Final answer:
Human variation is categorized into genetic and environmental factors. Genetic variation arises from different alleles and inheritance patterns, while environmental variation depends on lifestyle and social conditions. Natural selection affects heritable genetic diversity, and race is considered a weak biological construct.
Step-by-step explanation:
Generally, human variation is divided into two broad categories, which are genetic and environmental. Genetic variation refers to differences in DNA among individuals, which can manifest in diverse traits. Environmental variation is attributed to factors such as nutrition, social status, and access to healthcare.
These differences among humans are influenced by several genetic mechanisms, including autosomal dominance and recessiveness, X-linked dominance and recessiveness, incomplete dominance, codominance, and lethality. Mutations, which are changes in the nucleotide sequence of DNA, also contribute to genetic variation but are not necessarily inherited. On the other hand, traits like skin tone, eye color, and hair texture are hereditary and show how a person's genetic make-up can create observable phenotypes.
Natural selection acts on heritable traits, influencing the genetic diversity within populations. However, it is important to acknowledge that there is more genetic variation within given racial categories than between them, making race a weak construct in biological terms.