1Individuals vary
In any population, individuals vary, partly because their genes differ. Peppered moths, for example, can be pale and speckled or almost black, and the colour is inherited.
Lesson 28.3 notes
Natural selection
Variation, competition and survival, passing on genes, peppered moths, Darwin and Wallace, and the evidence for evolution.
2Competition
Living things produce more young than can survive. A frog lays thousands of eggs, but only a few grow into adults: the tadpoles compete for food and space, and many are eaten.
3The best adapted survive
The individuals best suited to their environment are the most likely to survive. On pale, lichen-covered bark, birds spot and eat more of the dark moths.
4Passing on genes
The survivors breed and pass on their genes, so their offspring tend to have the same useful characteristics, such as the colour that hides them best.
5Over many generations
Generation after generation, a useful characteristic becomes more common. This is natural selection. It makes a species change over time: evolution. Over a very long time, new species can form.
natural selectionevolution
6Peppered moths
In the 1800s, soot from factories blackened tree bark near cities. Dark moths were better hidden there and became common. Since clean-air laws in the 1950s, pale moths have returned.
7Darwin, Wallace and the evidence
Charles Darwin and Alfred Russel Wallace proposed natural selection in 1858. Evidence includes fossils, finches with beaks suited to different foods, and bacteria that evolve resistance to antibiotics.
Explore: Moth lab
Choose pale or sooty bark, then let the birds feed, one generation at a time. Watch the share of dark moths in the population change.
Common mistake: Natural selection changes populations, not individuals
A pale moth can't decide to turn dark. Dark moths that already exist survive better on sooty bark and have more offspring, so over many generations more of the population is dark.
Remember
- Individuals vary, and they compete for what they need: animals for food, water, space and mates, plants for light, water, space and minerals. Those best adapted to their environment are the most likely to survive.
- Survivors reproduce and pass on their genes, so useful characteristics become more common over generations: natural selection.
- Darwin and Wallace proposed natural selection in 1858. Evidence includes fossils, peppered moths and bacteria that resist antibiotics.
Going further at GCSE