One of the most easily understood examples of how natural selection works is the case of the peppered moths in Britain. The peppered moth was white with black speckles. But in 1848, a black form was recorded for the first time in Manchester. By 1895, 98 percent of the peppered moths in Manchester were black. They spread to other parts of England and thrived in the regions where factories spewed pollution, making nearby cities like Manchester dingy.

A 19th century scientist J.W. Tutt thought maybe the black moths did well in these more polluted areas because their colour gave them an advantage — camouflage. Moth-munching birds could more easily see, and then eat, the white moths. In the 1950s, another scientist, Bernard Kettlewell, experimented to see if this was true. What do you think happened?

• 60 red toothpicks

• 60 yellow toothpicks

• 60 blue toothpicks

• 60 green toothpicks

• Ruler

• Coloured pencils

• Timepiece

• Calculator

1. Randomly throw all the toothpicks throughout a predetermined area. (Our area was a grassy patch of lawn, outlined by leaves. But you can adapt this project for use in snow, sand, or even on a rug.)

2. The different-coloured toothpicks represent four subspecies (a subdivision of a species; for example, dogs, wolves, and dingos are all subspecies, related but distinct from each other). You are the predator. These toothpick “creatures” are the prey. Using a timer, give yourself one minute to track down as much “lunch” as you can.

3. Count how many of each toothpick subspieces you found.

4. Using your coloured pencils and ruler, make two bar graphs. Your first graph will show the number of toothpicks of each colour found. This percentage is calculated as follows:

Number found ÷ Number distributed = Percentage found

As an example, we found 14 blue toothpicks. So the percentage left is:

14 ÷ 60 = 23.3%

Your second graph will show the percentage of each toothpick subspecies remaining. This percentage is calculated as follows:

Number distributed – Number found ÷ Number distributed = Percentage left

As an example, we found 14 blue toothpicks. So the percentage left is:

(60 – 14) ÷ 60 = 46 ÷ 60 = 76.7%

5. Analyze your bar graphs and consider these questions: which subspecies was the hardest to find? Which subspecies was best adapted to its environment? What would happen to the subspecies that was the least well adapted? What would happen to the species that was the best adapted?

In a simple way, this experiment is simulating what happened to the Manchester moths. In our experiment, the blue-coloured toothpicks were easiest to see on the lawn, so the “predator” ended up catching more blue “prey”. The green-coloured toothpicks were hardest to see on the lawn, so only a few were “caught”.

Look at our graph of the “remaining colours of toothpicks”: more green means more breeding green pairs left in the environment to reproduce. Fewer blue means fewer breeding blue pairs left to reproduce. What will eventually happen after a series of generations? Green should eventually become the dominant colour.

This is what happened to the peppered moths. In a polluted environment, the black moths were more camouflaged and less likely to be seen and eaten. When new anti-pollution laws were adopted, the environment was cleaned up and the whiter moths made a comeback.

Some people attacked the original research for a number of reasons, one being that bats were the moths’ main predators and bats use echolocation, not sight, to hunt. So, scientist Michael Majerus conducted a six-year study on the moths, from 2001 to 2007. His data backed up Kettlewell’s evidence. And, in fact, Prof. Majerus witnessed robins, hedge sparrows, blackbirds, starlings, magpies, and wrens among the birds that ate the moths. Prof. Majerus also observed that unlike 100 years ago, the white moths now have the camouflage advantage.