  Emergence of one-time-direction macroscopic evolution of a classical system
of two mixed gases having different temperatures is derived and explained.
  The analysis performed at the microscopic level, where the time-symmetric
laws of mechanics govern the particles collisions, leads to a time-asymmetric
macroscopic heat transfer equation and a theorem analogous to the Boltzmann
H-theorem. Some statistical symmetries in the velocity distribution that should
be satisfied by the incoming and outgoing particles are pointed out. The time
reversed evolution is shown to be highly improbable because in this case these
typical symmetries are broken. Additionally, some remarks explaining implicit
time-asymmetry of the Boltzmann \emph{Stosszahlansatz} are made.
