Abstract  Even the chemical component of the first life was found, it would not be the essence of life. This gap in understanding is not only a technological neglect, but also an absence of a main concept — positive feedback. All the existent definitions of life have obvious faults, including the Theory of Life as Metabolism, Supple Adaptation, Information and the Heredity. Modern system theories, including the Dissipative Structure Theory and the Hypercycle Theory, have not provided a precise definition of life, either. Self-reproduction is the essential characteristic which is owned by all creatures and not by all non-living things. The premise of evolution of creatures is the survival of their complex structures. The reason of the survival of complex structures is the index increasing of the number of creatures. The reason of index increasing is self-reproduction. Self-reproduction can solve the probability problem of the emerge of complex structure. The definition of life: Life 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. The ability to make its complex structure survive by its own properties is vitality. Research of artificial life inspires us that it is possible for life to exist without material like carbon, hydrogen and oxygen.

Keywords  Philosophy of science and technology, origin of life, system science, self-reproduction, positive feed- back

Ⅰ. The Essence of Life and a Main Concept

The origin of life is not only a scientific problem, but also a philosophical problem. It is one of the four origin problems which should be answered in the 21^st century. Although scientists have been able to obtain all genetic maps of human being and other creatures, this is not enough to really understand life. It is knowing hows but not the whys. Most scientists still research the origin of life from chemical component, especially complex organics with carbon. Even the chemical component of the first life was found, it would not be the essence of life. After a chemical way of the origin of life have been found, the second, third and forth ways should be searched continually. The generality of these ways is the essence of life. This gap in understanding is not only a technological neglect, but also an absence of a main concept, this concept is positive feedback.

Ⅱ. Disadvantages of Existent Definitions of Life

The definition of life is related with the origin of life, both of which rely on the the understanding of life. At present, there are two kinds of definitions of life, one is the Definition by Function, which defines life by its properties and functions, and the other is the Structural Definition (or the Entity Definition), which defines life by special structure of life. There are two kinds of the Definition by Function, one is the Cluster Definition which regards life as an assemblage of many properties, and the other is the Root Property Definition, which consider one or a few properties as the essential property of life (Li, 2002, p.24-39). All of these definitions have obvious disadvantages.