Individuals with characteristics most suited to the environment are more…

The idea

This is the core of natural selection. Within a population, individuals vary because of differences in their genes, and some variants give a better fit to the local conditions. Those better-suited individuals are more likely to survive, and because they survive longer they are more likely to reproduce and pass their alleles on. A concrete case: in a population of beetles on green leaves, green individuals are harder for birds to spot than brown ones, so more green beetles live to breed. The environment does the selecting, not the organism, and no individual changes to suit the environment during its life. Selection acts on the variation already present, so the population shifts over generations rather than within one lifetime.

What earns the marks

• States that variation exists between individuals in a population, and that this variation is inherited.
• Explains that the environment presents a selection pressure, such as predation, disease or competition for resources.
• Links the characteristic to survival: individuals whose characteristics suit the environment are more likely to survive.
• Links survival to reproduction: survivors are more likely to breed successfully and so contribute offspring to the next generation.
• Uses a specific example, such as green beetles being camouflaged on green leaves, to show the selection pressure acting on a named characteristic.
• Avoids teleological wording: the organism does not choose to change, and the environment does not create the useful characteristic on demand.

Common mistakes and how to put them right

• Saying an individual 'adapts' during its lifetime to suit the environment.

  Put it right: Variation already exists and selection acts on it across generations.

• Treating survival alone as the endpoint.

  Put it right: Survival matters because it raises the chance of successful breeding, which is what changes allele frequencies.

• Writing that the environment causes the useful mutation when it is needed.

  Put it right: Mutations arise at random and selection then favours any that happen to be useful.

Exam tips

• Use the chain variation → selection pressure → survival → reproduction → inheritance, and make each arrow explicit in your answer.
• Name the characteristic and the pressure in your example, for example 'green colouration' and 'predation by birds', rather than writing 'better adapted' on its own.
• If a question says 'explain', give the mechanism; if it says 'describe', state the pattern without needing every causal link.