Solo Man (Homo erectus soloensis) is a subspecies of H. erectus that lived along the Solo River in Java, Indonesia, about 117,000 to 108,000 years ago in the Late Pleistocene. This population is the last known record of the species. It is known from 14 skullcaps, two tibiae, and a piece of the pelvis excavated near the village of Ngandong, and possibly three skulls from Sambungmacan and a skull from Ngawi depending on classification. The Ngandong site was first excavated from 1931 to 1933 under the direction of Willem Frederik Florus Oppenoorth, Carel ter Haar, and Gustav Heinrich Ralph von Koenigswald, but further study was set back by the Great Depression, World War II and the Indonesian War of Independence. In accordance with historical race concepts, Indonesian H. erectus subspecies were originally classified as the direct ancestors of Aboriginal Australians; however, Solo Man is now thought to have no living descendants as 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. The brain volume was quite large, measuring from , which is within the range of variation for present-day modern humans. One potentially female specimen may have been tall and weighed ; males were probably much bigger than females. Solo Man was in many ways similar to the Java Man (H. e. erectus) that had earlier inhabited Java, but was far less archaic.
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. They may have descended from or were at least closely related to Java Man. The Ngandong specimens likely died during a volcanic eruption. The species probably went extinct with the takeover of tropical rainforest and loss of preferred habitat, beginning by 125,000 years ago. The skulls sustained damage, but it is unclear if it resulted from an assault, cannibalism, the volcanic eruption, or the fossilisation process.
Research history Despite what English naturalist Charles Darwin had hypothesised in his 1871 book Descent of Man, many late-19th century evolutionary naturalists postulated that Asia, not Africa, was the birthplace of humankind as it is midway between Europe and America, providing optimal dispersal routes throughout the world (the Out of Asia theory). 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"). "Lemuria" had supposedly sunk below the Indian Ocean, so no fossils could be found to prove this. 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. On Java, he found a skullcap and a femur (Java Man) dating to the late Pliocene or early Pleistocene at the Trinil site along the Solo River, which he named "P." erectus (using Haeckel's hypothetical genus name) in 1893. He attempted unsuccessfully to convince the European scientific community that he had found an upright-walking ape-man. They largely dismissed his findings as a malformed non-human ape.
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. Following his death in 1907, excavation was carried out by his wife and fellow zoologist Margarethe Lenore Selenka. Among the members was Dutch geologist Willem Frederik Florus Oppenoorth. The yearlong expedition was unfruitful, but the Geological Survey of Java continued to sponsor the excavation along the Solo River. Some two decades later, the Survey funded several expeditions to update maps of the island. Oppenoorth was made the head of the Java Mapping Program in 1930. One of their missions was to firmly distinguish Tertiary and Quaternary deposits; among the relevant sites a bed dating to the Pleistocene discovered by Dutch geologist Carel ter Haar in 1931, downriver from the Trinil site, near the village of Ngandong.
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. Midway through excavation, Oppenoorth retired from the Survey and returned to the Netherlands, replaced by Polish geologist in 1933. 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. In 1934, ter Haar published important summaries of the Ngandong operations before contracting tuberculosis. He returned to the Netherlands and died two years later. Von Koenigswald, who was hired principally to study Javan mammals, was fired in 1934. 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.
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. Before he had the opportunity, the fossils were moved to Bandung, West Java in 1942 because of the Japanese occupation of the Dutch East Indies. Japanese forces interned von Koenigswald for 32 months. At the cessation of the war, he was released, but the Indonesian War of Independence erupted. 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. Von Koenigswald and Weidenreich studied the material at the American Museum of Natural History until Weidenreich's death in 1948 (leaving behind a monograph on Solo Man posthumously published in 1951). In his 1956 book Meeting Prehistoric Men, von Koenigswald included a 14-page account of the Ngandong project with several unpublished results. The Solo Man remains came to be stored at Utrecht University, the Netherlands. In 1967, von Koenigswald gave the material to Teuku Jacob for his doctoral research. Jacob oversaw the excavation of Ngandong from 1976 to 1978 and recovered two more skull specimens and a pelvic fragment. 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 specimens are: Skull I, an almost complete skullcap probably belonging to an elderly female; Skull II, a frontal bone probably belonging to a three to seven-year-old child; Skull III, a warped skullcap probably belonging to an elderly individual; Skull IV, a skullcap probably belonging to a middle-aged female; Skull V, a probable male skullcap—indicated by its great length of ; Skull VI, an almost complete skullcap probably belonging to an adult female; Skull VII, a right parietal bone fragment probably belonging to a young, possibly female, individual; Skull VIII, both parietal bones (separated) possibly belonging to a young male; Skull IX, a skullcap missing the base probably belonging to an elderly individual (the small size is consistent with a female, but the heaviness is consistent with a male); Skull X, a shattered skullcap probably belonging to a robust elderly female; Skull XI, a nearly complete skullcap; Tibia A, a few fragments of the shaft, measuring in diameter at the mid-shaft, probably belonging to an adult male; Tibia B, a nearly complete right tibia measuring in length at in diameter at the mid-shaft, probably belonging to an adult female; Ngandong 15, a partial skullcap; Ngandong 16, a left parietal fragment; and Ngandong 17, a left acetabulum (on the pelvis which forms part of the hip joint).
Age and taphonomy The location of these fossils in the Solo terrace at the time of discovery was poorly documented. Oppenoorth, ter Haar, and von Koenigswald were only on site for 24 days of the 27 months of operation as they needed to oversee other Tertiary sites for the Survey. They left their geological assistants — Samsi and Panudju — to oversee the dig; their records are now lost. 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. All 14 specimens were reported to have been found in the upper section of Layer II (of six layers), which is a -thick stratum with gravelly sand and volcaniclastic hypersthene andesite. They are thought to have been deposited at around the same time, probably in a now-dry arm of the Solo River, about above the modern river. The site is about above sea level.
Volcaniclastic rock indicates deposition occurred soon after a volcanic eruption. 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. The ash would have poisoned the vegetation, or at least impeded its growth, leading to starvation and death among herbivores and humans, accumulating a mass of carcasses decomposing over several months. A lack of carnivore damage may indicate sufficient feeding was possible without having to resort to crunching through the bone. When the monsoon season came, lahars streaming from the volcano through the river channels swept the carcasses to the Ngandong site, where they and other debris created a jam because of the channel narrowing there. The H. erectus fossils from Sambungmacan, also along the Solo River, were possibly deposited in the same event.
The dating attempts are: In 1932, based on the site's height above the present-day river, Oppenoorth suggested Solo Man dated to the Eemian interglacial, which at the time was roughly constrained to 150 to 100 thousand years ago from the Middle/Late Pleistocene transition. Later biochronological studies (using the animal remains to constrain the age) within the next few years by Oppenoorth in 1932, von Koenigswald in 1934, and ter Haar in 1936 agreed with a Late Pleistocene date. The Solo Man remains were first radiometrically dated in 1988 and again in 1989, using uranium–thorium dating, to 200 to 30 thousand years ago, a wide error range. In 1996, Solo Man teeth were dated, using electron spin resonance dating (ESR) and uranium–thorium isotope-ratio mass spectrometry, to 53.3 to 27 thousand years ago; this would mean Solo Man outlasted continental H. erectus by at minimum 250,000 years and was contemporaneous with modern humans in Southeast Asia, who immigrated roughly 55 to 50 thousand years ago. In 2008, gamma spectroscopy on three of the skulls showed they experienced uranium leaching, and the Solo Man remains were re-dated to roughly 70 to 40 thousand years ago. This would still make it possible Solo Man was contemporaneous with modern humans.