Darwinian Snails: What Makes Populations Evolve? 2007

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Darwinian Snails: What Makes Populations Evolve? 2007. Part of EvoBeaker series. Produced by SimBiotic Software, 148 Grandview Ct., Ithaca, NY 14850. (617) 812-0093. Visit www.simbio.com for ordering and pricing information.

This simulation is part of the larger series EvoBeaker, which includes other computer-based activities that look at various aspects of the evolutionary process. Darwinian Snails looks at the underlying principles of natural selection using green crabs preying on periwinkle snails. The instructor and the students are given a set of assumptions and by turning these on and off, the user can then observe whether natural selection has occurred. The program is divided into four activities:

* A model of evolution by natural selection

* The requirements for evolution by natural selection

* Darwin's theory of evolution by natural selection

* The source of variation among individuals

During the first activity students can look at variation in the shell thickness distribution in the snail population as some of them are predated upon. Predictions can then be tested and subsequent observations allow the student to see which snails tend to get eaten and which ones tend to survive. At the end of this activity the evolution of the snails can be compared based on predator type (the student or the crabs).

The second activity deals with the various requirements for natural selection: variation, inheritance, and selection. Shell thickness can be made variable or non-variable, Shell thickness can be made heritable by clicking on the appropriate box. Also, survival can be made selective by clicking on the appropriate parameter. Students can make predictions about population distribution as they work on the activity.

During the third activity students can apply Darwin's theory by describing which conditions in the snail population would or would not allow evolution of a thicker shell. Finally, the role of mutation can be investigated by reproducing the snails with mutation and observing whether there is a limit as to how far predatory crabs can drive shell thickness in the snail population. …