The survival of an organism depends on its ability to sense and respond to the external environment. In all environments, organisms with similar needs compete for the same resources. These two facts fuel the process of natural selection.
Natural selection can occur if the following criteria are met:
1. Overproduction:
A species produces more offspring than will survive to maturity.
2. Genetic Variation:
The individuals within the species’ population are all genetically slightly different from each other.
3. Struggle to Survive:
Individuals of the population must struggle to avoid predators and find food and shelter.
4. Successful Reproduction:
Individuals that are successful at surviving are able to reproduce and pass on their genes to their offspring.