n is from ape.
The development of human life has been associated with four paleontological periods known as the Quaternary Hominidae, with the first or basal Quaternary starting at a maximum of 3 million and a minimum of 1 million years ago. Later periods are known as the Early Quaternary (1 million to 400,000 years ago); Middle Quaternary (400,000 to 100,000 years ago); and Late Quaternary (100,000 to 10,000 years ago) ("Human life," 1981, pp. 211-212). Hominids of the basal and Early Quaternaries, which include examples of Homo erectus, were not "culture-bearing" creatures in the modern meaning of the term (Robinson, 1981, p. 439). However, they do appear to have been rational, as indicated by evidence of toolmaking and food-storage survival strategies (Robinson, 1981, passim; "Human life," 1981). In this regard, Sagan says that the bipedal morphology of Homo erectus freed the hands and suited the species to toolmaking tasks (1980, p. 284).
Competing human-development theories collide in three principal areas of interpretation: morphological/fossil features; extent and nature of culture-bearing/rational characteristics; and geographical/geochronological features. Interpretation, taxonomy, and theory overlap and converge in all three areas. Equally significant, as Robinson explains, is the fact that the whole field of human development is difficult and "in some respects must remain speculative." Accordingly, he says, "considerable difference of opinion may always exist and absolute certainty will always be impossible" (Robinson, 1981, p. 440). There is apparently no evidence that successive human species (i.e., species and subspecies) were "sympatric," or occupying the same territory at the same time. In other words, physical or mental differentiation perforce implied separation.
Robinson describes the earliest human species as Australopithecus africanus, a 3 million-year-old specimen discovered by Raymond Dart in 1...