Concepts have a central and important place in science, therefore, it is important that their meanings are always made clear. However, such clarity does not always exist, even in the case of such fundamental biological concepts as "gene" and "adaptation." A quick look at textbooks reveals that different meanings may be attributed to the same concept, even within the same textbook, without explicitly discussing the differences of those meanings. This can be misleading, and mask important conceptual differences. Therefore, the differences between the various meanings of the same concept should be discussed and explained in order for conceptual understanding to be achieved.