Anything which meets these conditions is life by all means, no matter whether it is constituted by protein or nuclear acid or other materials, no matter whether it transfers information for other life process, even no matter whether it is capable of metabolism.

Self-reproduction needs many conditions, maybe including certain materials, temperature, humidity, pressure, etc. But these conditions are not considered here in the sufficient conditions of the origin of life. If a system is able to self-reproduce, it has already had these conditions.

Self-reproduction includes simple self-reproduction and self-reproduction with characteristic of hypercycle. Self-reproductions in all of existent creatures need to be catalyzed by proteins which come from the translation of RNA. Hence all of these self-reproductions have charac- teristic of hypercycle.

The first life is called Luca. There must had been a lot of very complex non-living things before Luca occur. Complex things are difficult to emerge and easy to break. Though the world has trend of automatic evolution, the achievement of evolution cannot survive if its speed to emerge is smaller than the speed to break. Therefore, those complex non-living things cannot be seen by human. This would never have changed without self-reproduction. Hence, self-reproduction is the necessary condition of life origin. It is self-reproduction that makes it possible for complex structure to break the prison of the Second Law of Thermodynamics.

Creatures have many properties, including metabolism, growth, heredity, evolution and reflection, but not all kinds of creatures have all these properties. Self- reproduction in nature is the only property possessed by all creatures. The simplest creature can live without metabolism and growth, but cannot live without breeding.

Theorem: The necessary conditions of the origin of life is:

l A kind of material has relatively complex structure.

l It is able to self-reproduce in nature.

l This kind of structure is fit for some certain environment, i.e., it can make an index increasing of its number.

Therefore, these conditions are sufficient and necessary conditions of the origin of any life.

Openness, fluctuation, variation and natural selection are also necessary conditions of the origin of life, but they are not rare resources and are not considered here.

Bedau said, “To surmount the notorious difficulties of defining life, we should evaluate theories of life not by whether they provide necessary and sufficient conditions for our current preconceptions about life but by how well they explain living phenomena and how satisfactorily they resolve puzzles about life” (Bedau, 1998). But, if the real necessary and sufficient conditions for life are found, we shall be able to explain living phenomena and resolve puzzles about life in the easiest way. What is more, it is easy to deduce the definition of life after knowing the sufficient and necessary conditions of life origin.

Definition: Living substance is a kind of relatively steady and complex system with special structure, the structure enables it to have the function of making its structure survive in nature by self-reproduction and other positive feedback.