  Previous evolutionary studies demonstrated how evaluating evolving agents in
variable environmental conditions enable them to develop solutions that are
robust to environmental variation. We demonstrate how the robustness of the
agents can be further improved by exposing them also to environmental
variations throughout generations. These two types of environmental variations
play partially distinct roles as demonstrated by the fact that agents evolved
in environments that do not vary throughout generations display lower
performance than agents evolved in varying environments independently from the
amount of environmental variation experienced during evaluation. Moreover, our
results demonstrate that performance increases when the amount of variations
introduced during agents evaluation and the rate at which the environment
varies throughout generations are moderate. This is explained by the fact that
the probability to retain genetic variations, including non-neutral variations
that alter the behavior of the agents, increases when the environment varies
throughout generations but also when new environmental conditions persist over
time long enough to enable genetic accommodation.
