Looking at Natural
Selection in Virginia
How do we explain the adaptations we see in
the organisms that inhabit Virginia today?
Objectives
The purpose of this lesson is to inform the learner of the details of Darwin's Theory of
Evolution by natural selection and evaluate real world examples. Students will practice
using their new knowledge and then be given the opportunity to apply that knowledge to
their explanations for adaptation that they see in organisms around them.
The following are Virginia Standards of Learning this lesson addresses:
BIO.4 The student will investigate and understand life functions of Archaea, Bacteria and Eukarya.
Key concepts include comparison of their metabolic activities; maintenance of homeostasis; and how
the structures and functions vary among and within the Eukarya kingdoms of protists, fungi, plants,
and animals.
BIO.7 The student will investigate and understand how populations change through time. Key
concepts include how genetic variation, reproductive strategies, and environmental pressures impact
the survival of populations; how natural selection leads to adaptations; and scientific evidence and
explanations for biological evolution
BIO.9 The student will investigate and understand dynamic equilibria within populations,
communities, and ecosystems. Key concepts include analysis of the flora, fauna, and
microorganisms of Virginia ecosystems including the Chesapeake Bay and its tributaries.
Darwin's Theory of Natural Selection
Charles Darwin published his "Origin of Species" in 1859. Within this document he showed his genius
by proposing the following ideas (theory) of how change of organisms has taken place over the long
history of the Earth:
1. Populations overproduce offspring.
2. Within populations variations exist for all behavioral, structural, and physiological
adaptations.
3. There is a struggle for survival because of limited resources available to individuals.
4. The individuals that possess adaptations that make them most fit to the environment are
more likely to survive than those not well suited to the environment.
5. Survivors reproduce and pass their successful adaptations on to their offspring.
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Darwin shunned the idea that individual organisms make changes but embraced variation existing
within the populations as the key to surviving environmental change.
Factors increasing variation
Darwin would be delighted to know what we now know about the extent of variation in populations.
Scientists now recognize that the following factors increase variation:
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Mutations: Genetic mistakes in DNA occur often during gamete formation. If DNA is
changed, the resulting proteins change, and traits never before seen in a species will appear.
Genetic Recombination: When gametes (sperm & eggs) are produced by meiosis, only
half of the parents' genetic material is packed into them. When they unite to form a zygote
(1st cell of the new individual) the result is not exactly like either parent. Each sexually
produced offspring is unique and has variation combinations that are not present in any other
individual of that species.
Migration: Genes can flow into or out of a population due to individuals of that species
coming from a different environment. Often, new traits will be injected into the population.
Modes of Natural Selection
Today scientists see three types of natural selection working on populations as environmental
changes occur. One example occurs as a trait moves toward an extreme expression. This is known
as DIRECTIONAL SELECTION.
An example of this has been the increase in giraffe's necks over the last several million years.
Darwin would say: In the giraffe population that produces more offspring than can survive
variations in neck length exist. When the times get tough, such as dry seasons in Africa, giraffes
struggle to get enough food. Those with longer necks are more likely to survive because they reach
the leaves.
Selection that works on a population so that the extremes are eliminated is STABILIZING
SELECTION.
An example of this would be the length of cottontail rabbit legs. Rabbits with shorter legs are at a
disadvantage because they are too slow to sprint from predators. Rabbits with longer legs are
disadvantaged because they cannot turn sharp corners to get away from faster predators and cannot
get under cover easily. Midsize rabbit legs are selected by the environment.
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Selection that favors the extremes of a population trait is DISRUPTIVE SELECTION.
An example of this would be the size of clams. Predators find it harder to locate smaller clams and
are unable to pry open larger clams. Predators favor clams of a medium size.
You Try to Identify the Types of Selections
Anteaters have not always had the extremely long tongues they now use. Over the last 10 million
years, their tongues have become impressively long. Which type of selection probably is working
here?
A) directional
B) stabilizing
C) disruptive
Rabbits have a temperament that allows them to sit still most of the time, but also allows them to
get up and move before a predator gets too close. Rabbits that wait too long are removed from the
gene pool. Rabbits that tend to move all the time are spotted by predators and eliminated with
ease.
A) directional
B) stabilizing
C) disruptive
Oak trees have differentiated into species that produce many sizes of acorns. If there is a
population of oak trees that has variation in acorn size, but a new squirrel population moves into the
community and tends to select the medium sized acorns.
A) directional
B) stabilizing
C) disruptive
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Part I - You Describe Your Own Examples of Selection
You will select an organism/species that is native to Virginia from a list. Research the organism's
characteristics and explain how it may have developed its outstanding structural, behavioral, or
physiological adaptations.
Choose only one adaptation that your selected organism/species has. Please do the following:
1. Format your project research in Google Slides.
2. Explain what the positive selection pressure(s) of having the trait/adaptation is/are on the
population/species of your organism.
3. Describe how Darwin would have described the adaptation's development using his 5 ideas
of evolution.
4. Identify the mode of natural selection that might be acting on (or has acted on) this
adaptation as either directional, stabilizing, or disruptive selection and explain why.
5. Include three to five (3-5) images of your organism clearly showing/illustrating the
adaptation you chose to highlight and research. AT LEAST ONE of the images MUST be in
color.
6. Construct a phylogenetic tree with 5-6 other similar organisms showing the evolutionary
history of your species.
7. Develop a tri-fold poster to display your project research for a Gallery Walk on exam day.
Grading Rubric for “Looking at Natural Selection in Virginia”
“Examples of Selection” Component
Explanation of selection pressure(s) on adaptation
Possible
Points
8
Discussion of development of adaptation based on
Darwin’s Evolution by Natural Selection
 Variation exists
2
 Overproduce
2
 Struggles for survival
2
 Natural selection
2
 Survivors reproduce
2
Phylogenetic tree including organism
10
Mechanics (spelling and use of language)
5
Organization and format of Trifold – neat, correctly
placed, images of organism
5
Mode of natural selection with support/evidence
7
Total Points
45
4
Actual
Points
Format of Trifold for “Looking at Natural Selection in Virginia”
Explanation of Positive
Selection Pressures
Name of Organism
(Scientific & Common)
Discussion of Mode
of Natural Selection
with evidence
Researcher’s Names
Adaptation in Organism
based on Darwin’s
Theory of Evolution by
Natural Selection
Description of
Organism
Phylogenetic Tree
Print a list of sources and put on BACK of trifold.
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