In the year 2000 in the Republic of Georgia, two human skulls were found that date back to 1.7 million years ago. These fossils have been classified as Homo ergaster, which many scientists think is the African version of Homo erectus. This find shocked the scientific world, who had previously thought Homo erectus's journey out of Africa was due to their advancing tool technology that dated back to 1.4 million years ago. But the finds in Georgia prove that these hominids were on the move even earlier than we thought, and more importantly, that they journeyed this distance without the help of advanced tools. Other finds, such as an Erectus in java, and a possible Homo habilis in China have called into question the traditional theory that Erectus originated and evolved in Africa.
Before the Georgian fossil finds, it was believed that their Acheulean tool industry was most responsible for their survival out of Africa. But the skulls in Georgia predate the Acheulean tool industry by over a quarter million years. And whats more, these hominids were recovered alongside about 1,000 simpler stone tools from the Olduvai tradition. So not only were they out of Africa far earlier than anyone knew, they got there with a simple tool technology. Such discoveries have shattered commonly held theories about the evolution of human ancestors and have led others to propose new theories as to why they may have left Africa when they did. These theories better explain how it could have been possible for such a primitive version of Homo erectus might've found itself in foreign parts of the world.
One possibility is that the Erectus may have originated earlier in Africa than we think, and that we just haven't found their oldest fossils yet. This might have delayed their journey out of Africa just long enough to exploit the area of its resources before moving on. In order to support this type of theory, it would be important to find in Africa Erectus fossils that predate those already discovered. These finds would have to be distinguishable enough to make certain they are of the species Erectus. They would need the longer arms, narrower hips, and cone shaped ribcage that sets them apart from the Homo Habilis species. The perfect find would be an intact skull showing a cranial capacity well beyond the Habilis average. But even if such fossils are found, they still wouldn't solve the riddle as to why they left Africa in the first place.
In answering this question most now believe that instead of tool technology pushing them across new terrains, it was their changing biology. The Homo erectus living in Georgia were not privy to Acheulean tools because they werent invented until hundreds of thousands of years later. The Erectus was growing a bigger body and brain. In order to maintain it, protein was needed and meat became an important part of their diets. The Erectus, therefore, needed to exploit their environment for meat to fuel their ever increasing brain size and body. Meat was soon to run out in Africa due to the high population concentrated on one continent, and it wasn't long before some Erectus moved out. In doing so, they were lessening tensions between themselves and the other African animals, and they were expanding their diets to include more meat from different areas of the earth. Climate may have also played a part, however probably not as important a factor as biology.
In order to support such theories, it would be important to find fossils of other Erectus living outside of Africa dating back as far as these. This would indicate that these weren't the only two of the species Erectus that left Africa. Another important find would be even older fossils further away from Africa, indicating that some Erectus were on the move and got even further than Georgia. But I think the most important kind of find supporting this theory would be relating to their primitive tool technology. If indeed they left Africa to eat more meat, animal bones should also be present at the site. An article in Archaeology Online lists animals whose bones were discovered at the Georgia site. I think further study of these animal bones should investigate whether or not they are marked with tool marks and whether or not these marks were done in hunting or scavenging. This would be important because evidence on the bones of being hunted and not scavenged would indicate that Erectus had followed the animals out of Africa. The list on the website includes animals that today are only found in the African savannah. This indicates that Erectus may have been familiar with the animals from Africa before they left. In this case, its probable that they might have left Africa with the animals.
This brings up interesting questions about the climate at the time. The article says that the Black Sea region was once warmer and more dry than it is today. If this area of the world was indeed as warm as believed, it would have been the perfect place to escape in search for more meat. So then it's possible that both biology and climate led the Erectus out of Africa and into other areas of the world, not the advanced tool industry as was believed before. If this turns out to be true, it's much to Homo Erectus's credit. They survived a lengthy travel several thousands of years before we even thought it was possible. And they did so without the help of advanced tools. Perhaps they should be an inspiration to us all, braving the conditions with only what we have, on a path to insure our own survival.