different islands. For example,
finches on one island could not breed with finches of the
same species on another island. He theorized that within
a population of a species, adaptations would arise due to
reproductive isolation. The organisms would develop
adaptations to their environment over time that would
result in significant differences between the same
species on different islands.
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Types of natural selection include:
1.
2.
3.
4.
5.
Stabilizing selection—individuals with the average form
of a trait are selected.
Directional selection—individuals with one extreme form
of a trait are selected.
Disruptive selection—individuals with either extreme
form of a trait are selected.
Sexual selection—preferential choice of a mate is based
on the presence of a particular trait.
Artificial selection—intentional breeding of organisms to
produce certain traits
Extinction—of the species that have existed on the planet, more
than 99% are extinct. Mass extinctions are thought to be brought
about by some sort of catastrophe or climate change that
produces conditions too severe for most species to endure.
Extinction is thought to be a major cause of evolution.
Speciation is the evolution of a new species that occurs when
interbreeding happens, or when the production of fertile offspring
is prevented. In the physical world, natural barriers form and
cause the breakup of populations to form smaller populations.
Volcanoes, sea-level changes, and earthquakes are a few examples
of natural occurrences that affect populations. This is known as
geographic isolation. Geographic isolation prevents
interbreeding, so gene exchange will cease. So over time, each
smaller population will adapt to their new environment through the
process of natural selection.
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Eventually, this causes the gene pool of each group to become
different so that it can be concluded that there is a new species
formed.
The rate of speciation can proceed in one of two timeframes:
 Gradual evolution (gradualism)—idea that evolution
occurs a slow even rate over extremely long periods of
time
 Punctuated equilibrium—trends in the fossil record
cannot be attributed to gradual change within a lineage,
but rather to quick bursts of evolutionary change.
Patterns of evolution:
 Adaptive radiation—when diversity seems to have occurred in a
newly evolved species in a relatively short time. They also believe it
occurs when an organism colonizes a new area in which there is
another organism that is lacking in survival skills. Researchers use
the example of the finches Darwin observed on the Galapagos
Islands. He counted over a dozen different kinds of finches that he
believed evolved from a single founding species.
 Divergent evolution (adaptive radiation is one type of this)—pattern
of evolution in which species that once were similar to an ancestors
species diverge, or become increasingly distinct.
 Convergent evolution—occurs when unrelated species occupy similar
environments in different parts of the world. Because they share
similar environmental pressures, and therefore, similar pressures of
natural selection, they tend to have many of the same
characteristics.
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