  We show, that the specific distribution of gene's length, which is observed
in natural genomes, might be a result of a growth process, in which a single
length scale $L(t)$ develops that grows with time as $t^{1/3}$. This length
scale could be associated with the length of the longest gene in an evolving
genome. The growth kinetics of the genes resembles the one observed in physical
systems with conserved ordered parameter. We show, that in genome this
conservation is guaranteed by compositional compensation along DNA strands of
the purine-like trends introduced by genes. The presented mathematical model is
the modified Bak-Sneppen model of critical self-organization applied to the
one-dimensional system of $N$ spins. The spins take discrete values, which
represent gene's length.
