Final answer:
Geographic variation in different populations occurs due to geographical separation, leading to phenotypic variation such as larger body sizes in warm-blooded animals in cooler climates (latitudinal cline) and flowering times in plants along mountain slopes (altitudinal cline).
Step-by-step explanation:
Geographic variation, or the distinctions in the genetic makeup of different populations, often occurs when there is geographical separation between populations. This separation can lead to phenotypic variation between the populations due to restricted gene flow and different environmental pressures. An example of geographic variation is the increasing body size of warm-blooded animals in cooler climates near the poles, a phenomenon known as a latitudinal cline. Other examples include temporal differences in flowering among plants along an altitude gradient, called an altitudinal cline, and the varied genetic characteristics among human populations across different regions of the world, including differences in stature, facial features, and skin color.