Fact 1: Gene flow occurs when individuals move into or out of a population.

Fact 2: Populations Populations are subsets of a species.

Given the two facts above, answer the question "Gene flow occurs when individuals move into or out of a subset of a what?" with the following options: 
- animals
 - mammals
 - humans
 - plants
 - goats
 - offspring
 - Species
 - alleles


 

       Species  