Definition · Plain-language
Natural selection
Natural selection is the process by which organisms better suited to their environment tend to survive and reproduce more, passing on their helpful traits.
The step most authors miss
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How natural selection works
Natural selection rests on a few simple observations. Within any species, individuals vary — they are not all identical. More offspring are produced than can survive, so there is competition for food, space and mates. Individuals whose particular characteristics happen to suit their environment are more likely to survive this struggle and reproduce. Because many characteristics are inherited, the survivors pass their helpful traits to their offspring. Over generations, the helpful traits become more common in the population, while less helpful ones fade. First set out by Charles Darwin, this is the core mechanism of evolution.
Variation, survival and inheritance
Three ingredients make natural selection possible. First, variation: members of a species differ in their characteristics, much of it caused by differences in their genes. Second, selection pressure: the environment favours some variations over others, so individuals with helpful traits survive and breed more successfully. Third, inheritance: those helpful traits must be passed on to offspring through genes. Where all three are present, the make-up of the population shifts over time. A classic example is bacteria becoming resistant to antibiotics, as the few resistant individuals survive and multiply.
Selection, not striving
A common misunderstanding is that organisms choose to change or develop traits because they need them. Natural selection does not work that way. The variation arises first, by chance, through differences in genes; the environment then "selects" which variations survive, simply by some individuals living and breeding more than others. An individual giraffe does not stretch its neck and pass on a longer neck; rather, giraffes that happened to have longer necks reached more food, survived better and left more offspring. Selection acts on variation that already exists.
Key facts
At a glance
- Definition: better-suited organisms survive and reproduce more, passing on traits
- Proposed by: Charles Darwin
- Also known as: survival of the fittest (fittest = best suited)
- Needs: variation, a selection pressure, and inheritance
- Result: helpful traits become more common over generations
- Importance: it is the main mechanism of evolution
Common misconceptions
What people often get wrong
Often heard: Organisms choose to develop new traits because they need them.
Actually: Variation arises first by chance, through gene differences. The environment then selects which variations survive — organisms do not consciously develop traits. A giraffe does not stretch its neck longer; those born with longer necks simply survived and bred more.
Often heard: "Survival of the fittest" means the strongest or fastest always win.
Actually: "Fittest" means best suited to the environment, not strongest or fastest. A trait such as good camouflage or disease resistance can matter far more than strength. Fitness is about surviving and reproducing in a particular environment.
Often heard: Natural selection changes an individual organism during its lifetime.
Actually: Natural selection acts on populations over generations, not on individuals within their lifetime. An individual cannot evolve; rather, the proportion of individuals with helpful traits changes across many generations.
Going deeper
