Abstract
Elsewhere, I defend the “causal interactionist population concept” (CIPC). Here I further defend the CIPC by showing how it clarifies another concept that biologists grapple with, namely, environment. Should we understand selection as ranging only over homogeneous environments or, alternatively, as ranging over any habitat area we choose to study? I argue instead that the boundaries of the population dictate the range of the environment, whether homogeneous or heterogeneous, over which selection operates. Thus, understanding the concept of population helps us to understand concepts of selective environment, exemplifying the importance of the CIPC to other concepts and debates.