Please read the explanation at the bottom before playing with the animation.

First a practical matter: this interactive animation needs to be centered on your screen as best as possible and then not moved while you're playing with it. The trouble is, some elements will be erased every time something else - like another window - temporarily overlays them. This isn't a big deal, because the control buttons will stick around, and it can always be replayed.

Having said that, let me explain what's going on. Before the animation starts there is a single reproductive entity. After each generation each entity on the screen has a 50% (probability = 0.5) chance of spontaneously reproducing a clone of itself. What you the viewer see initially is the situation after ONE generation, so there will be either one or two of the entities on the screen. In the upper lefthand corner of the screen is the (leftarrow) new generation button, which will cause another generation to pass. So after two generations you may have one, two, three or four of the entities. You can have a maximum of 20 generations before control is taken out of your hands and the generation button disappears (much beyond that and you'll end up waiting for a long time for each generation to pass). Meanwhile, down in the lower righthand corner is an all-done button. If you push it before the generation button goes away it will stop the generations where they are. Push it again and you'll first get a theoretical green graph of how the population is expected to grow, and then a reddish point plot of how it actually grew over however many generations were allowed to pass. (If you use up all the allowable generations, then the first push on this button will produce the graphs.)

Finally, once you've got the graphs on the screen the left arrow button reappears, and you can use it to restart the whole thing. The experimental curve should be different every time, and occasionally will not look too close to the theoretical curve, but on average it will be pretty close. Play with this a few times, then we'll talk again on the next page.