Final answer:
Trait variations within a species allow us to investigate individual differences due to genetics and environmental factors, which are essential for natural selection. These variations must have a genetic basis to be heritable.
Step-by-step explanation:
Trait variations are critical for understanding a range of biological phenomena, including the differentiation of individuals within a species. When exploring within-species trait variations, we primarily investigate individual differences within a species. This involves looking at how certain traits can vary amongst individuals of the same species because of differences in their genetic makeup or due to the influence of environmental factors.
Trait variations allow for natural selection to operate by selecting for alleles that confer beneficial traits or behaviors and selecting against those that have detrimental effects. Importantly, for natural selection to act on these variations, they must be heritable—that is, they must be encoded in the individual's genes and able to be passed onto offspring. Environmental factors can also lead to phenotypic variations, such as changes in skin color due to sun exposure, which are not necessarily heritable.