To interpret the various fossils relevant to the evolution of the Genus Homo, and eventually our species H. sapiens, you need to keep in mind two major hypotheses about human evolution. At the present, it is fair to say neither is entirely proven, though the evidence is increasingly stonger for the Replacement Hypothesis. From what you know already, all of the story of human evolution is "out of Africa". The ancestors of the genus Homo are to be found among the Australopithecines, and quite possibly Ardipithecus. All of these forms evolved in Africa, yet modern humans are found all over the world. Clearly the ancestors of most modern humans left Africa at some point; the question is, when? Or perhaps phrased differently, how many times did hominins leave Africa, and were all of them the ancestors of modern humans?
aka. "Out of Africa"; "Noah's Ark" or the "Eve Theory"
The replacement hypothesis says that there were probably three hominin migrations out of Africa, but only the last one involved populations of Homo sapiens who eventually became the ancestors of modern non-Africans (and of course of modern Africans). According to this hypothesis, H.sapiens evolved in Africa, and eventually moved out of Africa to replace hominin populations living in Asia and Europe.
The first major migration out of Africa took place shortly after 2 mya, when early Homo (Homo ergaster, evolving into Homo erectus) moved into southwestern Asia, and eventually into much of southern Asia and Europe. These were tool making, culture-bearing hominins, and they went on to evolve in ways which made them quite distinct both physically and culturally in different regions. They populated much of Asia and perhaps some of Europe, but did not expand into the Americas, Australia, or the Pacific Islands.
The second migration out of Africa was of a more evolved hominin, (Homo heidelbergensis) one that evolved in Africa and moved into southwest Asia and into Europe some 500,000 ya or more. Once there, he evolved into Homo neanderthalensis by about 150,000 years ago.
The third and final major migration out of Africa took place around 100,000 years ago, when anatomically modern Homo sapiens, having evolved in Africa from H.heidelbergensis, moved into Asia and Europe, slowly replacing (without mating with) the earlier populations of Homo erectus and Homo neanderthalensis. Eventually, more recently than 60,000 years ago, Homo sapiens migrated into Australia and the Americas, and much later, the Pacific Islands.
The specific evidence for the replacement hypothesis will be discussed later. This model obviously correlates well with punctuated equilibrium, the hypothesis that states that human evolution is a series of bushes, lots of "experiments" being thrown out by natural selection, with only one surviving to evolve. And that one species could evolve into another bush with several species or branches, with only one branch evolving into modern humans.
If the replacement hypothesis is totally valid, than we are going to be briefly discussing a couple of fossils that are definitely not our ancestors. In my view, the fossil evidence, the archaeological evidence, and the mtDNA evidence currently strongly support the replacement hypothesis, though with a minor qualification to be discussed in a later lesson. The replacement hypothesis is the one presented in the Phylogeny lesson. Your text barely mentions either hypothesis, but in my view their presentation of fossils is so simplistic as to be erroneous. (However, their presentation of the cultural developments is excellent, and one I do not cover well in my lessons! Depend on the lessons for physical evolution, and be sure to also read the text for cultural developments.)
aka. Multiregional Evolution, Multiregionalism, or the Candelabra Model
The regional continuity hypothesis reflects the older model of human evolution, though that does not necessarily make it wrong. (However, once again, the evidence increasingly does not support regional continuity.) In this model early Homo (usually considered to be Homo erectus) migrated out of Africa by 2 million years ago, occupying Asia and eventually Europe. In this hypothesis, this was the only migration. The subsequent evolution into Homo sapiens happened more or less separately in Africa, Asia, and Europe. This means that those who had the most complex brains, the best ability to communicate, etc., were selected for in Africa, in Asia, and in Europe. Although there may well have been some gene flow between neighboring groups, and even various large scale migrations, Homo sapiens evolved more or less simultaneously and independently on each of the three continents. Later, after 60,000 years ago, people spread from eastern Asia into Australia, the Americas, and finally the Pacific, as indicated by all evidence.
The model correlates well with early views of human evolution as a straight line of fossils, with each species gradually evolving into a more modern looking, and acting, form. In this view, specific fossils such as Homo erectus in east Asia, and Homo neanderthalensis in southwest Asia and Europe, of ancestral to the populations living there. Even your text does not agree with this interpretaion of the Neandertals.
While probably more paleoanthropologists today believe that the replacement hypothesis has more evidence supporting it, there are others that vehemently believe that evidence supporting regional continuity is either being ignored, or misinterpreted. Again, I do not believe that is the case, but if you are interested, you can certainly do your own research.