I think this behavior is learned rather than inherited. Benthic zone is sometimes filled with vegetation, so stickleback fish could always hide there. On the other hand, marine zone lacks vegetation, they were taught by their territory that schooling in groups is the only way to protect themselves from predators. As a result, they were able to school twice the mean time the benthic stickleback fish could perform. It would be much easier for the enemy to chase down a single fish than chasing down a bunch of them. The benthic stickleback fish were not taught this method; they are used to hide between vegetation until they feel safe.
