Biology asks two basic questions, "how" and "why," referring to mechanism and function respectively. How do we see? With our eyes. Why do we see? To find our way, recognize people and objects, and so on.
The last great frontier of Science is consciousness - the ability to experience, desire, enjoy, suffer, intend, and so on. Without understanding HOW it works, we here suggest an answer to the WHY question. Namely, consciousness evolved in order to allow incentives to operate; and these, in turn, greatly facilitate the process of living. Inter alia, one might say that economic mechanism design, which is based on incentives, is enabled by evolution's "design" of consciousness.