Download Multiple mechanisms of evolution Name(s): Jesse Lasky Title of

Multiple mechanisms of evolution
Name(s): Jesse Lasky
Title of lesson: Multiple mechanisms of evolution
Date of lesson: 4/9/09
Length of lesson: 70-100 minutes, depending on the students
Description of the class:
Name of course:
Grade level: 7th grade
Honors or regular: Regular
Source of the lesson:
The natural selection portion of the lesson is modeled after an activity
mentioned to me by Timothy Keitt, the rest is my creation.
1.
Overview
This lesson is geared toward getting students to learn that there are multiple
mechanisms of evolution, that natural selection is but one of them, and that determining
which mechanism led to current patterns is often difficult to ascertain.
II. Performance or learner outcomes
Students will be able to describe three mechanisms of evolution. They will describe the
forces driving each mechanism. They will describe possible outcomes of each mechanism.
III. Resources, materials and supplies needed
1.
Copious amounts of Skittles and M&Ms. Approximately 1 bag of Skittles for each
group, and 1 large bag of M&Ms for each group (see below).
2.
2 bowls will be needed for each group.
3.
A notebook to record data
IV. Supplementary materials, handouts. (Also address any safety issues
Concerning equipment used)
N/A
V. Safety Issues
Students should wash their hands beforehand, because they will certainly end up eating
some of these. Make sure to buy plain M&Ms in case students are allergic to peanuts.
Make sure any students allergic to chocolate or who cannot eat sugar are not eating
M&Ms.
Five-E Organization
Teacher Does
Probing Questions
Student Does
Will probably come up with an
Define “evolution” in your
Engage:
example of natural selection.
review the definition of evolution, ask
own words.
Something affects the survival
groups to each come up with a specific
Describe a way in which an
or reproduction of individuals
scenario for some potential evolutionary organism might evolve. How
with a certain trait, and those
change.
could a bag of M&Ms evolve
most successful pass on their
(change over time)?
genes to future generations.
Approx. Time__5__mins
The other mechanisms
discussed below, or sexual
selection (e.g. peacocks), may
also be described.
Student should state that genes
Students should be asked the
Evaluation(Decision Point
are the basis of heredity, and
above questions. Different
Assessment):
they should describe some
proposed mechanisms of
mechanism capable of changing
evolution that students come
a population's gene frequencies.
up with should be written on
Heredity may also occur
the board. Later we will
through epigenetic
address their accuracy.
mechanisms, although genes
are the predominate carriers of
information determining
phenotypes passed from one
generation to another.
Explore:
Divide the students into groups,
with at least two groups for each rule of
evolutionary change. Ask each group to
make predictions about how the
composition of their population of
M&Ms will change over time. Ask
them to predict how consist this
outcome would be across many
populations (or student groups). Ask
students to predict which rule of change
will result in the greatest change in
M&M composition. See the end for
instructions for the simulations with
different “rules” (i.e. mechanisms of
evolution). If time is available, you may
wish to have each group do a simulation
of each rule of evolutionary change.
During prediction making: will
the M&Ms become
homogenous (all of one
color)? Which mechanism
will result in the fastest
change?
During simulation:Are the
M&M populations evolving?
Why or why not? Is the
amount of M&Ms of each
color changing over time?
Why? Why do the proportions
not stay constant? How is this
similar to actual organisms in
nature?
When I taught this, I did it in a
45 minute period, and there was
not enough time to both go over
the directions for all rules of
evolution AND run the
simulations. The students need
reminded of the rules multiple
times (at least with a group of
students who were average at
following directions). As a
result the students only carried
out the natural selection rule,
and they largely were able to
identify the mechanism for
change and the likely outcome
of such a force on the
proportion of M&Ms of
different colors. We were not
able to get to the part of
comparing the different rules.
Approx. Time__10__mins
Evaluation(Decision Point
Assessment):
Natural selection students (rule
#1) should state that their
preference for certain colors of
M&Ms reduced the number of
these M&Ms, and the other
colors persisted.. Neutral
genetic drift students (rule #2)
should state that there are
random fluctuations in the
proportions of M&M colors
because of the random deaths.
