Five basic components of natural selection:
1. Individuals within a population are not identical. They vary, sometimes only slightly in structure, function and behaviour.
2. Some of this variation is heritable, determined by the organism's genetic make-up, and can be passed from parent to offspring.
3. All living things have a tendency to overproduce. More offspring are produced than are required to keep the population stable.
4. Despite overproduction, populations tend to remain relatively stable. Thus many individuals fail to survive and reproduce.
5. Different individuals leave different numbers od descendants.