  The drive for economy is itself a biological instinct, which science must thus also fulfill. In a larger sense, economy is tied to the innate tendency toward survival or search for better orientation discussed earlier. Evolution is guided by these principles; life as a product of evolution has a tendency toward these principles, and we as humans have these tendencies hard-wired into us—even to the point that our very conception of self-existence arises out of it; in Analysis of Sensations, the ego is described as arising from an “ideal mental economical unity.” [AS: 22]