Final answer:
Biological variation among human populations is influenced by genetic and environmental factors, resulting in diverse physical traits such as skin pigmentation and the sense of smell.
Step-by-step explanation:
The biological variation between human populations can be explained by both genetic and environmental factors that have influenced human evolution over time. These variations manifest in different physical traits such as height, facial structure, and skin pigmentation, which are the outcomes of adaptation to diverse environmental conditions, such as varied levels of ultraviolet radiation, climate, diet, and geographic isolation. For example, skin pigmentation differences arose as a response to the levels of UV radiation, with darker skin providing protection from the sun's rays in areas with high UV exposure, and lighter skin allowing for vitamin D synthesis in areas with lower UV exposure.
An example of a physical trait that varies among human populations is the sense of smell. This trait may experience variation due to biochemical differences within populations, and it can influence an individual's food preferences and perception of the environment. Such traits are the result of long-term adaptations and are subject to evolutionary forces like natural selection, genetic drift, and gene flow.