Modeling Natural Selection:
PRINCIPAL CONCEPT Variation is random. Selection is not.
1. Environmental pressures determine the "fitness" of a variation.
2. Traits that are selected for (are "fitter") will be passed on to the offspring.
use model to explain how various traits may increase the ability of organisms to
California State Science Content Standards:
a. Students know why natural selection acts on the phenotype rather than the genotype of an organism.
b. d. Students know variation within a species increases the likelihood that at least some members of a species will survive
under changed environmental conditions.
Different individuals in a population have different characteristics; this is __________.
Some of this variation in characteristics can be inherited by a parent’s offspring; these are ___________ ______________.
Some characteristics make some individuals better at surviving and reproducing than others. _________ refers to the ability to survive
and produce offspring which are capable of reproducing. The specific characteristics which contribute to fitness will differ in different
A characteristic that increases an individual’s fitness is an __________.
Heritable adaptive characteristics become more common in a population over many generations. This process is called evolution by
Evolution by natural selection is a gradual process that takes place over many, many generations.
Evolution by natural selection results in changes in the frequency of characteristics and alleles or genes in a population, not changes in
Which characteristics are adaptive and how a population evolves depends on what kind of environment the population is in. The same
population will evolve differently if placed in a different environment. Organisms are not evolving to some pre-ordained “perfection”
but are evolving to maximum fitness in a given environment.
Define Natural selection, struggle for existence, adaptation, fitness, survival of the fittest
Today you will model natural selection by using various utensils to capture food
Scene - On a distant planet there exists 5 species of a creature called a Woolybooger. Each Woolybooger is similar
except their mouth has variations. All woolyboogers eat beans. Some woolyboogers have a clothespin mouth. Some
woolyboogers have a tweezer mouth, some have a needle mouth . One year a new species of woolybooger was
discovered, this woolybooger was called the Spoon-Mouthed Woolybooger . Each of you will play the part of a
woolybooger on this planet. The spoon-mouth wooly booger is rare, so only one of you will get to be this type of wooly
A tray with bean seeds
1 plastic spoons
Procedure: 1.You will run through several trials. Each trial will require your woolybooger to gain at least 20 beans. If 20
beans are not acquired during the time period, your woolybooger has died.
2. If a woolyberger gain 60 beans –it will have a offspring.
Start with 1 minute on the clock. Then reduce the time to 45 seconds, then 30 seconds, then 15 seconds.
(When a woolybooger dies, the student can play the offspring of the surviving woolyboogers. Can have a new utensil for
Represent your data in a visual.
1. What happens to animals that cannot compete as well with other animals in the wild?
2. Can you think of any real-life examples of the woolybooger, where one species has a definite advantage over another?
3. Sometimes animals that are introduced into an area that they never lived in before, out-compete and endanger resident
species, why do you think this happens?
4. If only one species is considered the "fittest", why do we still have so many variations among species. Why do some
birds have very long pointy beaks, while other birds have short flat beaks?
5. How do you think diseases can affect natural selection?
Trial Clothes # of Tweeze # of Needle Knives # of Spoon # Of Offspring
# pin Beans r Bean Beans Beans
mouth Offsp s # of Offsprings Offspring
6. On the next page there is a series of pictures representing changes in a population of cacti. Pictures 1 and 2 show what
happened when a deer came to eat, picture 3 shows the cacti a few weeks later (notice the flowers on the right-hand cactus), and
picture 4 shows the situation a few months later.
Recall that the three conditions listed below are necessary for natural selection to take place.
a Variation in characteristics within the population: In picture 1, what is the main difference between the cactus on the left
and the cactus on the right?
b.Differences in survival and reproduction, fitness: Why would a deer be more likely to eat the cactus on the left than the
cactus on the right?
c. What effect does the deer's behavior have on the survival and reproduction of these two types of cactus?
d. Heritability of characteristics from parent to offspring: The difference between the cacti is a heritable characteristic (see
e. Do you think that evolution by natural selection is occurring in this cactus population? Explain why or why not.