Natural Selection Simulator: Watch a Population Evolve in 3D
Rabbits with real genes live on a 3D island. Foxes hunt the ones they can see and catch, winters test their fur, and the survivors pass their alleles on: change the habitat and watch Darwin's natural selection, Hardy–Weinberg and genetic drift happen.
Darwin's checklist
Lab notebook
Every year's census (rabbits, the white allele's frequency, mean speed and fur, who died of what) and every change you make is written here. Export a CSV, or turn the session into a PDF lab report.
| # | When | What | Result | Value |
|---|
Concept library
Click "New problem" to begin.
Click "Start quiz" for 5 questions on Darwin's theory, types of selection, population genetics, misconceptions and a calculation.
1 Overview
Simulate shows a 3D island of rabbits on the left and live graphs on the right: Genes (allele and genotype frequencies), Traits (speed, fur and colour against the founding population), Population (rabbits, foxes and deaths by cause), Hardy–Weinberg (a χ² test) and Drift (replicate islands). Nothing is scripted: every rabbit carries genes, eats, breeds and dies, and evolution comes out of what happens to them. Experiment has six practicals that end in a PDF lab report, and Quiz has a practice quiz with worked solutions and a 5-question quiz.
2 Time and the island
- Press ▶ (or Space). At 1× one second is one day of rabbit life, so you can watch the hunts; 5× to 100× fast-forward (a year in 73 s to 4 s), and ⏩ 5 yrs runs five years at once.
- Drag to turn the island; hold Ctrl or ⌘ and scroll (or pinch) to zoom. Island, Follow and Fox move the camera; Follow rides with the selected rabbit and moves on to one of its kits when it dies.
- Click a rabbit to see its genotype, its traits, its parents and its kits. 🧬 Genes (G) puts genotype tags over the rabbits.
3 The rabbits: which traits get selected
Three inherited traits decide which rabbits live long enough to breed. The Rabbits panel names each one with what it helps and what it costs; the Traits now box under the graph shows how the population stands against the start and which way the island pushes it now (tap a row to see who survives):
- Fur colour (one gene, brown F dominant to white f): camouflage. A fox notices a rabbit that stands out from the ground much sooner.
- Hind legs → sprint speed (six genes plus environment): longer hind legs give a faster sprint, about 35 to 55 km/h. A chased rabbit must outrun the fox (about 48 km/h) until it gives up or reach a burrow. Long legs cost more food.
- Fur thickness (six genes plus environment): thick fur keeps a rabbit alive through a cold winter but overheats it in a hot summer.
🐇 Add rabbits on the island (key R) opens two choices. Release a group adds 5, 10 or 20 rabbits with the colour, legs and fur you choose: their genes start as a small share of the island's, and the Traits now box follows that share. If their traits suit the island it grows; if not, it shrinks or only drifts. New island sets the founders (white rabbits, legs, fur, island size). View → Mark rings the fastest fifth in green and the slowest fifth in red, the newcomers' descendants in purple, the hybrids (Ff, which look brown because brown is dominant) in orange, or the best of both in cyan: rabbits with the camouflage colour for the ground and a sprint faster than a fox. Crossbreeding shuffles colour and leg genes, so the kits of two lines can combine their strengths: the Best of both scenario crosses white, slow islanders with brown, fast newcomers, then brings the foxes, and Traits now counts the rabbits that got both; labels on the island show every chase: “✗ caught · 38 km/h” or “✓ escaped · 52 km/h”. The Survival graph compares the rabbits removed in the last 12 months (caught, or killed by cold) with the rabbits alive: that difference is natural selection.
4 Changing the environment
Island: the ground (meadow, forest floor, snow) decides which fur colour is camouflaged; the climate decides how cold the winters are and how much the grass grows. Selection: the number of foxes and the food. Genes: the mutation rate, a mutant rabbit, a random disaster (bottleneck), rafting six rabbits to a new island (founder effect), eight replicate islands that show drift, and the size and starting allele frequency of a new island. Five scenarios set everything up for one idea each.
5 Be the predator
Press 🦅 Be the predator at the top of the island (key H): the foxes leave and for 15 seconds you hunt by clicking rabbits. The rabbits you could not see survive and breed. It is the classroom camouflage (paper-dot) practical in 3D: you select, exactly as a fox does.
