  We have simulated the evolution of age structured populations whose
individuals represented by their diploid genomes were distributed on a square
lattice. The environmental conditions on the whole territory changed
simultaneously in the same way by switching on or off some requirements.
Mutations accumulated in the genes dispensable during a given period of time
were neutral, but they could cause a genetic death of individuals if the
environment required their functions again. Populations survived due to
retaining some surplus of genetic information in the individual genomes. The
changes of the environment caused the fluctuations of the population size.
Since the simulations were performed with individuals spatially distributed on
the lattice and the maximal distance between mating partners was set as a
parameter of the model, the inbreeding coefficient in populations changed
unevenly, following the fluctuation of population size and enhancing the
speciation phenomena.
