Solo Man (Homo erectus soloensis) is a subspecies of H. erectus that lived near the Solo River in Java, Indonesia, between about 117,000 and 108,000 years ago during the Late Pleistocene. This group is the last known record of the species. Scientists have found 14 skullcaps, two shin bones, and a piece of the pelvis near the village of Ngandong. Some researchers also believe three skulls from Sambungmacan and one from Ngawi may belong to Solo Man, depending on how the remains are classified. The Ngandong site was first studied from 1931 to 1933 by scientists Willem Frederik Florus Oppenoorth, Carel ter Haar, and Gustav Heinrich Ralph von Koenigswald. However, further research was delayed due to the Great Depression, World War II, and the Indonesian War of Independence. In the past, Indonesian H. erectus subspecies were thought to be direct ancestors of Aboriginal Australians, but now Solo Man is believed to have no living descendants because the remains are much older than when modern humans arrived in the region, which was about 55,000 to 50,000 years ago.
The Solo Man skull is oval-shaped when viewed from above, with thick brow ridges, large cheekbones, and a strong ridge of bone around the back. The brain size was large, ranging from 1,013 to 1,251 cubic centimeters (61.8 to 76.3 cubic inches), similar to modern humans. One possibly female specimen may have been 158 cm (5 feet 2 inches) tall and weighed 51 kg (112 pounds), while males were likely larger. Solo Man shared many traits with Java Man (H. e. erectus), but had more modern features.
Solo Man likely lived in cooler open woodland areas, alongside elephants, tigers, wild cattle, water buffalo, tapirs, and hippos. They used simple stone tools such as flakes and choppers, and may have made spears or harpoons from bones, daggers from stingray stingers, and bolas or hammerstones from andesite. They may have descended from or been closely related to Java Man. The Ngandong remains may have died during a volcanic eruption. The species likely became extinct as tropical rainforests expanded and their preferred habitat was lost, beginning around 125,000 years ago. The skulls show damage, but the cause is unclear—it may have resulted from an attack, cannibalism, the volcanic eruption, or the fossilization process.
Research history
Even though Charles Darwin suggested in his 1871 book Descent of Man that humans originated in Africa, many scientists in the late 1800s believed Asia was the birthplace of humankind because it was located between Europe and America, making it easier for humans to spread around the world (the Out of Asia theory). One of these scientists was German naturalist Ernst Haeckel, who claimed the first human species, which he called Homo primigenius, evolved on a now-disproven landmass called "Lemuria" in what is now Southeast Asia. He believed this landmass had sunk beneath the Indian Ocean, which is why no fossils could be found to support his idea. Despite this, Haeckel’s theory inspired Dutch scientist Eugène Dubois to join the Royal Netherlands East Indies Army (KNIL) and search for evidence of the "missing link" between apes and humans in the Indonesian Archipelago. On the island of Java, Dubois discovered a skullcap and a femur (later called Java Man) near the Solo River in 1893. He named the bones Pithecanthropus erectus (using Haeckel’s genus name) and tried to convince European scientists that he had found a human-like ape that walked upright. However, most scientists dismissed his findings, believing the bones came from a deformed ape, not a human ancestor.
The discovery of Java Man sparked interest among scientists, and the Prussian Academy of Sciences in Berlin asked German zoologist Emil Selenka to continue excavations at the Trinil site. After Selenka’s death in 1907, his wife, Margarethe Lenore Selenka, and Dutch geologist Willem Frederik Florus Oppenoorth continued the work. Although their yearlong expedition found no new remains, the Geological Survey of Java continued funding excavations along the Solo River. In the 1930s, the Survey supported mapping projects on Java, and Oppenoorth became the head of the Java Mapping Program in 1930. One of their goals was to identify layers of rock from the Pleistocene era, including a site discovered by Dutch geologist Carel ter Haar in 1931 near the village of Ngandong, downriver from Trinil.
Between 1931 and 1933, 12 human skull pieces (including well-preserved skullcaps) and two right tibiae (shinbones) were found at Ngandong under the direction of Oppenoorth, ter Haar, and German-Dutch geologist Gustav Heinrich Ralph von Koenigswald. Oppenoorth left the Survey in 1933 and was replaced by Polish geologist Józef Zwierzycki. At the same time, the Great Depression shifted the Survey’s focus to economically valuable geology, such as petroleum, and excavations at Ngandong stopped. In 1934, ter Haar published summaries of Ngandong’s findings before falling ill with tuberculosis and returning to the Netherlands, where he died in 1936. Von Koenigswald, hired to study Javan mammals, was fired in 1934 but returned to the Survey in 1937 with help from the Carnegie Institution for Science. However, he focused on the Sangiran site and did not continue work at Ngandong.
