The RNA world hypothesis is regarded as an acceptable hypothesis drawing the early stage of a simple chemical network system to a primitive life-like system. However, details how the RNA-based life-like system had begun on the primitive Earth are not understood. Continuous consideration of the bio-systematic view of life-like systems at different hierarchical levels by our group led to both the model of time-dependent development of life-like systems and the two-gene hypothesis on the origin-of-life. The two-gene hypothesis provides an insight into the mechanism of the simple chemical network system to a life-like system, which involves both the controlling information and the metabolic systems regarding the informational molecules. The history on the development of the two-gene hypothesis and a prospect regarding the two-gene hypothesis will be briefly discussed.