Pondscum

• Vary the amount of food added per generation.
• Adjust the food quality.
• Set the cell mutation rate.
• Disallow specific cell movements (turns).
• Limit the area where food grows.
• Fiddle with the food needed to reproduce.
• Finally, set the speed and scale of the simulation to suit your specific demonstration needs.

Real-time plots of mean gene frequencies and population / food dynamics let you monitor your evolving pond. As the population runs through many generations, the cells that get less food will die while those getting more reproduce.

Reproduction produces mutations in movement control genes. Some movements (especially the backward move) are decidedly poor at gathering food. Cells that don't effectively gather food have limited reproductive success which gradually eliminates those traits from the gene pool. Pondscum vividly illustrates this.

Several classroom demonstrations / experiments can be pursued:

• Natural selection - the cells on the screen are the real-time descendents of previous generations. Only the products of successful food gathering and reproduction will be there. Competition for food does alter the turning genes in the evolving cell population.
• Extinction - students will produce this effect early in test runs. Reducing food supply will drive down the population toward extinction levels.
• Population cycles - the population for a given pond configuration trends toward a steady state but is not static - it will fluctuate around some equilibrium value.
• Predator-Prey cycles - the population graph tells the story - as food algae rises the cells rise too, until their exploding numbers devour too many algae. The algae population crash produces a subsequent cell population crash. The offset peaks on the two populations shows the reciprocal relationship of the two.
• Niche adaption - by limiting the food production area, the genotype necessary to be successful is changed. For a large area, long, sweeping turns produce the most food (lots of forward and forward-left and forward-right genes). For a tight area, these long turns will take the cell out of the food area. Many more left and right turn genes emerge. This produces tight-turning cells that better stay in the food area.
• Genetic drift - when the population gets small, a few mutations can dramatically affect the genetic make up of the population. With small populations, the pie charts wriggle wildly as chance survival of certain individuals produce alteration of gene frequencies.
• Carrying Capacity (K) - how many cells can an individual habitat support? Alter the food amount and nutrition value and find out.
• Micro environment - Zoom in to show bigger critters and watch the microenvironment of an individual cell. Watch the struggle for food as cells compete with others in their vicinity for scarce food resources. Critters with the best turning gene mix win this showdown for survival.

Pondscum runs on all 32-bit Windows (95, 98, NT, 2000 and XP) platforms. Download the December 26, 2004 version 0.5c (about 330k).

To install, open (run) the downloaded file which will install the program (just 2 files) to the folder of your choice. Shortcuts will appear in your start menu for running and uninstallation.

If you would like to help PondScum evolve beyond fractional version numbers, or just want to get some friendly program support, please consider donating to the project through PayPal by clicking the button below,

 Michael Mardesich
 124 NE 58
 Seattle, WA 98105

Release history ...
- 0.5c Moved food garden to corner of the pond. Added gene plots of cells in the garden and outside the garden. Forced tracked cell to always render. Changed mutation options. - 0.5b Added some food (1/16) to the rest of the pond in food localization mode. Added keyboard shortcuts for step and track new buttons.
- 0.5a Changed tracking gene display from text to pie chart.
- 0.5 Added ability to track one critter.
- 0.4b Faster graph rendering and distributed in a standard Windows installer (.msi) package. - 0.4a Fixed bug in new genome mechanism. - 0.4 Increased possible cell turns in genome from four to eight and made them switchable. Also fixed resizing bug.
- 0.3 Larger cell capacity; food vs time plot; show parameter slider values; fixed bug that appeared on machines with less than "true color" (32 bit) video.
- 0.2 Initial public release.