In 1935, the Solo Man remains were moved to Batavia (now Jakarta, Indonesia) for study by local professor Willem Alphonse Mijsberg. Before this could happen, the fossils were relocated to Bandung, West Java, in 1942 due to the Japanese occupation of the Dutch East Indies. Japanese forces imprisoned von Koenigswald for 32 months. After the war, he was released, but the Indonesian War of Independence began. Jewish-German anthropologist Franz Weidenreich, who had fled China before the Japanese invasion, arranged for von Koenigswald, his wife, and the fossils to move to New York with help from the Rockefeller Foundation and The Viking Fund. Von Koenigswald and Weidenreich studied the remains at the American Museum of Natural History until Weidenreich’s death in 1948, after which a monograph on Solo Man was published in 1951. In his 1956 book Meeting Prehistoric Men, von Koenigswald included a detailed account of the Ngandong project. The fossils were later stored at Utrecht University in the Netherlands. In 1967, von Koenigswald gave the material to Teuku Jacob for his doctoral research. Jacob excavated Ngandong from 1976 to 1978, finding two more skulls and a pelvic fragment. In 1978, von Koenigswald returned the fossils to Indonesia, and the Solo Man remains were moved to Gadjah Mada University in Yogyakarta, Java.
Age and taphonomy
The location of these fossils in the Solo terrace when they were discovered was not well recorded. Oppenoorth, ter Haar, and von Koenigswald were only at the site for 24 days during the 27 months of the project because they had to manage other Tertiary sites for the Survey. They left their geological assistants, Samsi and Panudju, to manage the excavation; however, the records they made are now lost. The Survey’s site map was not published until 2010 (over 75 years later) and is not very useful today. This has made it difficult to determine the taphonomy and geological age of Solo Man. All 14 fossils were reported to be found in the top part of Layer II (one of six layers), which is a 46 cm (18 in) thick layer of gravelly sand and volcaniclastic hypersthene andesite. These fossils are believed to have been deposited around the same time, likely in a now-dry branch of the Solo River, about 20 m (66 ft) above the modern river. The site is located about 40 m (130 ft) above sea level.
Volcaniclastic rock suggests that the fossils were deposited soon after a volcanic eruption. Because of the large number of fossils, humans and animals may have gathered in large numbers in the valley upstream from the site due to the eruption or a severe drought. The volcanic ash likely made it hard for plants to grow, leading to starvation and death among herbivores and humans, causing many bodies to pile up and decompose over several months. The lack of damage from carnivores may indicate that food was available without the need to eat bones. When the monsoon season arrived, lahars (mudflows) from the volcano traveled through the river channels and carried the dead animals and other debris to the Ngandong site. There, the debris and carcasses created a blockage because the river channel narrowed. The H. erectus fossils from Sambungmacan, also along the Solo River, may have been deposited during the same event.
The dating attempts are:
Classification
The way scientists have classified Aboriginal Australians has been a complex topic for European researchers since Johann Friedrich Blumenbach, who started the study of physical anthropology, introduced the idea in 1795 in his work On the Natural History of Mankind. After Charles Darwin proposed the theory of evolution, Thomas Henry Huxley suggested in 1863 that European Neanderthals and Aboriginal Australians might share a common ancestor. This idea was later supported by other scientists until the discovery of ancient humans in Indonesia.
In 1932, a scientist named Oppenoorth compared the Solo Man skull to the Rhodesian Man from Africa, Neanderthals, and modern Aboriginal Australians. At the time, many scientists believed humans originated in Central Asia, a view promoted by Henry Fairfield Osborn and his student William Diller Matthew. They argued that the rise of the Himalayas and Tibet forced early humans to walk upright. They also claimed that populations in tropical regions, like Java Man and the "Negroid race," regressed over time. These scientists rejected Raymond Dart’s discovery of the Taung child (Australopithecus africanus) as a human ancestor and instead supported the Piltdown Man hoax.
Oppenoorth initially thought the Ngandong fossils represented a type of Neanderthal related to Rhodesian Man and named them Javanthropus soloensis. However, he later changed the name to Homo (Javanthropus) soloensis after comparing them to the Wajak Man. He believed Java Man evolved in Indonesia and became the ancestor of modern Aboriginal Australians, with Solo Man as a transitional fossil. He also grouped Rhodesian Man with this lineage. Oppenoorth thought Chinese Peking Man (now Homo erectus pekinensis) spread westward and gave rise to Neanderthals.
These early classifications grouped Java Man, Solo Man, and Rhodesian Man into the "Pithecanthropoid-Australoid" lineage, which included Aboriginal Australians and Melanesians. This idea was part of the multiregional origin theory, supported by scientists like Weidenreich and Carleton S. Coon. They believed modern human races evolved separately from local archaic human species. Aboriginal Australians were seen as the most "primitive" race alive.
