  The identical ideal individual hypothesis is proposed. According to this
hypothesis, the identical ideal individuals should be classified into two
classes: the bosonic individuals and the fermionic individuals. The bosonic
individuals can occupy the same behavior state while the fermionic individuals
can not be in the same behavior state. We propose that human beings and many
species of animals are fermionic, which can not occupy the same behavior state
according to the Pauli exclusion principle. An unified theoretical explanation
is given for the natures of two important and seemingly irrelated phenomena in
psychology: the existence of the personal space and the behavior
differentiation under high population density condition.
