Final answer:
Physical variation by visual inspection, like skin and hair color, refers to an organism's phenotype, including traits influenced by genetics and the environment. The study of these traits is part of biological anthropology, including the influence of X-linked genes and sexual selection.
Step-by-step explanation:
The description of physical variation by visual inspection, such as skin, eye, hair color, and physique, refers to the concept of phenotype. A phenotype encompasses the set of observable characteristics or traits of an organism. This includes direct observations of physical traits, such as those influenced by both genetics and environmental factors like sunlight. For example, the trait variation in the physical appearance of a heritable characteristic can include the pigment melanin which affects hair color, or height which can be influenced by genetics and nutrition.
X-linked genes, which are present on the X chromosome but not the Y chromosome, contribute to these phenotypic differences, especially in sexual dimorphism, where physical characteristics differ between males and females. The study of these variations, including the many forms they take such as differences in skin pigmentation due to sun exposure, is a key aspect of biological anthropology, and connects to the broader topics of population variation and sexual selection.