Prior to the industrial revolution, most of the individuals in the peppered moth population were lighter in color with only a small percentage of individuals having a dark color.    Once the industrial revolution started, air pollution was common, including lots of coal dust from factories. 

During the industrial revolution, fewer light-colored moths were observed and more dark-colored moths were observed.  By the late 1800's most of the population was dark. 

After some discussion, students came to the following conclusions:

1. The ability to blend in to the environment reduces that number of moths that are eaten by birds.

2. The more moths that survive, the more moths that reproduce 

3. Since genes control the color of the moth, and genes are passed down from parents to offspring, then the offspring are more likely to look like their parents. 

So, in the early 1800's, prior to the industrial revolution, the moth population in England was mostly light colored moths with a few dark-colored moths.  As towns became industrialized, the soot from burning coal covered many of the surfaces, making the surfaces darker.  As a result, the light colored moths were easier to see and were eaten by birds more often.  Conversely, the dark-colored moths blended into the the darker background and were eaten less by birds.  

Since greater percentage of black moths survived, reproduced, and passed their genes for the dark color to their offspring, the percentage of dark colored moths increased the following year.   Because greater percentage of light-colored moths were eaten by birds, a smaller percentage of light-colored moths were able to reproduce.  So, in the following year the percentage of light-colored moths that were born was less. 

As this happened from year to year, the dark color moth became more common and the light colored more became less common until the entire population was mostly dark colored moths. 

1. From Genetics - Traits are passed down from parents to offspring

2. Traits cannot be passed down from parents to offspring if the parents do not survive

3. Survival depends on favorable traits - Camouflage in this case

4. Genetic variation is favorable for the survival of a species (if there had not been any dark peppered moths, then the species may have gone extinct)