Unit 9 Notes
“Evolution”
Textbook Chapter 15
Objectives:
1. Students will understand how scientific theories are developed
2. Students will compare the history of life in terms of geologic history of a species
3. Students will evaluate the scientific evidence that supports the theory of evolution
4. Students will analyze the effect of natural selection on species
5. Students will understand chemical resistance as a modern example of biological evolution
Chapter 15
A. Understanding how scientific theories are developed.
1. Scientific Theories
i. A scientific theory is a concept that has been well tested, and is accepted
as an explanation to a wide range of observations.
ii. Circular flow chart:
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iii. Uses objective experimentation to predict, verify, or refute, an assertion
made by a theory.
iv. Based on the results of the experiment(s), the theory is modified.
v. Processes involved are repeated, continually testing and modifying the
theory until the theory fits all possible experimental observations.
2. Evolutionary Theory
i. All life on Earth has a common ancestor.
ii. In order to produce the immense amount of difference among all living
organisms, certain ones had to evolve into distinct species.
1. Differentiation through evolution
2. Populations of organisms developed different traits
a. Those with traits that were more beneficial to survival
were naturally selected for survival- natural selection
3. The theory of evolution through natural selection provides a
scientific explanation for the history of life on earth as depicted in
the fossil record and in the similarities evident within the diversity
of existing organisms.
3. Major contributors to Evolution- change over time
i. James Hutton and Sir Charles Lyell1. Uniformitarianism (Gradualism) - "The Present is the Key to the
Past"
a. a geological doctrine which states that current geologic
processes, occurring at the same rates observed today, in
the same manner, account for all of Earth's geological
features.
b. Assumes that geological processes are essentially
unchanged today from those of the unobservable past,
and that there have been no cataclysmic events in earth's
history.
c. As present processes are thought to explain all past events,
the Uniformitarian slogan is, "the present is the key to the
past."
d. The doctrine of Uniformitarianism was significantly
advanced by James Hutton (1726-1797) in his publication,
Theory of the Earth (1785).
e. Hutton influenced Sir Charles Lyell (1797-1875), who is
acclaimed as the father of modern geology with his work,
Principles of Geology (1830-1833, a three volume work).
f. Lyell, in turn, influenced Charles Darwin, who later wrote
The Origin of Species (1859).
g. Lyell is responsible for the general acceptance of
Uniformitarianism among geologists for the past 150 years.
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ii. Darwin1. considered the “father” of evolution
2. wrote On the Origin of Species
3. theory consisted of two main points:
a. diverse groups of animals evolve from one or a few
common ancestors
b. the mechanism by which this evolution takes place is
natural selection
c. Darwin felt evolution was a very slow process, taking place
in innumerable small steps.
4. Theory: Natural Selection
a. the process by which forms of life having traits that better
enable them to adapt to specific environmental pressures,
as predators, changes in climate, or competition for food
or mates, will tend to survive and reproduce in greater
numbers than others of their kind, thus ensuring the
perpetuation of those favorable traits in succeeding
generations
b. Variation exists regardless of organism's needs and is not
directed toward any purpose.
c. Example: the keen eyesight of a hawk and competition for
survival
iii. Lamarck1. theory of evolution stated that species change over time ( life
started out simple and became more complex)
a. occurs through use and disuse
i. if an animal often used a particular trait or
characteristic, that trait or characteristic would
become more pronounced
1. Ex. elongated neck of the giraffe
2. Ex. toes of water birds becoming webbed
ii. disuse would cause a trait to become reduced
1. Ex. small wings of penguins
b. inheritance of acquired traits
i. Evolution occurs when an organism uses a body
part in such a way that it is altered during its
lifetime and this change is then inherited by its
offspring.
ii. This theory has been disproved by the discovery of
hereditary genetics
c. Lamarck believed that evolution takes place gradually and
constantly
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i. Species start out simple and consistently move
toward complexity, or, as he termed it, closer to
perfection.
2. Theory: Acquired Characteristics
a. believed that populations of individuals were all of the
same kind (identical characteristics in all members), but
individuals were capable of transformation and modified
by the inheritance of acquired characteristics
b. Example: Giraffe’s neck
B. Basics of Evolution: Comparing the history of life in terms of geologic history of a species:
1. Common Ancestry- Species and how they have evolved over time
2. Biodiversity
i. Ecosystem Diversity and Species Diversity
1. Reproductive Isolation
a. occurs when members of different populations are no
longer able to mate successfully with each other
i. are unable physically to mate
ii. cannot produce offspring that are able to survive
2. Behavioral Isolation
a. occurs when members of a population are not “accepted”
because of their behavior or improper courtship rituals
b. Examples:
i. the flashing patterns in male and female fireflies
ii. the courtship song and dance of the lyre bird in
South Australia
3. Geographic Isolation
a. Occurs when there are physical barriers that divide a
population into two or more groups
b. Examples:
i. Rivers, mountains, dried lake beds, or man-made
barriers
4. Temporal Isolation
a. A type of isolation that prevents reproduction because of
“timing”
b. Example:
i. Bird migrations are often governed by changing of
the seasons and food availability for their young
ii. Genetic Diversity- variance in genes is limited. As the environment
changes, especially rapidly, species could become extinct.
