First, based on the extensive quantum mechanics in biology, Schrödinger equation at column coordinates and its solution may derive the double helical structure of DNA. It is necessity mathematical conclusion that quantum mechanics has symmetry. Second, we discuss the nonlinear biomechanics, which is related to chaos, fractal and soliton, etc. Third, an important character of the nonlinear biosystems is the formation of self-organization, which should decrease entropy. Fourth, we propose the preliminary epidemic equations of COVID-19, and discuss their meaning. Complex biology provides a wide region for entropy decrease in various isolated systems.

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First, Darwinian evolution and mutual help seem to conflict. Second, since the second law of thermodynamics is based on isolated-equilibrium systems, it is in fact very limited. But, in essence, the vast majority of systems in the universe and nature are constantly changing and evolving with “life”. We proposed possible entropy decrease in isolated system due to internal interactions, etc. Based on biophysics, we research coevolution from thermodynamics and entropy by unified method. Let the entropy change dSA of a subsystem A is a set of its elements dSi , which may have various internal interactions with cooperation and complementary each other, so entropy may be decrease. This corresponds to the principle of least action of entropy change. It includes self evolution, and competition each other, etc. Third, evolution may combine self-optimization and selforganization, etc. Brain control of the body is the most typical of an internal interaction. No one would think that this only leads to an entropy increase. Fourth, we discuss the biological synergetics, ecosystem, and sustainable development. The cooperation-competition is a common phenomenon in the ecosystem. Coevolution is the more general evolution-development law of biological and active systems. This can unify natural competition and mutual help in biology, and is an important model for human development direction.