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Unit 9: Evolution
 Evolution is
 Why have organisms changed?
o Life overproduces:
o Biotic Potential:
o Examples:
 A mustard plant produces 730,000 seeds and if they all matured the plants
would cover an area 2,000 times that of the land surface of the earth in 2
years.
 An elephant only produces 6 young in their life but in 750 yrs. will result in
19,000,000 elephants if all of the young from one pair survive.
 An E. coli in optimum conditions will equal 40,000 times the weight of Earth in
48 yrs.
 Population growth is based on available resources:
o Exponential growth is

Also known as the “J” curve & usually involves r-strategists 
o Logistic growth is due to populations facing limited resources
 These are resources in

Creates a Logistics Growth Curve or “S” Curve & usually involves k-strategists


Carrying Capacity 

Mechanisms of Death:
o Starvation (outright energy deficiency)
o Malnutrition (lack of nutrients & water)
o Predation
o Parasitic disease
o Accident
o Failure to be born
o Failure to find a mate
 Ecological factors limit population growth
o A limiting factor is
1) Density-dependent limiting factors 

Examples:
 Predation
 Competition
 Parasitism and disease
2) Density-independent limiting factors 

Examples:
 Unusual weather
 Natural disasters
 Human activities
 Genetic variation in a population increases the change that some individuals will survive.
o Genetic variation leads to
o Phenotypic variation is
o Genetic variation is
 Gene pool 
 Allele combinations form when
 Allele frequencies measure genetic variation.
o Measures
o Can be calculated for each
Example 1:
Bb = 48%
BB = 16%
bb = 36%
What is the allele frequency for
B and b?
48 ÷ 2 =
24 + 16 =
24 + 36 =
B=
b=
Example 2:
o As allele frequencies and gene pools change over time, the population evolves.
 There are two general categories of variations 
1) Discretely varying traits are
2) Continuously varying traits cannot
 Variation of these types of traits is better represented in a

Usually measured with some
 Model of population Variation:
o A normal distribution for a trait graphs as a
 Highest frequency near the mean value 
 Frequencies decrease toward
o Generally found in nature when RSNFP is achieved 
o From frequency distributions you can show:
 Mean =




Median =
 Arrange data points in order of magnitude
 Take middle measurement if sample has odd # of data points
 Take midpoint between 2 middle measurements if sample is even # of data
points
Mode =
Range =
If variations are truly bell-shaped then the
 Genetic variation comes from several sources:
1) Mutation is a
o Can form a new allele
o Can be
2) Recombination forms
o Usually occurs during
o Parent’s alleles are
Crossing Over
 Early scientists proposed ideas about evolution
o Evolution is a
o A species is
 There were many important naturalists in the 18th Century that contributed to thoughts on
evolution.
o Linnaeus 
o Buffon 
o E. Darwin (Charles’ grandfather) 
o Lamarck 
 Theories of geologic change set the stage for Charles Darwin’s theory.
o There were three theories of geologic change:
 Catastrophism 

Gradualism 

Uniformitarianism 

Uniformitarianism is the
 Charles Darwin (1809 – 1882)
o made a famous voyage on the HMS Beagle – his most famous observations were
those taken at the
 Darwin observed differences among Galapagos Island species.
o Variation 
o Examples:
 Galapagos tortoises that live in areas with tall plants have long necks & legs
 Galapagos finches that live in areas with hard-shelled nuts have strong beaks
o An adaptation is a 




Species are able to
Adaptations can
If an adaptation helps an organism in its environment then it can survive and
reproduce.
If the characteristic is not good in their environment then they will either die or
leave few offspring.
 There are 2 main types of adaptations:
1) Physical Adaptations – 3 types:
a. Physiological or Chemical 
b. Mechanical:
i. Adaptive Coloration 
ii. Deceptive Markings 
iii. Aposematic Coloration 
iv. Mimicry 
c. Structural:
i. Adaptations are 
ii. May include 
2) Behavioral Adaptations 
 Darwin observed fossil and geologic evidence supporting ancient Earth.
o He found fossils of
o He found shells high up in the Andes mountains
o He saw land move from
o He then extended his observations to the evolution of organisms
 Several key insights led to Darwin’s idea for natural selection:
o Darwin noticed
o This was due to
o Artificial selection 
o Natural Selection 


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Heritability is
There is a struggle for survival due to
Darwin proposed that adaptations
 Natural selection explains how evolution can occur.
o There are 4 main principles to the theory of natural selection:
 Variation
 Overproduction
 Adaptation
 Descent with modification 
o Fitness is the

Individuals that are better suited to their environment survive and reproduce
most successfully
 Natural Selection acts on existing variations.
o Natural selection can take one of 3 paths:
1) Directional selection 
2) Stabilizing selection 
3) Disruptive selection 
 Speciation
o The isolation of populations can lead to speciation
 Speciation is the rise of two or more species from one existing species
o Populations become isolated when
This means their gene pools are separated; there is no more movement of alleles
between the populations.
 Isolated populations
 Genetic differences can
o Reproductive isolation can
 Members of different populations cannot
 This is the final step to
 Populations can become isolated in several ways:
o Behavioral Isolation
 Includes differences in
 They aren’t attracted to each other!
o Geographic Isolation
 Geographic isolation is when
 This is the cause of most speciation!
o Temporal Isolation
 This occurs when the
 Example: Plants may have different flowering times.
 Evolution through natural selection is not
o Natural selection can have
o The effects of natural selection
.
 Patterns of Evolution
o Convergent Evolution 
o Divergent evolution 
 Species can shape each other over time.
o Two or more species can evolve together through
 Evolutionary paths become
 Species evolve in response to
o Coevolution can occur in beneficial relationships
o Coevolution can occur in competitive relationships which can lead to
 Species can become
o Extinction is the
o Background extinction occurs
 Occurs at roughly the same
 Usually affect
 Caused by
of new predator or decrease in food supply)
 Mass extinctions are rare but much more intense.
o Destroys many species at a
o Thought to be caused by
o At least five mass extinctions in
 Speciation often occurs in patterns.
o Punctuated equilibrium
 A pattern of punctuated equilibrium exists in the
 Punctuated equilibrium is


Theory proposed by Eldrege and Gould in 1972
Revised Darwin’s idea that species arose through
o Adaptive Radiation
 Many species evolve from one species during
 Ancestral species diversify into
 Descendent species usually
(ex. introduction
 Other Mechanisms of Evolution
 Genetic Drift –


Changes in allele frequency and gene pool leads to changes in
Small populations are most affected

The founder effect is

The allele frequencies in the founding population may be different than
the larger population from which they came.
 Evidence for Evolution
o Fossils
 A fossil is


Fossils in older layers are
Fossils provide
o The study of geography provides evidence for evolution
 Island species most closely
 Populations can show variation from
o Embryology
 Identical larvae, different adult body forms
 Similar embryos, diverse organisms
o The study of anatomy provides evidence for evolution
 Homologous structures
 They
 Analogous structures have
 They are not
 Ancestors lived in similar environments with similar selection pressures
o Structural patterns are clue to history of a species
 Vestigial structures are

Examples  pelvis bone in whales, ostriches, wisdom teeth, tail bones are
vestigial structures
o Molecular and genetic evidence support fossil and anatomical evidence
 Two closely-related organisms will have
o Pseudogenes are
 They no longer
 Are carried along with
 Can be clues to a
o Hox genes
o Control
o Found in many organisms
o Protein comparisons or molecular fingerprinting reveals similarities among
 Evolution unites all fields of biology
o Scientists from any field
o The basic principles of evolution are