Population trajectories for accidental versus planned colonisation of islands.

We modify an existing model of the population trajectory on an island after the first arrival of a group of hominins to compare the potential success rates of accidental arrival (e.g., on vegetation rafts following major floods or a tsunami) against planned colonisation by watercraft. Our model predicts that colonisation through the accidental arrival of a group of individuals on an island should be around half as likely to be successful as colonisation through the arrival of a planned voyaging party of the same size, but that this difference could be entirely counteracted by the infrequent arrival of small numbers of individuals by similar accidental circumstances in the centuries after the initial colonisation. We argue that our model investigations strengthen the plausibility that especially early island colonisation (such as Homo erectus on Flores) may have occurred as a result of highly anomalous natural events (such as a tsunami), and thus hominin colonisation of islands outside swimming range of continents should not be seen as necessarily indicating the existences of seafaring technologies and skills.