Moths on a trunk: natural selection in action
"Moths on a trunk: natural selection in action" is a free, interactive Class 12 Biology simulation for NEET, built on the lesson "Natural selection seen in action" in Evolution. The population starts with 1 dark moth in 10. Drag the generations forward on a sooty trunk, then switch to a lichen-covered trunk and drag again. This is a simple model, not real counts. Predators pick out the moth that contrasts with the trunk. On soot the dark form rises; on lichen it falls. The variation was already there; selection only changed the proportions.
From the lesson Natural selection seen in action in Evolution. Change the values and watch what happens.
The idea behind it
NCERT §6.3
- In England, moths collected in the 1850s, before industrialisation, were mostly white-winged; dark-winged (melanised) moths were fewer.
- A collection from the same area in 1920, after industrialisation, had more dark-winged moths: the proportion had reversed.
- Explanation: predators spot a moth that contrasts with its background. Before industrialisation, trunks were covered by thick, almost white lichen, so white moths survived and dark ones were picked off.
- After industrialisation, smoke and soot darkened the trunks and lichens could not grow; now the white moths were eaten and the melanised ones survived. Moths that could camouflage themselves survived.
- Lichens do not grow where the air is polluted, so they can be used as indicators of industrial pollution.
- Support: in rural areas without industry, melanic moths stayed few. In a mixed population, the better-adapted survive and increase, but no variant is completely wiped out.
- Heavy use of herbicides and pesticides has selected resistant varieties within a short time. The same holds for microbes treated with antibiotics and for eukaryotic cells treated with drugs: resistance appears in months or years, not centuries.
- These are examples of evolution by anthropogenic action. They also show evolution is not directed in a deterministic way: it is a stochastic process resting on chance events in nature and chance mutations in organisms.
Questions
2 answers
- What does the "Moths on a trunk: natural selection in action" simulation show?
- The population starts with 1 dark moth in 10. Drag the generations forward on a sooty trunk, then switch to a lichen-covered trunk and drag again. This is a simple model, not real counts.
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Natural selection seen in action" in Evolution (Class 12 Biology).
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