They may like to move it...

...but the question is, how? Some biogeography news that might shed some light on the whole Madagascar-moving issue.

The island subcontinent, which has had some pretty good PR recently, is the proud owner of one of the most unique faunas on the planet. In fact, the world's fifth-largest island, which lies just 300 miles of the coast of southeast Africa, has more endemic animals than any other location with the exception of the much larger island continent of Australia. The most famous of the island's inhabitants are the high profile, photogenic lemurs, but almost 90% of the other amphibians, reptiles, and mammals are found nowhere else.

The animals of Madagascar had to come from somewhere. The island has been isolated for over 100 million years - vertebrate life has been there for less than 65 million. Historically, two competing ideas have suggested different mechanisms for the intial inoculation of the island's fauna - a land bridge which would allow for overland movement or an overseas "sweepstakes" dispersal explanation which envisions ancestral Madagascarians (my word) rafting their way on floating debris.

Each of the ideas has its problems. There's no geological evidence of a land bridge connection between Madagascar and the African continent, and our knowledge of plate tectonics doesn't allow for a drifting continent connection. Furthermore, a land bridge connection would allow for a fairly nonselective introduction of species to the island - large animals like lions and hippos and giraffes in addition to the smaller ones that form the bulk of Madagascar's fauna. On the other hand, the rafting hypothesis is complicated by the fact that existing ocean currents flow in the wrong direction to faciliate an easy drift across the Mozambique Channel.

In a new paper in Nature, Purdue's Matthew Huber and Jason Ali of the University of Hong Kong report the results of computer simulations indicating that ancient ocean currents would have made the rafting possibility much more likely. Huber's simulations, performed on a supercomputer at Purdue and employing information about climate patterns 20 million to 60 million years ago, indicate that currents at the time likely flowed east - toward Madagascar from Africa. Furthermore, they would have likely been strong, fast currents, enabling a small reptile or mammal swept to sea on a raft of floating vegetation to make the shores of Madagascar without starving or dying of thirst.

In biogeography, distribution explanations employing this type of sweepstakes dispersal are sometimes met with skepticism. They are, after all, sort of a wild card. Can't explain a distribution pattern any other way? Then they must have floated there. Modeling techniques such as these may make it easier for us to provide some supporting evidence.