Name: ____________________________
Date: ___________________
Period: _________
Unit: Evolution
Lab Activity: Natural Selection
INTRODUCTION
Charles Darwin, in his book “On the Origin of Species” (1859), presented evidence that
the driving force or mechanism for evolution is Natural Selection. It was Darwin’s thesis that
individuals of a particular species differ by small variations, that these individuals compete with
one another for resources, habitat, space, and mates, and that some individuals would prove
better adapted to acquiring these needs due to their differences. Differential reproduction of the
better adapted individuals, generation after generation, would result in gradual changes in the
species toward better-adapted individuals (evolution).
To the modern evolutionist, natural selection means differential reproduction within a
species or population. In other words, those individuals that are “best” adapted to the
environment should, on average, leave behind more offspring than the lesser-adapted ones. This
may be due to differences in lifespan (the longer an organism lives the more offspring it might
produce), mating success, ability to have offspring, or the capability to raise offspring. In other
words, the “fittest” ones are the organisms that reproduce the most viable offspring.
Today’s laboratory investigation is designed to demonstrate the modern view of natural
selection and evolution. This is a model only. Natural systems are much more complicated (and
also are much more difficult to manipulate, which makes it much more difficult to draw
conclusions).
ACTIVITY
There are two groups in this investigation: predator and prey. The following is a
description of the first group of animals, the prey species. They are the Blue Toothpick
(common), the Red Toothpick (common), the Plain Toothpick (common), and the RoundHeaded Pick (rare).
The second group in our model are the predators –YOU! Not all predators have the same
feeding adaptations. Some predators have beaks in the shape of tongs, others look like hair
clips, some have been described as spoons, and still others have beaks shaped like clothes pegs.
Before the start of today’s lab, your study area was laid out, and 310 prey toothpicks moved in to
the habitat. The prey toothpicks include: 50 blue, 50 red, 50 plain, and 10 Giant-Round- Headed
Name: ____________________________
Date: ___________________
Period: _________
picks. It will be your job as a predator to capture as many prey as possible. The more prey
you capture, the more offspring you will be able to reproduce. At the beginning of the lab the
predator population (you) will be divided equally so that 25% are tongs, 25% chip clips, 25%
clothes pins, and 25% hair pins.
The prey must be lifted with the feeding adaptation and placed into your cup (stomach).
No scraping, shoving, or using fingers are allowed! The cup cannot touch the ground! You
cannot steal “digested” prey from another predator’s cup. It IS permissible to intrude on a fellow
predator and seize its prey -- that is, if a tongs is hard at work picking up prey, a hair clip may
rush in and take the prey for itself. This may sound like a dirty trick, but organisms in nature
seldom show compassion for other organisms when food is at stake.
What is your hypothesis with regard to the outcome of the activity?
____________________________________________________
____________________________________________________
To begin, all predators stand with their backs to the study area, on the cue of the
instructor the predators may begin hunting. After about 30 seconds your instructor will tell you
to stop. Only the prey safely in your cup (stomach) will count as captures. If you are still
capturing a prey, you must drop it.
Meet in four groups according to your predator type. Count the number of prey
toothpicks your group captured. Each predator group should report on their total haul of prey so
that everyone will be able to record the data in Table 1, on the following page. Each pair of prey
remaining has 1 offspring. If a predator type does not obtain any prey, they die and may not
continue to the next generation.
You will now perform the activity again. All offspring toothpicks (use the toothpicks you
collected in the previous generation as offspring) should be randomly distributed within the
study area. This second generation will probably be somewhat different due to changes in certain
types of predators within your population. At the end of this second feeding frenzy, repeat the
steps you followed in the first hunt. Again, fill in Table 2 on the following page and then answer
the following questions in full sentences.
Name: ____________________________
Date: ___________________
QUESTIONS
1. Which predators seem the best adapted? The least adapted? Why?
2. Which prey seem to be the best adapted? The least adapted? Why?
3. Was your hypothesis supported by this experiment? Why/why not?
4. Did any predators become extinct during the experiment? If so, why?
5. How does this investigation demonstrate natural selection?
Period: _________
Name: ____________________________
Table 1: First Generation
Yellow
Date: ___________________
Green
Plain
Giant Round
Pick
100
100
10
Green
Plain
Giant Round
Pick
Period: _________
Total Surviving Prey
Tongs
Spoons
Clothes Pins
Hair Clips
Beginning Total
100
Total Captured
Total Remaining
Total Offspring
*These will be
your beginning
total for table 2
Table 2: Second Generation
Yellow
Tongs
Spoons
Clothes Pins
Hair Clips
Beginning Total
Total Captured
Total Remaining
Total Offspring
Total Surviving Prey