6 Darwin's checklist and the graphs
The checklist under the island ticks each of Darwin's ideas when the island shows it, with the evidence: the spread of speeds (variation), the parent–offspring slope (inheritance), kits born against kits that reached adulthood (overproduction), the speed and colour of the rabbits foxes caught against the rest (differential survival) and the change since the start (adaptation).
7 Experiment mode and the lab report
Six practicals: be the predator, Darwin's four postulates, Hardy–Weinberg equilibrium, genetic drift and island size, selection on running speed, and bottleneck and founder effect. Each shows its aim and a real-lab safety note; the method ticks off as you work, a conclusion question checks your result and Create lab report builds a PDF.
8 Units and keyboard
- SI | US switches km/h, mm, °C and m to mph, inches, °F and feet. Allele frequencies and counts have no units.
- Space plays or pauses, → runs 5 years, 1–3 pick the camera, G genotype tags, F Show me how, N a new island, S Status, Esc clears the selection. Right-click the island or a graph to save it as an image.
A natural selection simulator where evolution is not scripted
This natural selection simulator puts a population of rabbits on a 3D island and lets Darwin's theory play out. Every rabbit carries real genes and passes half of them to each kit. Foxes hunt the rabbits they can see and catch, winters test their fur, and the grass decides how many can live. Nothing in the program tells the population to change: it evolves because some rabbits leave more offspring than others, exactly as Charles Darwin argued in 1859.
- The island
- Rabbits with genes, grass, burrows, foxes, seasons; meadow, forest floor or snow; warm, mild or cold
- Genes
- Fur colour (brown F dominant, white f recessive), polygenic leg length and fur thickness, mutation
- Graphs
- Allele frequency, trait histograms, population, Hardy–Weinberg χ², genetic drift
- Modes
- Simulate, Experiment (6 practicals with a PDF report) and Quiz
- Price
- Free, no account or download; works on Chromebooks, tablets and phones
Darwin's theory of natural selection in four steps
| Darwin's idea | What it means | Where you see it on the island |
|---|---|---|
| 1. Variation | Individuals differ | Brown and white rabbits; sprint speeds from about 35 to 55 km/h |
| 2. Inheritance | Many differences are in the genes and are passed on | Kits of fast parents are faster than average (the parent–offspring slope) |
| 3. Overproduction | More young are born than can survive | Hundreds of kits a year; fewer than one in five reaches adulthood |
| 4. Differential survival | Those that suit the environment survive and breed more | Foxes catch more white rabbits on a meadow and more slow ones in a chase |
Put the four together and the result is adaptation: the next generation carries more of the alleles that helped their parents survive. A rabbit does not change its colour to match the snow, and it does not try to. The population changes, because the white allele is passed on more often when white rabbits survive more often.
Directional selection, camouflage and an ice age
Which rabbits get selected? Three inherited traits decide it: fur colour (camouflage), hind-leg length (sprint speed) and fur thickness (warmth), each shown with what it helps and what it costs. Release ten long-legged rabbits among short-legged ones with many foxes: the red “caught” labels go to slow rabbits, the Survival graph shows the caught rabbits were slower than the survivors, and within a few years the newcomers' genes make up several times their first share of the gene pool. With no foxes, their share only drifts. Start the Camouflage scenario: on a green meadow the foxes notice white rabbits from farther away, and in a few years the white allele is rare. Now choose snow. The same allele is suddenly an advantage, but it rises slowly at first: a recessive allele is hidden in brown carriers (Ff), and only the rare ff rabbits are white. This is directional selection, the pattern behind real camouflage such as the peppered moth in industrial England, rock pocket mice on dark lava and snowshoe hares that turn white for winter. The Speed race scenario pushes sprint speed up, while long legs cost food, so on a scarce island the advantage has a price.
