This paper describes an evolutionary method of technology integration for the development of a Lunar base life support system. The baseline is a partially-closed Regenerative Life Support System (RLSS) based upon Space Station Freedom physicochemical technology. The paper describes the stepwise evolution of this baseline system into a closed-loop, Lunar base Controlled Ecological Life Support System (LCELSS), a hybrid design which incorporates both physicochemical and bioregenerative technologies. The steps taken in the evolutionary process are derived from a rationale which addresses: 1) the incorporation of specific bioregenerative functions into the life support system, 2) the supplementation of specific physicochemical functions with bioregenerative systems, 3) the replacement of initial physicochemical technologies with more advanced technologies, and 4) the addition of new physicochemical technologies. The rationale for location of the stages in the evolutionary development sequence is based upon considerations of mass requirements for human life support, on crew nutritional requirements, and on functional characteristics of the life support technologies.