Students in bottleneck groups
(rule #3) should also state that
the change is random, but they
should recognize that there will
likely be dramatic differences
between the original and final
population of M&Ms.
Pass among groups asking the
questions about the
mechanism behind evolution
in each group. Ask students to
explain why their predictions
fit or do not fit with the
observed data (outcome).
All students should be able to
identify the mechanisms behind
their evolutionary change, and
they should describe the
changes in the population in
relation to those mechanisms.
Explain:
Students present their evolved (i.e.
changed) populations to the rest of
the class. Ask students whether
the candy evolved over time and
why (how does what they saw fit
with the definition of evolution as
change in a populations gene
frequencies over time)? Give them
a representative, unevolved,
“normal,” straight out of the
original M&M bag population to
hold up in comparison to their
final, post-evolution population.
They describe the rule of
evolution and why it created the
observed final population. They
should give an example to the
class of the changes in frequency
of a few of the colors from start to
finish. They give a hypothetical
example in nature.
Approx. Time___5__mins
Evaluation(Decision Point
Assessment)
As groups are presenting, ask
each group to listen and think
about the following questions:
What is similar about the
evolution of each group? (you
can put these on the overhead
projector, or have groups
stand up at the front and hold
them up) What is different?
Does the outcome of some of
the mechanisms (or “rules”) of
evolution produce more
consistent results than other
mechanisms? Why?
After presentations are done,
have groups discuss these
questions for ~2 minutes and
have a few groups share with
the class.
Students state that the natural
selection experiments should
provide more consistent results
because the mechanism is based
on species traits, whereas it is
random for the other groups.
Depending on the results,
students may observe that the
bottleneck results have the most
variability and the least
predictability.
Have student groups describe
the cause and effect of each
kind of evolution. If time
permits have individual
students repeat this orally or
in a journal or quiz format.
Students should describe the
mechanisms underlying each
group’s evolutionary change,
and link that cause to the
observed effect.
Extend / Elaborate:
Further discussion, either as a group or
back in their original pairs or small
groups. Students may make pie graphs
showing original composition of the
group and final composition, or they
may make graphs with multiple lines
showing the change in each M&M color
frequency over time. Students may
come up with their own animals and
write a story saying how they could
evolve in each of the 3 ways we saw.
Approx. Time__5___mins
Evaluation(Decision Point
Assessment):
Does the color of the M&M
make a difference in the no
Skittle populations?
Does natural selection give
M&Ms some trait they
“need”? Did M&Ms “try” to
adapt?
What if only purple M&Ms
were safe from predators,
would M&Ms persist? (NO,
there are NO purple M&Ms,
unless they propose humans
can create them). But this gets
at whether students understand
that selection cannot create
different kinds of phenotypes,
it can only act on already
existing phenotypes.
In natural populations, where
does the variation in M&M
come from?
How is it transmitted to future
generations?
If I showed you a population
of M&Ms that had no blues,
what would you conclude
about the evolution of these
M&Ms?
Discuss these questions and
determine if students are
adding misconceived
mechanisms to evolution.
Students often think that natural
selection acts and gives species
traits they “need,” and that
individuals “try” to adapt.
Natural selection only acts on
existing variability in
populations, resulting in
differential fitness of
phenotypes.
Students should state that these
alternative mechanisms of
evolution can create similar
patterns. If they do not realize
this, advocate an opposing
mechanism to the one they first
proposed for the above question
about “If you found a
population of only red, yellow
...” Get them to defend their
position, or they may give in
and identify alternative
explanations for observed
patterns Additionally, present
them with evidence from their
simulations, where different
rules may have resulted in
similar outcomes.
Evaluate:
Students should be able to design studies
that would allow them to compare the
competing hypotheses that explain how
traits arise. Have each group come up
with an example organismal trait to
study, and what kinds of data they could
collect in order to rule out or to support
each hypothesis.
