Modern humans evolved in Africa. However, our ancestors didn't stick around and soon spread around the globe. Boats helped in this. However, we weren't the first hominin species to leave Africa. Homo erectus and others left before us. Did they also use boats during their migration?
This has been debated for a long time. It would imply a huge degree of manufacturing skill, planning, and knowledge about the world. Might it require more intelligence than we think these earlier species had?
There is some circumstantial evidence in favour of it. For instance, some of the earliest European fossils found are in Spain. A leap straight from Africa to Spain would require boats, given the ocean in the way Or maybe there are fossils from a Eastern land route we just haven't found yet.
However, a growing body of evidence from Greek islands is providing more solid evidence for pre-human sea voyages. Stone tools from Crete, Cyprus, and other Mediterranean islands seem to predate the emergence of humans. This would be seemingly conclusive proof pre-human species were using boats.
Before the Minotaur there were rocks
Homo erectus first left Africa ~1.8 million years ago. That's almost 1.6 million years before modern humans have even evolved, let along begun thinking about leaving our homeland.
Despite the head start Homo erectus didn't make it as far as us. They seem to have been constrained by the ocean, not making into the New World or onto any Pacific islands. In fact, they didn't even make it very far into Europe for quite a while. The first evidence of hominins there doesn't appear for another half a million years. Even then, these initial occupations are rare and sporadic; with few sites in places like Italy and Spain.
It takes another few hundred thousand years for the hominin population in Europe to expand significantly. By that point it doesn't even look much like Homo erectus any more. These Europeans seem to have evolved into (or perhaps been replaced by migrations from elsewhere) Homo antecessor. This group would eventually go onto evolve into (or again, be replaced by) Homo heidelbergensis, who definitely did evolve into the Neanderthals.
All of which is very confusing, with lots of latin names to remember. So for simplicity, I'm just going to be calling them all pre-humans. Because they were living in Europe before modern humans arrived there. A lot easier to remember.
Anyhoo, whilst all of this inter-species faffing about was going on; some of these pre-humans managed to get onto several Greek islands (most notably Crete). This was during a glacial period, so sea levels were lower as a lot of water was locked up in the ice. But despite this these islands would still have been islands. Boats would have been required for the journey.
Possible ancient boats
How could these pre-human individuals made this voyage? Although the distance would have been relatively short - thanks to the lower sea levels - such coastal voyages are often more dangerous. Rocks, cliffs, and currents all present a hazard.
We know these individuals were smart and had access to some decent technology. This includes some excellent woodworking skills, as evidenced by the Schonningen spears. These were straightened, sharpened and tempered. Clearly, these people weren't incompetent. Yet their boats were clearly sub par as they were unable to make the same spread to Australia and the New World that humans later did.
So researchers have been investigating what sort of travel options would have been available to these pre-human Europeans, given what we know about these technical skills. Some of them are depicted below.
These options require varying levels of technology. How far along were these pre-human species? Impossible to say. However, even some of the more basic designs could have made the voyage. In fact, they still can. Recreations of simple cane rafts have crossed to Crete in just 48 hours. Given the reduced distances during the ice age, the pre-human species could have made the journey in a fraction of the time using this sort of basic technology.
Speaking of reduced distances, that was one of the big advantages these early mariners would have had. The shorter distances involved means that Crete and the other islands they travelled to would always have been visible. A bountiful land of opportunity visible on their doorstep.
Some other possible ways they could have planned their voyage have been proposed. Perhaps they used a stone age map, a rather interesting (possible) example of which has been found. However, it was found associated with humans, not pre-humans. So I don't think we can assume they would also have been making maps.
Sinking the boat
All of this sounds fairly promising. However, it is also fairly circumstantial. It hinges upon the reliability of the pre-human finds from the Greek islands. Without that evidence this all becomes barely justified speculation.
And sadly that evidence isn't as strong as most people would like. In most cases it's very scarce, making it difficult to reliably date. For example, Cyprus contains some possible pre-human tools, along with many human tools. But only the latter have been securely dated (to around 11,000 years ago). Were the other tools actually pre-human? No way of knowing for sure without actual dates. After all, humans are known to have made "old fashioned" technology.
But that's not to say there is no evidence for pre-human occupation. Tools from Crete have been found that can be much more reliably dated to pre-human times (around 130,000 years ago). Tools there have been found embedded in rocks securely dated to 107,000 years ago. So we can't pin down exactly when they were made (and thus which of the many pre-human species made them). But this date would make them older than any human habitation of Europe.
Yet even this good evidence is rather small in quantity. This leads me to suspect that there probably wasn't any long term habitation of these islands. Maybe the pre-humans got their accidentally, blown off course whilst fishing. Maybe the boat was smashed and they died there. Or perhaps they only visited occasionally. I'm sure you don't need my help speculating wildly about what was going on here.
But this low quantity of tools does raise the possibility that boats weren't involved in the journey. Might currents or storms have carried a handful of objects from the mainland to the islands. Maybe a few individuals went along with them by accident. It's known to happen to other species, often being "rafted" during a storm to another island. Yet whilst the evidence for pre-humans on these islands is scarce, I suspect it's too common to be accounted for by this sort of stuff.
I'm fairly convinced there was a pre-human Boaty McBoatface; but more work is needed to know for sure.
tl;dr
Early hominins made their way to Greek islands. They would have needed boats to get there. Sadly, everything beyond these facts is speculation.
References
Finlayson, C., 2005. Biogeography and evolution of the genus Homo. Trends in Ecology & Evolution, 20(8), pp.457-463.
Howitt-Marshall, D. and Runnels, C., 2016. Middle Pleistocene sea-crossings in the eastern Mediterranean?. Journal of Anthropological Archaeology, 42, pp.140-153.
Strasser, T.F., Runnels, C., Wegmann, K., Panagopoulou, E., Mccoy, F., Digregorio, C., Karkanas, P. and Thompson, N., 2011. Dating Palaeolithic sites in southwestern Crete, Greece. Journal of Quaternary Science, 26(5), pp.553-560.
