In this paper we analyze the role of environmental
variations in the evolution of artificial agents situated in an
external environment. By comparing the results of experiments
carried out in different conditions we demonstrate how
environmental variations promote the evolution of better
solutions. The beneficial effect is maximized at intermediate rates
of variations, i.e. when the dynamics of the environment displays
a sufficient level of stability and variability. The advantage of
intermediate rates of variation is due to the fact that the
occurrence of new environmental conditions favors the retention
of phenotypic variations that can eventually provide an advantage
also in different environmental conditions. Moreover, a relative
stability of the new environmental conditions constitutes a
prerequisite for the generation and retention of such variations.