Approx. Time___5__mins
For any given information they
propose to collect, ask them
which specific hypotheses it
either supports or refutes. Ask
them how many hypotheses
information can support or
refute (multiple).
How can we show that one of
these rules is or is not acting
on a population?
Students should design
experiments or suggest data
collection that would test the
individual steps that must occur
in each of these mechanisms of
evolution.
Some students may deny the
existence of evolution. For the
scope of this lesson, ask them if
they saw evolution in the M&M
populations and why or why
not? (If the frequencies of
M&M colors changed over
time, this is evolution). Ask the
students if they agree that
something similar could happen
in nature, and to come up with
a hypothetical example. Many
anti-evolutionists acknowledge
micro-evolutionary change
(small changes), but deny the
common ancestry of all species
(large changes between
species). This nuance is
beyond the scope of this lesson,
although it is worth pointing
out to students that scientists
have found single genes (like
the M&M colors) that can have
dramatic impacts on
development (e.g. determining
whether something has 4 or 6
legs).
STUDENT DIRECTIONS
FOR ALL GROUPS: ANYONE NOT FOLLOWING DIRECTIONS IS ELIMINATED AND
CANNOT EAT ANYTHING
We are studying populations of M&Ms. Sometimes many M&Ms are killed by disasters all at
once.
Evolutionary Rule #1
1. You will receive M&Ms. Students put 2/3 of the M&Ms in an empty ziplock bag marked
"Offspring," and the other 1/3 in a bowl or dish.
2. Students must go through 3 generations
3. Each student picks their favorite color of M&M. They may only eat that color.
Generation
A. At each generation the group records the number of M&Ms of each color.
B. Then each group member takes turns selecting one M&M and eating it Students go around 2
times doing this so that each student selects twice each generation.
C. Once all students have gone, record the number of surviving M&Ms of each color, and add
one M&M child of the same color from the offspring bag for every pair of the parent M&Ms in
the population. If only one M&M remains of a color, it has no offspring.
3. In the last generation, the students should write down how many M&M children would be
added to the population, but you do not need to add them to the dish.
Evolutionary rule #2
1. You will receive M&Ms. Students put 2/3 of the M&Ms in an empty ziplock bag marked
"Offspring," and the other 1/3 in a bowl or dish.
2. Students must go through 3 generations
Generation
A. At each generation the group records the number of M&Ms of each color.
B. Each student closes their eyes and selects one M&M and eats it.
C. Once all students have gone, record the number of surviving M&Ms of each color, and add
one M&M child of the same color from the offspring bag for every pair of the parent M&Ms in
the population. If only one M&M remains of a color, it has no offspring.
3. In the last generation, the students should write down how many M&M children would be
added to the population, but you do not need to add them to the dish.
Evolutionary rule #3
1. You will receive M&Ms. Students put 2/3 of the M&Ms in an empty ziplock bag marked
"Offspring," and the other 1/3 in a bowl or dish.
2. At the first generation, each student closes their eyes and picks 7 M&Ms and eats them. It is as
if a hurricane, flood, fire, or other natural disaster came along and wiped out almost all of the
M&Ms.
3. Once all students have gone, record the number of surviving M&Ms of each color, and add one
M&M child of the same color from the offspring bag for every pair of the parent M&Ms in the
population. If only one M&M remains of a color, it has no offspring.
4. In the second generation, the students record the number of each color of M&Ms in the
population, and then add one M&Ms child of the same color for each parent M&Ms in the
population.
5. Finally in the third generation, the students record the number of each color of M&Ms in the
population, and then add one M&Ms child of the same color for each parent M&Ms in the
population.
Data sheet
Generation
Beginning of
generation 1
Surviving at
end of
generation 1
Beginning of
generation 2
Surviving at
end of
generation 2
Beginning of
generation 3
Surviving at
end of
generation 3
# Red
M&Ms
#Yellow
M&Ms
#Green
M&Ms
#Blue
M&Ms
#Brown
M&Ms
#Orange
M&Ms