These questions ask you to distinguish a mutation from an acquired change and to put the stages of natural selection in the right causal order. The reliable method is to track where variation originates, which individuals reproduce, and what changes across generations.
Build the causal chain
Start with variation already present in the population. Mutation can create a new allele by changing inherited instructions, while sexual reproduction reshuffles existing alleles into new combinations. Mutations occur by chance rather than in response to need. Ionising radiation and some chemicals can raise the mutation rate, but mutations also occur without an outside cause. Most have little or no visible effect, although some are harmful or beneficial in a particular environment.
| Stage | Decision method |
|---|---|
| Origin of a new allele | Look for a change in the inherited base sequence. Selection and environmental change can alter frequencies, but they do not write a new allele. |
| Inheritance of a mutation | Ask which cell carries it. A change in a gamete can enter the next generation; a change limited to an ordinary body cell cannot. |
| Differential survival and reproduction | Compare each characteristic with the actual surroundings. Better fit, not size or strength by itself, raises reproductive success. |
| Population change | Follow allele frequencies over many generations. Individuals keep their inherited alleles during life; populations evolve as frequencies shift. |
The order matters: random variation first, environmental filtering second, inheritance third, and a frequency change after repeated generations. The environment does not instruct organisms to produce what they need. It changes which existing characteristics help their carriers survive and reproduce.
Wrong routes to reject
| Tempting account | How to correct it |
|---|---|
| Any visible change during life is a mutation | Check whether the inherited base sequence changed. Training, growth or a changed appearance can occur without any mutation. |
| An organism mutates because it needs a useful feature | Need does not direct changes in inherited instructions. Mutations arise without regard to whether their effects will help. |
| The strongest individuals are always selected | Fitness depends on the surroundings. Camouflage, patience or a smaller appetite may matter more than strength. |
| Natural selection creates a new allele | Selection changes the representation of alleles already present. Mutation is the process that can create a new version of a gene. |
| A helpful allele reaches the whole population immediately | Carriers must reproduce and pass it on repeatedly, so its frequency rises over generations rather than within every living individual. |
| One individual evolves during its lifetime | An individual may develop or acclimatise, but evolution is a genetic change in a population measured across generations. |
Try it
Which statements about the possible effects of a mutation are true? Select all that apply.
- Every mutation damages the organism in some way
- It can be harmful to the organism that carries it
- It can have no noticeable effect at all
- Every mutation shows up as a visible change
- It can be beneficial in the organism's surroundings
A mutation occurs in a cell of an adult animal. Under what condition can it be passed to that animal's offspring?
- Only if the cell is one that produces gametes
- Only if the mutation is a beneficial one
- If the cell is any cell in the animal's body
- Only if the same mutation occurs in both parents
Natural selection is often described as acting on variation. Where does the variation it acts on come from?
- Natural selection produces it as the conditions change
- From mutation and from the new allele combinations of sexual reproduction
- From the efforts individuals make during their lives
- It appears only in the offspring of the individuals that survive to breed