Indian mongooses were introduced to Japan’s Amami island in 1979 to control the rat and pit viper populations. They also preyed on the tip-nosed frog, dramatically reducing their numbers. Once the mongooses were removed, the population of the frogs rebounded. A recent project found that, when approached by researchers, frogs in areas where the impact of the mongooses had been greatest would hop away faster than those in less affected areas. Since almost all of the mongooses were removed from the island five years ago, it is unlikely that the frogs observed have ever seen one, and so this cannot have been learned from contact with mongooses. The greater wariness in the frogs must have been caused by a genetic change.