The species that are collectively known as the erectus grade are believed to be descendants of the African “erectus” form, Homo ergaster, which in turn is thought to be descended from one of the two species of early Homo, H. habilis or H. rudolfensis. They lived in one form or another from 1.8 mya to as recently as 25–17 kya. H. erectus was first discovered by Eugène Dubois in 1891 (see Figure 27.1), at the Trinil site on the Solo River in Java. He had gone to Asia to find evidence of human ancestors, since the popular notion at the time was that we originated there.
Title page from Dubois’s monograph. “Eugene Dubois, book” is in the public domain.
The first genus and species combination he assigned to the material was Anthropopithecus erectus (“upright man-ape”). He then changed it to Pithecanthropus erectus (“upright ape-man”). It was only later, after much more material had been unearthed, that Franz Weidenreich persuaded researchers that the species did not differ enough from our own to warrant different genus status. In more recent years, researchers have argued that the material from different continents should be assigned to different species. While we cannot know if the different continental assemblages represent true biological species, i.e. incapable of interbreeding, they are now minimally classified as geographic species. Since the holotype or “type specimen” came from Asia (Java), the species designation “erectus” was retained for Asian material. The African material has come to be known as H. ergaster, contemporary material from Dmanisi (in the Republic of Georgia) is known as H. georgicus, material from Spain as H. antecessor.
The strangely tiny and small-brained species from the island of Flores, Homo floresiensis, is thought to be a derived form of H. erectus. Some researchers place all of this material into the taxon H. erectus. Depending on which model people embrace for explaining the origin of our own species, one or more of those species would have evolved into archaic or premodern humans and, subsequently, anatomically modern humans (AMH), i.e. Homo sapiens sapiens. The Regional Continuity or Multiregional Model supposes that whatever erectus forms were present in the various locations evolved through a premodern form, often termed Archaic Homo sapiens whether neandertal-like or otherwise, and then into AMH via gene flow between the populations. However with the more widely accepted “Recent African Origin” (RAO) theory, which holds that our ancestors arose in Africa ~200 kya and then moved out to populate the rest of the world, those “erectus” species that did not contribute to our lineage went extinct. The problem remains as to which of the later “erectus” forms gave rise to our premodern form, Homo heidelbergensis. At this point in time, the most plausible choices for the origin of H. heidelbergensis, the ancestor of both Homo neanderthalensis and AMH, are Homo ergaster or Homo antecessor.