‘Island Rule’ Evolution Theory Challenged

British scientists are questioning a theory concerning the evolution of giant rodents, miniature elephants and even miniature humans on islands.

The Imperial College London researchers are challenging the island rule theory that says in island environments small mammals, such as rodents, tend to evolve to be larger, and large mammals, such as elephants, tend to evolve to be smaller, with the original size of the species being the key determining factor in the changes.

The new research suggests the tendency to either evolve larger or smaller on islands varies from one group of species to another, regardless of original size.

If the island rule was correct, then most large mammals living on islands would be smaller than their continental relatives, and most small island mammals would be larger those living on continents, said Shai Meiri, lead author of the research. Our large dataset of mammal body sizes shows that this isn’t the case: there is evidence that most mammal groups show no tendency to consistently either grow larger or smaller, in contradiction to the island rule.

The study appears in the Proceedings of the Royal Society B: Biological Sciences.