This is a quick and effective way to get across to students different ways new populations can emerge, be reproductively separated from the parent population, and eventually evolve into a new species. This process, technically called Allopatry or Allopatric Speciation, is the basis for genetic drift and "bottleneck" speciation, as well as a vivid application of the point of the Hardy-Weinberg formula - without calculations!

Preparation:
Get two large plastic cups: one red and one blue;
red = all the mommas in the population, blue = all the poppas.
In each cup place equal numbers of green and red beads, say 50 green + 50 red (or any two colors).
Small white or beige cups (Dixie cups), one per person in the class (these are "baby" cups).
A wet sponge or big plastic (liter) bottle of water (with cap on) for dramatic "realism" + sound effects of waves crashing, or rushing river, etc.

Presentation (about 10-15 minutes)
Hand out little "baby" cups - one per student.
Take your two cups (a "mamma" cup and a "papa" cup) around to each student, ask each to quickly reach in (one hand into one cup, the other into the other cup, at the same time) and take a bead from each cup (without trying to pick a color) and place those two beads into his/her little cup. Quickly go around the room until each student has a pair of beads in his/her little cup. Each "take" means a pair of alleles received in a random "mating" from the population's "gene pool", and the cups are their "babies".

Ask everyone with two green beads (alleles) to raise a hand. Note where raised hands are concentrated. If no concentration, ask all with two red beads to do the same. VARIATION: Have students raise one hand for each green bead they have; that way you can get a quick sense of where all green beads are concentrated - or red beads if you ask the same for red beads.

Wherever you see a pathway to go between and separate that cluster of students with an unusually high concentration of one color or the other from the other students, start moving through that pathway.
As you go, slosh your bottle of water, making "slosh-slosh" sounds, and say "I am a river - growing larger and larger" or "I am the Colorado River - growing larger and larger." You could also say "I am a rift zone, pushing apart four continents, and making the Atlantic Ocean," or "I am building the Rocky Mountains..." or "I am the rising sea level, making lowland hills into islands." Use your creative imagination and lots of energy to dramatize whatever "barrier" you decide to build.

When done, announce that the population (students) with a high proportion of one color is now permanently separated from the parent (or other) population, and they can no longer mate with the other population. Due to a higher proportion of (green) genes, this little population has longer legs than the parent population, so they can run faster and escape predators, so they survive, and over many generations evolve into a new species with typically longer legs and accompanying features. [Always fun to capitalize on some feature of those students) - e.g., tallness, or long hair, etc. - as basis for new feature to become typical of new population (and the new species it will become).] Their new gene frequencies should be distinctively different from the parent population. You can take tally of total number of green beads in each population, then the number of red beads in each population, and note the different proportions in each. If the class has studied the Hardy-Weinberg Law, be sure to point out this application (if the students don't) - or use this to illustrate Hardy-Weinberg. If you do have your students work with the Hardy-Weinberg Law, you might find the Excel Spreadsheet Simulation helpful (below).

For further discussion and clarification of speciation, especially the part played by chromosomal changes. CLICK HERE. There is also an engaging reading and worksheet on chromosomal speciation that might be helpful: The Chromosome Shuffle

If you like to have your students work with changes in gene and genotype frequencies due to selection, you may like this Excel spread sheet. Students can alter the fitnesses and genotype frequencies and see what happens. You can skip the handout information by clicking on each cell and seeing its formula on the formula bar. Students seem to be more at home with Excel than with algebra and delta q.

This spreadsheet with instructions was kindly provided by Dr. Thomas Gregg of Miami Univ. in Oxford, OH. The PDF Instructions begins like this:

John C. Bloom. Department of Computer Science, Miami University, Oxford, OH 45056
Thomas G. Gregg, Department of Zoology, Miami University, Oxford, OH 45056

The famous Hardy-Weinberg equation shows the relationship between gene frequencies and genotype frequencies in random mating populations.

(pA + qa)2 = p2 AA + 2pq Aa + q2 aa

This formula also serves as the starting point for understanding how different evolutionary forces, such as selection, drift, and migration bring about changes in gene and genotype frequencies. In this paper we are interested in the effects of selection on gene frequencies.

Here's an even more graphic simulation, freely available online .

PopGen Fishbowl: A Free Online Simulation Model of Microevolutionary Processes by Thomas C. Jones & Thomas F. Laughlin - in the February 2010 issue of The American Biology Teacher, pp. 100-101), where you will find lots of .good suggestions for using this simulation. BTW, that issue is a goldmine of articles on teaching evolution - if you have a copy, keep it handy.

This article shares a freely available online interactive simulation of natural selection, where students can change several factors, one at a time, to test the predicted effect of each one on population size and changes in gene frequency. Makes a quick-and-easy investigative study. Suggestions for classroom use are included. You can take a look at the online simulation by clicking on the URL below, and then clicking there on "Population Genetics" in the left column. For directions, click there on "More Information." Clicking on PopGen Fishbowl there will take you directly to the online simulation.

The model is available at http://faculty.etsu.edu/jonestc/Virtualecology.htm and can be run in any browser with the Java 1.41 (or higher) plug-in.

PopGen Fishbowl is an agent-based population genetics simulation. The program contains the tools to conduct virtual experiments violating all the assumptions of Hardy-Weinberg theory. You can explore the effects of:
1- Small population size (Genetic Drift)
2- Selection
3- Mutation
4- Migration
5- Non-random mating
Some basic population biology is also demonstrated such as, logistic population growth and the Allee Effect.

If you use this simulation with your class, let us know how it goes.