Although, as we discussed earlier, there is no real definition of the term 'human', for me, Homo erectus/ergaster is the first real 'human'species. They seem to represent a major step forward in the origin of modern humans. They look far more modern than any earlier species; their brain size is close to or within the range of ours, they have a very modern stature (remember, the Nariokotome boy might have reached 6 feet in height, while Homo habilis and rudolfensis were still very short), they have modern looking teeth, and they began to make relatively elaborate stone tools, especially their Acheulian handaxes. Would you agree with this or do you find that you have a different idea of the concept of 'human'?
Regardless of this question, Homo erectus/ergaster was the first of our ancestors to learn to adapt to a much broader range of conditions beyond those found in Africa. When they moved into Europe and Asia, they would have encountered much cooler environments and very different types of plants and animals, and yet they appear to have adapted quite readily to these changes. This ability to adapt very quickly to new conditions without significant changes in physiology (remember Homo erectus was already Homo erectus before they left their Africa homeland) became the hallmark of humans and is only possible with the aid of culture. Homo erectus/ergaster used technology and changes in social structure to survive in the new regions they came to inhabit.