Final answer:
Migration is an environmental factor that can influence natural selection and increase genetic diversity. Birds migrate and spread genetic variations across different populations.
Step-by-step explanation:
An environmental factor that could influence natural selection and increase genetic diversity is migration. Migration refers to the movement of individuals from one population to another. When individuals migrate to a new population, they bring with them new genetic variations, which can increase the genetic diversity of the population. For example, in birds, migration plays a crucial role in the spread of genetic variations across different populations.
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