Every pursuit system follows a kind of evolutionism: pursuer's pursued quantity is decided by its adaptive behaviors in environment. In this article, I shall discuss the micro-mechanism for biological evolution and some minimum conditions for a pursuit system to develop.

Biology evolution is also a developing process for cells, although very slow compared with human beings' life-span. It is result of cells, or even more basic elements, pursuing their best states.

A cell has ability to choose what to input from environment, although the ability is imperfect: can not prevent some harmful matter from coming inside. A cell also has ability to choose what to output, although the ability is imperfect too: can not output matter to cells at all possible states. A cell has ability to move toward a better state, although the ability is very weak. For an imperfect pursuit system, if behaviors are averagely good enough, the pursuit system can develop, although it can not develop the best.

For two cells, if one's output is wanted by the other, it is similar to mutual attraction. Cells tend to be close with each other, similar to gravity.

Environment, like body fluid, is similar to market. Exchange between two cells includes three steps: a cell outputs a matter, the matter flows in environment, the matter will be absorbed by another cell. Similarly in universe, each interaction includes three steps: a charge outputs field, field propagates in space, field inputs by charge.

Above is the micro-mechanism for biology evolution, from unicellular life to human beings. Reproduction and heredity just keep number of cells to increase, or to offset death, an imperfect property for cells, at least.

From my discussion about universe, society, research and biology evolution, the following four conditions are necessary conditions for a pursuit system to develop from competition and reciprocation:

--pursuer has some right and ability to choose what to input, what to output and where to move;

--some pursuers want to input some of the other pursuers' output;

--there is one or several market to store pursuers' output, from which pursuers choose what to input;

--pursuers and market must have some stability. In universe, it means charge and potential can not change too quickly¡ªslower than light velocity.