Richard Collins: Sizing up life on an island

The Island Rule states that species living on islands tend to become either bigger or smaller, depending on the resources available

The remains of a Giant Irish deer at the Natural History Museum in Dublin. Picture: Haydn West

In Through the Looking-Glass, Alice participates in ‘the Red Queen’s race’. To stay in the same place on the chessboard, she has to keep running constantly. The Red Queen Hypothesis says that, like Alice, a species can’t rest on its evolutionary laurels; its survival depends on keeping abreast of developments taking place among co-evolving predators, prey and rivals.

Leigh Van Valen, the Chicago-based biologist who formulated the hypothesis, invented two related ones. According to his Law of Extinction, the likelihood of a species going to the wall is not related to how long the species has been in existence. His Island Rule, proposed in 1973, has been much debated; members of species living on islands tend to become either bigger or smaller, depending on the resources available.