1. Example: Dodo Bird
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3. Rate of Evolution
i. Co-evolution- the process by which two or more species evolve in
response to changes in the other
1. Example: predator-prey relationships where the prey evolves to
escape the evolving predator as the predator evolves to better
catch its prey
ii. Convergent Evolution- When evolution towards similar traits in unrelated
organisms develops
1. Different species around the world adapt to similar environments
2. Example: shark and dolphin
iii. Gradualism- species gradually changing over time due to a gradually
changing environment
iv. Punctuated Equilibrium- predicts that a lot of evolutionary change takes
place in short periods of time tied to speciation events. (section B2 above)
C. Evaluating the scientific evidence that supports the theory of evolution.
1. Fossil Record: Darwin found fossils that closely resembled living counterparts
i. Methods for determining the age of fossils
1. Relative dating gives you an estimate of the time period of an
organism based upon the rock layer in which it is found
2. Radiometric dating uses isotopes of organic elements to
determine a fairly exact age of a substance relative to the decay
of the organic elements found in a sample (usually Carbon-14)
ii. Derived Traits- New feature that had not appeared in common ancestors
iii. Ancestral Traits- More primitive traits that appeared in common
ancestors
2. Biochemistry:
i. Anatomical and chemical similarities between life forms
ii. Genetic changes that are recorded in living organisms over many
generations
iii. Examples:
1. Genetic similarities between organisms of different species
2. The process of cellular respiration shared by all eukaryotes shows
common descent from a universal common ancestor.
3. Embryologic Development: Comparison of embryos between similar species
shows closely similar traits
4. Homologous Structures:
i. Some of Darwin’s best evidence came from the comparison of the body
parts of different species
ii. features that are similar in structure but appear in different organisms
and often have different functions
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iii. Examples:
Human Horse
Cat
Bat
Bird
Whale
5. Analogous Structures:
i. structures that perform a similar function but are not similar in origin
ii. Examples:
Shark
Penguin
Dolphin
Fin
Wing
Flipper
6. Vestigial structures:
i. remnants of organs or structures that had a function in an early ancestor
ii. Example:
1. The femur of a whale
D. Analyzing the effect of natural selection on species.
1. Fitness- The measure of the ability to survive long enough to produce “successful”
offspring
i. The key is for the offspring to survive long enough to have their own
offspring
2. Adaptations- any inherited characteristic that increases and organism’s chance
of survival
i. Can be physical characteristics or behaviors
3. Mutations- new alleles form through mutations
i. Can result from mutations of genes in reproductive cells. (Changes in
other cells of an organism cannot be passed on to the next generation.)
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ii. Some variation in heritable characteristics exists within every species,
some of these characteristics give individuals an advantage over others in
surviving and reproducing, and the advantaged offspring, in turn, are
more likely than others to survive and reproduce.
4. Directional selection
i. the effect of a shift in a population’s phenotype in response to natural
selection towards a more favored phenotype from the variation within
the original population
ii. Diagram:
iii. Example: The beak length of the Galapagos finches changed over time
due to available food sources.
1. When there was a lack of insects to eat, finches with larger and
deeper beaks survived because they could crack seeds.
2. As insects became more plentiful, directional selection favored
finches with smaller and longer beaks.
5. Disruptive selection
i. Occurs when both extreme phenotypes are favored by natural selection
while the mean population is selected against by something in nature
ii. Rarest of the three types of natural selection
iii. Diagram:
iv. Example: Peppered moths in London
1. In rural areas, the peppered moths were almost all a very light
color
2. Same moths were very dark in color in industrial areas.
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3. Darker colored moths survived predators in the industrial areas by
blending in to the polluted surroundings
4. Lighter moths were seen easily by predators in industrial areas
and were eaten
5. opposite happened in the rural areas
6. Medium colored moths were easily seen in both locations and
were therefore very few of them left after disruptive selection
6. Stabilizing selection
i. Occurs when the mean phenotype is highly favored in the environment
and becomes even more dominant in the population
ii. This can lead to a lower diversity which makes species susceptible to
disease or other limiting factors
iii. Diagram:
iv. Examples: Human birth rate
1. Infants with average birth rate more likely to survive than a baby
that is too small or too large
E. Understanding chemical resistance as a modern example of biological evolution.
1. drug-resistance in medicine
2. pesticide-resistance in agriculture
i. Student Notes:
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