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Name: ________________________________________________ Date: ___________ Period: ______
Speciation Activity
Purpose: To observe the mechanisms involved in the development of a new species.
1. Your teacher will randomly divide you into groups of 3-5 students.
Group Members:
2. Your group will be isolated on an island (lab table) that has a unique environment. Please
summarize a description for your environment below.
Environment Description:
3. As a group you must select and write down all phenotype characteristics that exist in your group
that may improve your group’s survival on your island. Don’t forget to include clothing to
represent body coloration. Remember you are limited to phenotypes that are in your group
only!!! (for example: long hair may help with insulation; green shirt may help blend into a
tropical rain forest, etc.)
Phenotypes that will increase survival:
4. Imagine that your group has been able to reproduce for 500+ generations (assume no
mutations occurred). Describe the typical member of your population. Remember that each
generation should have improved its ability to survive in your environment.
Physical Description:
5. Now assume that many small mutations occurred over the next 500+ generations. If a mutation
improves survival in your environment, it will be passed through future generations.
List a minimum of 10 visible mutations that would improve survival for your species:
6. Draw a picture of a typical member of your population following the 1000+ generations of
mutations and natural selection that have occurred in this exercise.
Picture after 1000+ generations:
7. Compare your island population to the other populations that have developed in this exercise.
How are they all similar?
What are some of the major differences?
8. Do you think any of the populations in the class could represent a new species? Explain.
9. Describe what would happen if a disease wiped out all but 20 people in your large population.
How would this affect future generations? What is this called?
10. Migration can increase genetic variation when new individuals enter a population. Pretend one
of the other populations from the class joined up with yours in the very beginning, before the
species became too different. Explain why this would be beneficial.
Defining speciation
Speciation is a lineage-splitting event that produces two
or more separate species. Imagine that you are looking
at a tip of the tree of life that constitutes a species of
fruit fly. Move down the phylogeny to where your fruit
fly twig is connected to the rest of the tree. That
branching point, and every other branching point on the
tree, is a speciation event. At that point genetic changes
resulted in two separate fruit fly lineages, where
previously there had just been one lineage. But why and
how did it happen?
The branching points on this partial Drosophila phylogenetic tree represent long past speciation
events. Here is one scenario that exemplifies how speciation can happen:
The scene: a population of wild fruit flies
minding its own business on several bunches of
rotting bananas, cheerfully laying their eggs in
the mushy fruit...
Disaster strikes: A hurricane washes the
bananas and the immature fruit flies they
contain out to sea. The banana bunch
eventually washes up on an island off the coast
of the mainland. The fruit flies mature and
emerge from their slimy nursery onto the
lonely island. The two portions of the
population, mainland and island, are now too
far apart for gene flow to unite them. At this
point, speciation has not occurred — any fruit
flies that got back to the mainland could mate and produce healthy offspring with the
mainland flies.
The populations diverge: Ecological
conditions are slightly different on the island,
and the island population evolves under
different selective pressures and experiences
different random events than the mainland
population does. Morphology, food preferences,
and courtship displays change over the course
of many generations of natural selection.
So we meet again: When another storm
reintroduces the island flies to the mainland,
they will not readily mate with the mainland
flies since they've evolved different courtship
behaviors. The few that do mate with the
mainland flies, produce inviable eggs because
of other genetic differences between the two
populations. The lineage has split now that genes cannot flow between the populations.