Computer simulations of chromosomes' and genomes' evolution suggest that the genes located on relatively large and densely packed chromosomes should be grouped in clusters. Clusters located on homologous chromosomes may complement their defects or they may co-operate providing selective advantage to their hosts. Since recombination inside clusters is harmful, selection leads to the uneven distribution of recombination events along chromosomes - relatively high recombination in the subtelomeric regions and low recombination in the central regions of chromosomes. Uneven distribution of recombinations enables sympatric speciation which can not be predicted by the mean field theories of evolution. Further studies of chromosome evolution require more precise data (the best ? full sequences) of many closely related genomes belonging to the same species.