What does variation refer to in biology?

Variation in biology refers to the differences between organisms within a species or between different species. This concept is essential because it highlights how these differences can impact survival, reproduction, and the overall dynamics of ecosystems. Variations can occur in numerous traits such as physical characteristics, behaviors, and physiological responses. Understanding variation is crucial for studying evolution, as it is the raw material upon which natural selection acts, leading to adaptation and evolution over time.

In contrast, while observable traits are a component of variation, they do not encompass the entire concept. Adaptation refers specifically to changes that make an organism better suited to its environment, which is a result of variation but not what variation itself defines. The range of habitats in a biome relates to ecological diversity rather than the biological differences among organisms. Thus, the correct answer captures the essence of biological diversity through the lens of the differences that exist among living things.