I have a species which is about half the size of a human. They live on a continent composed of large islands. I'm looking at their migration history.
The thing is, I'm likely to have the origin of the mutations that make them intelligent on a small island. Now this island is about 20 to 30 km away from any other landmass, be it other islands or the rest of the continent (which is large islands over 1000km across).
The question is: for a species that's developing intelligence, if it's half the size of humans and somewhere on the evolution track approximately at the same level as early Australopithecus, how far could it travel over water? Would a raft be able to carry it across those 20 km? Would it depend on currents? And would enough individuals be able to make it across to start new populations on the other side of the sea?
I know there are theories of Homo Erectus crossing large bodies of water on rafts, even some thinking Habilis might have done it, but as far as I can tell, Australopithecus was stuck in Africa and here I'm not sure if they'd escape their small island, let alone the larger one that is over 2000 km across.