The Love Game
Natural Selection
Standard B-5: The student will demonstrate an understanding of biological
evolution and the diversity of life
Standard B-5.1: Summarize the process of natural selection
Key Concepts:
Biological evolution: microevolution, macroevolution
Natural selection
Overproduction of offspring
Variation: inherited traits
Adaptation: fitness, survival of the fittest
1. Exploration
1. Give the students a pre-macmod with several questions on the topic of
biological evolution and natural selection. These will be completed
individually so that the instructor can assess the each student’s knowledge
of the subject prior to the exercise.
2. Introduce the students to some examples of animals that have taken an
interesting evolutionary turn.
3. Introduce the topic of biological evolution and biodiversity as well as some
of the key terms / names that are associated with the topic: Charles
Darwin (“On the origin of species”), natural selection, competition,
predation, and resource limitation etc. It should be stressed that multiple
factors drive the evolution of a species: genetic mutation, environmental
factors: abiotic (i.e., avg. annual rainfall), and biotic (i.e., predation).
4. Natural selection field activity – The Love Game.
5. Another review on natural selection, evolution. The hypotheses generated
will be displayed.
6. Data will be analyzed a presented graphically to the class. The students
will be asked (classroom discussion) to interpret the data and whether this
supported of refuted their hypotheses
7. The post-MacMod will be handed out. This could be a take-home
assignment if time runs short.
Field Exercise “The Love Game”– Teacher’s Copy
Objective:
The goal of this exercise is to familiarize the students with the effects of sexual
selection, genetic variability, and environmental changes on a population. To
accomplish this, students will act out roles as members of an animal species.
Males and females will be given randomly assigned “traits” that represent some
level of fitness within the population. They will then act out several trials
(seasons) under differing levels of biotic and abiotic stress in order to examine
how these factors can cause shifts in the ratio of genotypes and phenotypes
within a population.
Materials Needed
1. Party hats
2. Sunglasses
3. Beaded necklaces
4. Love cards: assigned number of offspring for an individual trait
5. Container to hold ornament assignments for random drawing
6. Cape (predator)
7. Computer equipped with Microsoft Excel or a similar spreadsheet
program capable of producing graphical output.
Students will be divided into groups of males and females. Males will draw
random cards to determine which ornament they will display
Males:
There are four male genotypes / phenotypes possible at the beginning of this
exercise:
1. No ornaments = least desirable
2. Hat = moderately desirable
3. Sunglasses = moderately desirable
4. Hat + sunglasses = most desirable
Females:
There are two female genotypes / phenotypes possible at the beginning of this
exercise:
1. No necklace = low fecundity
2. Necklace = high fecundity
At the beginning of each season (trial), the females will be separated from the
males and secretly told what “traits” are most desirable. They will then go into
their habitat (classroom, gymnasium, courtyard, etc.) to wait for the males to
come in. When the males go into the habitat, they will approach the females and
attempt to “mate”. The females will either accept or reject the mating offer. If the
female accepts the male, she will give him her “love card” which displays the
appropriate number of offspring assigned to the male’s ornaments.
Each male may be paired with up to two females during the course of one
season. This will replicate the difficulty of males finding receptive females in
nature. Each season will last approximately 3 minutes (this will vary with class
size, but it should be short enough that students will need to be quick in making
their choices and weigh the costs and benefits of waiting for a more desirable
male or accepting one that is less acceptable so that at least some offspring are
ensured). As in nature, the ultimate goal here is to produce offspring to carry on
your genetic material – it does the students no good to be too picky in their mate
selection.
Number of offspring:
1. Male w/ two ornaments + Female w/ ornament = 5 offspring
2. Male w/ two ornaments + Female w/ no ornament = 4 offspring
3. Male w/ one ornament + Female w/ ornament = 4 offspring
4. Male w/ one ornament + Female w/ no ornament = 3 offspring
5. Male w/ no ornament + Female w/ one ornament = 2 offspring
6. Male w/ no ornament + Female w/ no ornaments = 1 offspring
Once the male students have found a female, she will accompany him for the
rest of the season, so she is unable to give another male her love card. This will
replicate the territoriality of some males in the wild and make it easier to count
offspring at the end of the season. At the end of each season, the students will
gather with their mates at a common location so the instructor or a delegated
data recorder can record the pairings and number of offspring. These data will be
entered into Excel so that population trends can be analyzed for the next class
period.
The number of seasons will vary depending on the time available and the
number of selection factors (predators, disease, natural disasters) introduced by
the teacher. The idea is to allow students to perform a couple seasons with only
sexual selection first. In this way, they can see the results of one trait being
dominant and occurring more often in the offspring. Then, different selection
pressures can be added (a new predator or disease that preys almost exclusively
on males with hats and noisemakers) to show the students how other factors can
change definition of “fitness” within a population.
A few rules and logistical items:
1. Once a male and female “mate”, they must remain together for the
duration of that season. There is to be no fighting between the males.
2. Each male is only allowed two females per season.
3. The number of offspring for the entire season will be tallied; 50% will be
considered to be males, 50% will be considered females. For simplicity,
we are only tracking the traits of males in this population. Female offspring
will only be used to track the total population size.
4. For simplicity, the number of breeding-age adults will be kept constant
throughout the exercise.
5. The method for determining the number of offspring possessing each
genotype / phenotype is as follows:
(Xa / T) * M
where Xa = number of offspring conceived by genotype a
T = the total number of offspring conceived that season
M = the number of males conceived that season