What does the term adaptation most commonly refer to?

The term "adaptation" most commonly refers to changes within a population seen over time. This concept is rooted in evolutionary biology, where adaptations are traits or characteristics that enhance an organism's ability to survive and reproduce in its environment. These traits arise through the process of natural selection, whereby advantageous variations become more common in subsequent generations as individuals with those variations are more likely to survive and reproduce.

In contrast to the other options, which focus on changes within individual organisms, adaptation in the evolutionary sense specifically highlights the demographic changes occurring over long periods within a population rather than transient physiological or behavioral changes that might occur in individual organisms. Thus, the correct understanding of adaptation emphasizes the collective shifts in traits among members of a species, driven by environmental pressures and genetic variation.