In accordance with historical race concepts, Indonesian H. erectus subspecies were originally classified as the direct ancestors of Aboriginal Australians, but Solo Man is now thought to have no living descendants because the remains far predate modern human immigration into the area, which began roughly 55,000 to 50,000 years ago.

The Solo Man skull is oval-shaped in top view, with heavy brows, inflated cheekbones, and a prominent bar of bone wrapping around the back.

Solo Man likely inhabited an open woodland environment much cooler than present-day Java, along with elephants, tigers, wild cattle, water buffalo, tapirs, and hippopotamuses, among other megafauna.

They manufactured simple flakes and choppers (hand-held stone tools), and possibly spears or harpoons from bones, daggers from stingray stingers, as well as bolas or hammerstones from andesite.

Among these was German naturalist Ernst Haeckel who argued that the first human species (which he named "Homo primigenius") evolved on the now-disproven hypothetical continent "Lemuria" in what is now Southeast Asia, from a genus he termed "Pithecanthropus" ("ape-man").

Nevertheless, Haeckel's model inspired Dutch scientist Eugène Dubois to join the Royal Netherlands East Indies Army (KNIL) and search for his "missing link" in the Indonesian Archipelago.

[1]: 588 The "apeman of Java" nonetheless stirred up academic interest and, to find more remains, the Prussian Academy of Sciences in Berlin tasked German zoologist Emil Selenka with continuing the excavation of Trinil.

[2] From 1931 to 1933, 12 human skull pieces (including well-preserved skullcaps), as well as two right tibiae (shinbones), one of which was essentially complete, were recovered under the direction of Oppenoorth, ter Haar, and German-Dutch geologist Gustav Heinrich Ralph von Koenigswald.

At the same time, because of the Great Depression, the Survey's focus shifted to economically relevant geology, namely petroleum deposits, and the excavation of Ngandong ceased completely.

After much lobbying by Zwierzycki in the Survey, and after receiving funding from the Carnegie Institution for Science, von Koenigswald regained his position in 1937, but was too preoccupied with the Sangiran site to continue research at Ngandong.

[3]: 23–26 In 1935, the Solo Man remains were transported to Batavia (today, Jakarta, Java, Indonesia) in the care of local university professor Willem Alphonse Mijsberg, with the hope he would take over study of the specimens.

Jewish-German anthropologist Franz Weidenreich (who fled China before the Japanese invasion in 1941) arranged with the Rockefeller Foundation and The Viking Fund for von Koenigswald, his wife Luitgarde, and the Javan human remains (including Solo Man) to come to New York.

In 1978, von Koenigswald returned the material to Indonesia, and the Solo Man remains were moved to the Gadjah Mada University, Special Region of Yogyakarta (south-central Java).

The Survey's site map remained unpublished until 2010 (over 75 years later) and is of limited use now, so the taphonomy and geological age of Solo Man have been contentious matters.

Because of the sheer volume of fossils, humans and animals may have concentrated in great numbers in the valley upstream from the site due to the eruption or extreme drought.

[3] The dating attempts are: The racial classification of Aboriginal Australians, because of the robustness of the skull compared to that of other modern-day populations, has historically been a complicated question for European science since Johann Friedrich Blumenbach (the founder of physical anthropology) introduced the topic in 1795 in his De Generis Humani Varietate Nativa ("On the Natural History of Mankind").

[2] At the time, humans were generally believed to have originated in Central Asia, as championed primarily by American palaeontologist Henry Fairfield Osborn and his protégé William Diller Matthew.

They also rejected Raymond Dart's South African Taung child (Australopithecus africanus) as a human ancestor, favouring the hoax Piltdown Man from Britain.

Though Mayr later changed his opinion on the australopithecines (recognising Australopithecus), and a few species have since been named or regained some acceptance, his more conservative view of archaic human diversity became widely adopted in the subsequent decades.

[12]: 3 By the 1980s, as African species like A. africanus became widely accepted as human ancestors and race became less salient in anthropology, the Out of Africa theory overturned the Out of Asia and multiregional models.

[12]: 3 The date of 117 to 108 thousand years ago for Solo Man, predating modern human dispersal through Southeast Asia (and eventually into Australia), is at odds with this conclusion.

[18] The Solo Man remains are characterised by more derived traits than more archaic Javan H. erectus, most notably a larger brain size, an elevated cranial vault, reduced postorbital constriction, and less developed brow ridges.

Other Ngandong fauna include the tiger Panthera tigris soloensis, Malayan tapir, the hippo Hexaprotodon, sambar deer, water buffalo, the cow Bos palaesondaicus, pigs, and crab-eating macaque.

[23] The driest conditions probably corresponded to the glacial maximum roughly 135,000 years ago, exposing the Sunda shelf and connecting the major Indonesian islands to the continent.

If the date is correct for Solo Man, then they would represent a terminal population of H. erectus which sheltered in the last open-habitat refuges of East Asia before the rainforest takeover.

Weidenreich made note of anomalous inland stingray stingers at Ngandong, which he supposed were collected by Solo Man for use as daggers or arrowheads, similar to some recent South Pacific peoples.

[5]: 216–218  It is unclear if this apparent bone technology can be associated with Solo Man or later modern human activity,[23] though the Trinil H. e. erectus population seems to have worked with such material, manufacturing scrapers from Pseudodon shells and possibly opening them up with shark teeth.

[26] Traditionally, these have been interpreted as bolas (tied together in twos or threes and flung as a hunting weapon), but also individually thrown projectiles, club heads, or plant-processing or bone-breaking tools.

In 1993, American archaeologists Kathy Schick and Nicholas Toth demonstrated the spherical shape could be reproduced simply if the stone is used as a hammer for an extended period.

In 1972, Jacob alternatively suggested that because the base of the skull is weaker than the skullcap, and since the remains had been transported through a river with large stone and boulders, this was a purely natural phenomenon.