Which concept explains the use of one's own phenotype to distinguish between kin and non-kin?

The correct concept explaining the use of one's own phenotype to distinguish between kin and non-kin is phenotypic matching. This phenomenon involves individuals comparing their own traits to the traits of others to assess relatedness. When an organism uses its own physical characteristics or behaviors to evaluate members of its species, it can help discern familial relationships. By recognizing similarities or differences in certain phenotypic traits, animals can make decisions that may enhance their inclusive fitness, such as providing more care or resources to kin, which share more of their genes.

The armpit effect specifically refers to a more nuanced application of phenotypic matching, where an individual relies on self-referent phenotype recognition to identify close relatives, particularly in environments where they might not have prior knowledge of their relatives' appearances. While this is related to the broader concept of phenotypic matching, it represents a specific case rather than the overarching process.

Behavioral genetics focuses on the interplay between genetics and behavior but does not specifically address how organisms distinguish kin based on their phenotype. Similarly, the nature vs. nurture debate explores the roles of genetic inheritance and environment in shaping behavior, yet it doesn't pertain directly to kin recognition through phenotype distinctions.