And Then Came Clothing and Speech - Mark Roberts discusses why Europe was colonized by hominids half a million years ago. This was originally published in the Journal of British Archaeology in 1996.
Roberts argues that colonists were more advanced than what researchers had previously thought. He also notes that these hominids were displaying many behaviors consistent with modern humans.
From the site:
Why was Europe colonised by hominids half a million years ago? And what sort of people were these first colonisers?
There may be evidence, as some claim, for a sporadic occupation of Spain around a million years ago at sites such as Atapuerca and Orce (see BA, September 1995). However, without doubt the main colonising event began in the interglacial, or warm period, of 524-478,000 years ago. During this period incontestable sites are found throughout the western part of the continent. The originators of this colonis-ing thrust are thought to have come from Africa and the Levant, and their principal tool was the stone handaxe. They are referred to generally as archaic modern humans or specifically as Homo cf heidelbergensis, although some researchers still see them as Homo erectus rather than an evolved form of this lineage.
As for why these hominids moved into Europe, hypotheses have been postulated such as a change in the composition of the carnivore populations of Europe, thus reducing competition for food resources; or climatic and hence environmental change in Africa, forcing a general population movement. It is feasible that these populations met up with other colonisers coming from the east via Asia and the Caucasus.
But what forces were driving the colonisers steadily northwards and east? The archaeological record suggests it was unlikely to be because of competition with a remnant population, or population pressure amongst the colonisers. One explanation may be recolonisation of the continent by flora and fauna, as the inter-glacial climate began to take effect - hominids may well have moved in conjunction with expanding ecological zones that satisfied their subsistence requirements. There exists too, the possibility that the migration route may have been around the European coastline, which would have avoided many of the natural obstacles of a direct route, although access to large grazing herds would have been restricted.