Here's a breakdown:
* Survival: The ability to live long enough to reproduce.
* Reproduction: The ability to produce offspring that are also capable of surviving and reproducing.
Fitness is often measured by the number of offspring an individual produces that survive to reproduce themselves. The more offspring an individual produces, and the more of those offspring survive to reproduce, the higher their fitness.
It's important to note that fitness is a relative term. An organism may be more fit than another in a particular environment, but less fit in a different environment.
