Peppered Moth Game Worksheet Answers

Natural Selection and the Peppered Moth Simulation

Most biology teachers assign the Peppered Moth interactive as a way to demonstrate natural selection in real time. The game lets you act as a predator (usually a bird) selecting moths against different backgrounds. You click or tap moths to eat them, then the surviving population reproduces based on their color traits. After several rounds, you see the shift from light to dark populations on soot-covered trees, and back again when pollution drops. I've seen this worksheet dozens of times across different school districts. The questions usually follow a predictable pattern, though the exact wording varies by teacher. Here's what most assignments are asking for and how to approach each section. Part one typically asks you to record data. You'll run the simulation twice—once on a light background and once on a dark background. Your table should look something like this:

Light background trial: Light moths start at 50, dark moths start at 50. After the first generation of predation, you might eat 20 light moths and 35 dark moths. That leaves 30 light and 15 dark surviving. Those survivors reproduce, and the next generation might be 45 light and 25 dark, depending on how many offspring each produces per the simulation's rules. Dark background trial flips the trend. You eat more light moths because they're visible against the dark bark. The dark moths survive at higher rates, and over successive generations the population skews heavily toward the melanic (dark) form. Part two asks interpretation questions. The standard answer is that birds act as the selective pressure. Moths that contrast with their background get eaten more often. Moths that match their background survive and pass on their genes. Over multiple generations, the population shifts to match the dominant background color. That's directional selection driven by predation.

Part three usually asks about environmental change. If the environment switches back—say, through cleaner air and lichen regrowth—the light moth population recovers. The worksheet expects you to connect this to the real Industrial Revolution history of England, where soot from factories darkened tree trunks and the moth population shifted accordingly. When the Clean Air Act came through in the mid-1950s and pollution dropped, the trend reversed. I ran into a specific issue last year with a version of the game that used a randomized seed instead of a fixed population starting count. One student submitted data that showed no significant change between generations, which should have been impossible. The problem was she clicked moths in the wrong order during the predation phase, causing the simulation to register her selections incorrectly. The workaround was simple: restart the round and click methodically from left to right, making sure each moth registered as eaten before moving to the next one. Some versions of the game have a lag or a visual bug where clicking too fast skips a selection. Slow down your clicks. It takes longer but the data comes out clean. Another thing that catches people out is the mutation rate setting. Several worksheet versions include a checkbox or slider for mutation, and if it's left on high, the results look scrambled because new color variants appear faster than selection can act on them. Turn mutation down to zero or the lowest setting before starting. Otherwise your data table will show erratic jumps that don't demonstrate clear directional selection, and your teacher will think you ran the experiment wrong.

Deeper Nuances Most Students Miss

One counter-intuitive point: the game models a single-gene trait, but real peppered moth coloration involves at least a couple of genetic loci interacting. The simulation simplifies this for educational clarity, and that's fine, but it means the results will always look cleaner and faster than what happens in actual field studies. Don't cite the game's generation-to-generation speed as evidence that evolution is slow—opposite, in fact. The game compresses time significantly. Another thing worth noting is that the simulation doesn't model other selective pressures. In reality, moths face temperature regulation differences based on melanin content, parasitic wasp attacks, and behavioral avoidance. The worksheet focuses narrowly on bird predation because it's the clearest mechanism to demonstrate, but that narrow framing can make natural selection look like the only force at work in evolution. It isn't. Genetic drift, gene flow, and pleiotropy also matter. The worksheet won't tell you this, but it's worth understanding when you write your conclusion section.

Download and Access Notes

The most widely used version runs through the Howard Hughes Medical Institute's BioInteractive platform. The direct link is hhmi.org/biointeractive/pepperedmoth. There are also archived versions floating around on classroom resource sites, some of which bundle the worksheet PDF directly. If your school's network blocks the HHMI link, the Game Biology version hosted through various university education pages tends to work as a fallback. I've found that the HHMI version loads more reliably and has fewer graphical glitches during the predation phase, which matters when you're recording second-by-second selection data. A few schools use a slightly older flash-based copy hosted by McGraw-Hill or Pearson. Those versions have different question banks and sometimes different answer keys, so check which one your teacher is referencing before you start filling anything out. Mismatching the worksheet to the wrong game version is an easy way to get your numbers wrong even when your understanding is solid.

What the Worksheet Gets Wrong and Where It Falls Apart

The simulation treats every moth of the same color as equally likely to be seen and eaten. In nature, individual variation matters—wing spot size, resting posture, and microhabitat choice all influence predation risk. The game also assumes a closed population with no migration, which means your data will show clean directional shifts that real populations rarely produce without some gene flow from neighboring areas. There's also the issue of sample size. Most worksheet versions start with 50 moths of each type, and you eat roughly half per generation. With small samples, random chance can dominate selection in early rounds, producing noisy data that doesn't clearly show the trend until you reach generation three or four. If your first two rounds look inconclusive, don't panic—keep going. The pattern emerges by round four or five in the vast majority of trials. If your class requires a more rigorous statistical analysis, you'll want to supplement the game data with a chi-square test comparing observed versus expected frequencies. The worksheet rarely asks for this, but it's what you'd actually do in a college-level lab. Running that test manually takes about twenty minutes and adds legitimacy to your report that the game data alone doesn't provide.

The Peppered Moth Game Worksheet Answers you need are straightforward if you run the simulation carefully, keep mutation off, and read the questions before you start clicking. The harder part is explaining the limitations of the model in your conclusion, which is usually where graders look for depth. Don't just repeat the obvious natural selection explanation. Address the simplifications, mention the single-trait assumption, and note that real populations move through selection in messier ways than a browser game can show. That's the difference between a C and an A on this assignment.