Final answer:
Genetic variation is the difference in DNA sequences between individuals that lead to unique phenotypes that can be inherited, making it a key factor in evolution.
Step-by-step explanation:
Variation among individuals that is due to variation in factors other than environmental influences is called genetic variation. Genetic variation is the difference in DNA sequences between individuals within a population. These differences contribute to the unique phenotypes seen in a population and can be passed down to offspring, making them a key target for natural selection. While the environment can cause individuals to look or act differently, only genetic differences can be inherited and thus affect the population's evolution over time.