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Evolution
Evolution:
change over time;
the process by
which modern
organisms have
descended from
ancient organisms
Scientific Theory:
a well supported
testable
explanation of
phenomena that
have occurred in
the natural world
Charles Darwin:
 born in England
1809, on the same
day as Abraham
Lincoln
 traveled around the
world on H.M.S.
Beagle
Charles Darwin:
Made numerous
observations and
collected evidence
that led him to
propose a
hypothesis about
the way life
changes over
time, the theory of
evolution
Darwin’s Observations:
 Patterns of diversity: he observed such a large
variation of species in similar environments
 EX: He saw rabbits in England but not in Australia even
though the environment was similar
Living Organisms and Fossils:
 He observed that fossils of ancient organisms resembled
organisms that were still alive.
 Others looked unlike anything he had ever seen
Galapagos islands:
many islands close
together with very
different climates.
Darwin observed
that the
characteristics of
many animals and
plants varied
noticeably among
the different
islands
Ex: Tortoises
 The differences = to the environments
in which the respective tortoises live,
and the types of food they eat.
 domed tortoises tend to live in the
moist high-lands and take their food
from grasses and low-lying shrubs.
 saddle-backed tortoises live in arid
regions and feed on plants that are
mostly above their head. The arched
shell permits them to stretch their
heads high, giving them a longer
vertical reach.
On the Origin of Species:
Darwin’s book
published in 1859
that summarized
all his findings
from his trip
around the world.
Artificial Selection:
 nature provides the
variation and
humans select
those variations
that they find
useful.
 ** Used to improve
crops and livestock
 Selective breeding
transformed teosinte's few
fruitcases (left) into modern
corn's rows of exposed kernels
(right).
Natural Selection:
 Over time, results in
changes in the
inherited
characteristics of a
population and
increase fitness
(ability of an
individual to survive
and reproduce in its
specific environment)
of a species.
Darwin's illustrations of beak variation
in the finches of the Galápagos Islands,
 which hold 13 closely
related species that
differ most markedly
in the shape of their
beaks.
 The beak of each
species is suited to its
preferred food,
suggesting that beak
shapes evolved by
natural selection.
Adaptation:
 an inherited characteristic that increases an organism’s
chance of survival.
Struggle for Existence:
members of each species compete regularly to
obtain food, living space and other necessities of
life.
In general, organisms produce more offspring
than limited resources can support, and
organisms therefore compete for survival.
Descent with modification:
 natural selection
produces organisms
that have different
structures,
 establish different
niches
 or occupy different
habitats.
 This causes today’s
species to look different
from their ancestors.
Common Descent: all living
organisms are related to one
another
Evidence of Evolution:
Fossil record
Evidence of Evolution:
Homologous
Body Structures:
structures that
have different
mature forms but
develop from
same embryonic
tissues
(Wings and legs
all descended from
the fish fin)
Evidence of Evolution:
Vestigial Organs:
remnants of organs that
have no function now
Evidence of Evolution:
Similarities
in
Embryology
Evolution of Populations:
 A population is a group of individuals of the same
species that interbreed and share a common group of
genes
Gene pool all the genes, including all the different alleles, that are
present in a population
Relative frequency of an allelethe number of
times that the
allele occurs in a
gene pool,
compared with the
number of times
other alleles for
the same gene
occur. Expressed
as a percentage
Evolution any change in the relative frequency of alleles in a
population
Single-gene traits –
any traits controlled by one gene.
(EX: widow’s peak in humans)
natural selection on single-gene traits can lead
to changes in allele frequencies and thus to
evolution
Polygenic Traits-
any traits
controlled by 2 or
more genes
(EX: eye color and
skin color)
Natural selection
can affect the distributions
of phenotypes in any of
three ways: directional
selection, stabilizing
selection or disruptive
selection.
Directional selection:
 when individuals at one end of the curve have higher
fitness than individuals in the middle or at the other end.
(EX: seed size and bird beak size)
Stabilizing selection:
 when individuals near the center of the curve have
higher fitness than individuals at either end of the curve.
(EX: weight of human infants at birth)
Disruptive selection:
 when individuals at the upper and lower ends of the
curve have higher fitness than individuals near the
middle (EX: seed size and bird beak size)
Genetic Drift:
 in a small population, individuals that carry a particular
allele may leave more descendents than other
individuals, just by chance.
 Over time, a series of chance occurrences of this type
can cause an allele to become common in a population
Name 3 chance events that could
cause genetic drift to occur?
Founder effect:
 genetic drift due to the migration of a small subgroup of
a population.
 (EX: Fruit Flies migrating from mainland to different
Hawaiian Islands)
Hardy-Weinberg Equilibrium:
 allele frequencies in a
population will remain
constant unless one or
more factors cause
those frequencies to
change.
 Also called genetic
equilibrium
 Five conditions are
required to maintain
genetic equilibrium
from generation to
generation
 Random mating
 Large population
 No movement into or
out of the population
 No mutation
 No natural selection
Speciation: formation of new species
Reproductive
isolation: when
the members of 2
population cannot
interbreed and
produce fertile
offspring
Behavioral isolation:
when two
populations are
capable of
interbreeding but
have differences in
courtship rituals or
other reproductive
strategies that
involve behavior.
Geographic isolation:
when 2
populations are
separated by
geographic
barriers such as
rivers, mountains,
or bodies of water.
Temporal isolation when 2 or more species reproduce at different times