This phenomenon could not be detected through traditional dietary research methods, but by using DNA-based techniques, such interactions were revealed for the first time, leading to important questions about how human activities affect wildlife.

The local authorities in Japan subsequently conducted a DNA survey of all the monkeys in the zoo and confirmed that 57 of the 167 monkeys were hybrids of macaques crossed with a specific exotic creature, the rhesus macaque, accounting for about one-third of the monkey population

Species invasions are actually a very common occurrence on a global scale. Although there are countless species of organisms on the planet, these are distributed all over the world, with some species being endemic to certain areas and not present in others, and others having a relatively wide distribution. When some species appear in places where they would not have previously existed, this is when the species may become invasive.