If you do not see an applet here, chances are that you are using Netscape with Mac OS. Not to worry you are only 8 clicks away from viewing this applet.

1. Please download the Apple Runtime for Java available for FREE at (if you already have the Apple Applet Viewer, skip to step 5):


2. Once the program has downloaded, click on the the MRJ2.2.2.smi icon on your desktop.

3. Click on the MRJ Install icon to install the applet viewer.

4. Open the Apple Applet Runner Folder

5. Click on the Apple Applet Runner Icon

6. In the file menu select Open location

5. Copy the URL of this page and paste it into the Location box of the Applet Runner window.

6. Click Open. The applet may take a moment or two to load.

It will be worth your time, I promise!

NOTE: You can also save the applet in your Apple Applet Viewer Favorites if you want to access it more quickly next time. Do the following:

When the applet is loaded, go to the applets menu and select add applet to list.

Natural Selection: Differential Mortality

The strength of natural selection is directly related to the degree of differential mortality in the population. If the probability of survival for an individual is a function of the value of a particular trait, then that trait is subject to selection pressures (assuming, of course, that the trait is heritable). Selection will not occur if the probability of mortality is the same for all individuals.

The relationship between mortality and a trait's value need not be a linear one for selection to occur. The probability of mortality may increase with the trait value, decrease with the trait value, increase with extreme trait values, increase for intermediate trait values or density dependent; an infinite array of possibilities exist.

Natural Selection: Differential Mortality

Adjust the amount of differential mortality to the right:

In this case the value chosen is the probability of mortality for individuals with a color value of 255. The probability of mortality is 0.0 for individuals with a color value of 0. Probability of mortality for individuals with intermediate color values is a linear function of the color value. This is an example of directional selection.