Final answer:
Genetic variation or genetic diversity refers to the genetic differences between individuals within a species, which is critical for evolution. It can manifest as a range of phenotypes affected by geographic factors leading to clines.
Step-by-step explanation:
The variation among members of different species is known as genetic variation or genetic diversity. This variation is the result of genetic differences between individuals, and it is essential for the process of evolution. Examples of population variation can include differences in phenotypes such as the size of warm-blooded mammals near the poles or the myriad fur colors in domestic dogs. Geographic factors, like climate and altitude, often lead to what is known as a cline - a gradual change in certain characteristics of a species along an ecological gradient. This phenomenon results in the latitudinal cline observed in animals with larger body sizes in colder climates and the altitudinal cline seen in plants that bloom at different times based on their elevation on a mountain.