Answer:
Mutation
Step-by-step explanation:
The main cause of variation within a population is usually through genetic mutation.
Mutation is the alteration of the genetic sequence within an organism. It often lead to formation of new genetic patterns and codes.
Most times, environmental influences are paramount to causing genetic mutation within a population.
Other times, it might be due to competition and some other internal factors.
Mutation can be transferred from parents to offspring in most cases.