The Hardy–Weinberg equilibrium
For one gene with two alleles at frequencies p and q, the genotypes of a population that is not evolving are p², 2pq and q², and p² + 2pq + q² = 1. The Hardy–Weinberg graph counts the island's FF, Ff and ff rabbits, compares them with those expected from p, and runs a χ² test (one degree of freedom, critical value 3.84). Choose No selection and the genotypes fit the equation year after year; add foxes on snow and the allele frequencies move. The equation is the null hypothesis that tells you evolution is happening.
Genetic drift, the bottleneck and the founder effect
Allele frequencies also change by chance. On a Tiny island of 25 rabbits, with no foxes at all, the white allele wanders up and down and can disappear in a few generations. Run 8 islands shows the same start ending in different places. A Disaster kills most rabbits at random (a bottleneck), and Raft away starts a new island from six rabbits (the founder effect): both change the gene pool without any adaptation. Drift is strongest in small populations; selection is the only process that makes a population fit its environment.
Practicals and course links
| Practical | What you find out | Course links |
|---|---|---|
| Be the predator | Camouflage decides who is caught | NGSS HS-LS4-4; GCSE 4.6.2 |
| Darwin's four postulates | The evidence for each step of natural selection | NGSS HS-LS4-2; IGCSE 18 |
| Hardy–Weinberg equilibrium | p² + 2pq + q² and a χ² test | AP Biology 7.4–7.5; NCERT 12 |
| Genetic drift and island size | Why small populations drift | AP Biology 7.3; NGSS HS-LS4-3 |
| Selection on running speed | A shift in the mean of a trait | NGSS HS-LS4-3; IB D4.1 |
| Bottleneck and founder effect | Chance events that change the gene pool | AP Biology 7.3 |
Who uses this natural selection simulator?
High school students meeting Darwin's theory and the evidence for evolution (NGSS HS-LS4, AP Biology Unit 7, GCSE and IGCSE), students practising Hardy–Weinberg problems, and teachers who want a free evolution simulator for a classroom screen or Chromebooks. It is an educational model of real processes, with simplified numbers.
Frequently asked questions
What are the 4 main ideas of Darwin's theory of natural selection?
Variation: individuals of a species differ from each other. Inheritance: some of those differences are passed from parents to offspring in their genes. Overproduction: more offspring are born than the environment can support, so there is a struggle to survive. Differential survival and reproduction: individuals with traits that suit the environment survive and breed more often, so their alleles become more common in the next generation. Over many generations the population becomes adapted to its environment. Individuals do not evolve; populations do.
What is the difference between natural selection and genetic drift?
Natural selection changes allele frequencies in a consistent direction because some alleles help their carriers survive and reproduce, so it produces adaptation. Genetic drift changes allele frequencies at random because of chance: which individuals happen to breed, which offspring happen to survive. Drift has no direction, does not produce adaptation and is strongest in small populations, where it can make an allele disappear or become fixed in a few generations. The bottleneck and founder effects are cases of drift.
What is the Hardy–Weinberg equation?
For a gene with two alleles at frequencies p and q (p + q = 1), the genotype frequencies in a population at equilibrium are p² (homozygous dominant), 2pq (heterozygous) and q² (homozygous recessive), and p² + 2pq + q² = 1. The frequencies stay the same from generation to generation only if there is no natural selection, no mutation, no migration, random mating and a very large population. If you know the share of recessive individuals you can find q as its square root. A chi-square test checks whether observed genotype counts fit the equation.
Explore related simulators
See how one gene's alleles are dealt to offspring in the Interactive Punnett Square Calculator, and where new combinations of alleles come from in the Meiosis Simulator. Foxes and rabbits are links in a food web: build one with Build the Food Chain. Mutations are changes in DNA: try them in the Interactive Codon Chart, and see natural selection in microbes as antibiotic resistance in the Virtual Bacteria Simulator.
Sources: Darwin (1859), On the Origin of Species; OpenStax Biology 2e, chapters 18 and 19; Urry et al., Campbell Biology 12th edition, chapters 22 and 23; Nachman, Hoekstra and D'Agostino (2003), PNAS 100, on rock pocket mice; Cook et al. (2012), Biology Letters 8, on the peppered moth; Mills et al. (2018), Science 359, on snowshoe hares. Rabbit and fox speeds, litter sizes and breeding seasons follow published natural history; the simulator is an educational model with simplified numbers.
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