Although biology has achieved great successes in recent years, we have not got a clear idea on "what is life?" Actually, as explained here, the main reason for this situation is that there are two completely distinct aspects for "life", which are usually talked about together. Indeed, in respect to these two aspects: Darwinian evolution and self-sustaining, we must split the concept of life correspondingly, for example, by defining "life form" and "living entity", separately. For life's implementation (related to the two aspects) in nature, three mechanisms are crucial: the replication of DNA/RNA-like polymers by residue-pairing, the sequence-dependent folding of RNA/protein-like polymers engendering special functions, and the assembly of phospholipid-like amphiphiles forming vesicles. The notion "information" is significant for us to comprehend life phenomenon: the life form of a living entity can just be defined by its genetic information; Darwinian evolution is essentially an evolution of such information, transferred across generations. The in-depth analysis concerning the essence of life would improve our cognition in the whole field of biology, and may have a direct influence on its subfields like the origin of life, artificial life and astrobiology.
Reviewers: This article was reviewed by Anthony Poole and Thomas Dandekar.
Keywords: Bioinformation; Darwinian entity; Origins of life; Self-sustained system; The definition of life.