Final answer:
Variation among individuals due to non-genetic factors is called environmental variation, which includes the influence of diet, climate, and other non-genetic factors on an organism's phenotype.
Step-by-step explanation:
Variation among individuals that is due to factors other than genetic factors is called environmental variation. Phenotypic variation in a population can result from a complex interplay of both genetic factors and environmental influences. For instance, two individuals with the same genotype can have different phenotypes due to differences in their environments, such as variations in diet, climate, or exposure to diseases. Environmental variation highlights the impact of non-genetic factors, contrasting with genetic variation, which is passed down to offspring and subject to natural selection. It's important to recognize that variation can arise from many sources, and the level of heritability is the fraction of phenotypic variation that can be attributed to genetic differences among individuals in a population. While genetic variation is critical for evolution, environmental factors play a significant role in shaping the observable traits of organisms within a population, as seen in examples like temperature-dependent sex determination in some reptiles or skin color affected by sun exposure.