One of the 'themes' you need to think about, when studying human evolution, is dispersal – just how did human populations spread about the globe, and when did they do it? In September this year a group of scientists got to together to talk about how and when humans might have become seafarers.
It turns out there is considerable debate among scientists, about both the timing of humans setting out (whether on rafts or boats) and the degree to which this was purposeful (as opposed to people being accidentally swept out to sea on a raft of floating vegetation, for example). Messing about in boats has been very important in the spread of different civilisations around the world, and yet we can't be absolutely certain when and where humans first took to the water.
Boats – logs that have been laboriously hollowed out by hand – have been found in France and the Netherlands, and date back to around 10,000 years ago. And people began living on Cyprus, in the Mediterranean, around 12,000 BP, and must have used boats to get there. However, the fact that humans arrived in Australia at least 45,000 years ago, across a substantial stretch of open sea, suggests that our ancestors must have come up with the concept of boats (or rafts) at least that long ago. By 28,000 years ago they had made the 180 km crossing to Buka, in the Solomon Islands, though we have no way of knowing whether this involved paddling or the use of sails – there's no evidence of sails until 20,000 years later.
But whether rafting, or in something more like a boat – did those ancient mariners deliberately venture out to sea, or was it an accidental journey?
M. Balter (2007) In search of the world's most ancient mariners. Science 318: 388-389