Abstract: Organisms exhibit diverse responses when exposed to novel environments, and successful adaptation depends on aligning evolutionary histories with these new conditions. Reusing standing genetic variation is a critical mechanism for this adaptation process. Using an extended Fisher's geometric model, we conducted simulations of evolving populations to investigate how evolutionary histories influence adaptation to novel environments. Our results highlight that distinct evolutionary histories produce varying patterns of genetic variance within populations. When organisms return to previously experienced environments, they exhibit enhanced performance and rapid adaptation. This supports the validity of the strategy commonly employed in ecological restoration to revert habitats to their original state. Moreover, small deviations of the greatest genetic variance direction from the optimum are beneficial for both fitness and fitness increase. A small genetic variance size is advantageous for fitness but impedes fitness increase. A short distance to the optimum and a sharp genetic variance shape are beneficial for fitness but have no significant effects on fitness increase. Our findings underscore the crucial role of evolutionary histories in shaping genetic variance and evolutionary potential when adapting to a new optimum. These results contribute to an evolutionary understanding of the factors underlying the disparate responses of phenotypically similar species to environmental change.

Key words: direction of greatest genetic variance, evolutionary trajectories, individual based simulations, rapid environment change.