In the 1950s, Ernst Mayr, a German biologist, simplified human classification by defining only three Homo species: H. transvaalensis (australopithecines), H. erectus (including Solo Man and other groups), and Homo sapiens (modern humans and Neanderthals). He viewed them as a sequence of evolving species. Though Mayr later revised his views on australopithecines, his approach influenced later research.
Later scientists classified Solo Man as a subspecies of H. erectus, placing it in the "Neanderthal/Neanderthaloid" group, which included transitional fossils between H. erectus and H. sapiens. In the 1960s and 1970s, Australian anthropologist Alan Thorne suggested Aboriginal Australians arrived in two waves: one with robust features from H. erectus and another with more gracile features from modern East Asians. However, later research showed some robust fossils were younger than the gracile ones.
By the 1980s, the "Out of Africa" theory replaced earlier models, as African fossils like Australopithecus africanus were widely accepted as human ancestors. The multiregional model was revised to suggest that archaic humans in different regions interbred with modern humans. Solo Man may have hybridized with modern ancestors of Aboriginal Australians traveling through Southeast Asia. This idea, called the assimilation model, was not universally accepted.
In 2006, Steve Webb proposed that Solo Man was the first human species to reach Australia, with robust modern Australians being hybrid populations. However, Solo Man’s age (117 to 108,000 years) predates modern human migration to Southeast Asia, leaving no living descendants. A 2021 study of 400 modern human genomes found no evidence of interbreeding with H. erectus.
Solo Man is generally thought to descend from Java Man (H. erectus), with fossils from Sambungmacan and Ngawi classified as H. erectus soloensis or transitional forms. It is unclear if there was gene flow from other regions. An alternate theory, proposed in 1973, suggests that Sangiran/Trinil and Ngandong/Ngawi/Sambungmacan populations evolved separately. If correct, this could classify Solo Man as a distinct species (H. soloensis), though scientific definitions of species and subspecies remain unclear.
Anatomy
The identification of whether a fossil is from an adult or juvenile H. erectus was based on the closure of the cranial sutures, which are the seams between the bones of the skull. Scientists assumed these sutures closed at a rate similar to modern humans, though they may have closed earlier in H. erectus. The skull of Solo Man is much thicker than that of modern humans, with thickness ranging from double to triple the average. Male and female specimens were distinguished by assuming males were more robust than females, though both were exceptionally strong compared to other Asian H. erectus. Adult skulls average 202 mm × 152 mm (8.0 in × 6.0 in) in length and breadth, and are proportionally similar to Peking Man but have a larger circumference. Skull V is the longest, measuring 221 mm (8.7 in). For comparison, modern human skulls average 176 mm × 145 mm (6.9 in × 5.7 in) for men and 171 mm × 140 mm (6.7 in × 5.5 in) for women.
The Solo Man remains show more advanced traits than older Javan H. erectus, including a larger brain size, a higher cranial vault, less narrowing near the eyes, and less pronounced brow ridges. They still closely resemble earlier H. erectus. Like Peking Man, a slight ridge runs across the top of the skull. Compared to other Asian H. erectus, the forehead is proportionally low and has a shallow angle. The brow ridges curve downward in the middle, forming a nasal bridge, and are thick, especially at the sides. Like Peking Man, the frontal sinuses are located between the eyes rather than extending into the brow area. Compared to Neanderthals and modern humans, the area where the temporal muscle would attach is flat. The brow ridges merge into thick cheekbones. The skull is phenozygous, meaning the skullcap is narrow compared to the cheekbones, making the cheekbones visible from above. The triangular shape of the temporal bone and the sharp infratemporal crest are similar to Peking Man. The inferior and superior temporal lines on the parietal bone diverge toward the back of the skull, like in earlier Javan H. erectus.
At the back of the skull, a sharp, thick bone ridge called the occipital torus separates the occipital and nuchal planes. This ridge is most prominent where the external occipital protuberance would be in modern humans. The base of the temporal bone matches Java Man and Peking Man rather than Neanderthals or modern humans. Unlike Neanderthals and modern humans, a bony pyramid is present near the root of the pterygoid bone. The mastoid part of the temporal bone juts out. The occipital condyles (bones connecting the skull to the spine) are smaller compared to the foramen magnum (the opening where the spinal cord enters the skull). Large, irregular bony projections are located behind the occipital condyles.
Brain volumes of six Ngandong H. erectus specimens range from 1,013 to 1,251 cc (61.8 to 76.3 cu in). The Ngawi I skull measures 1,000 cc (61 cu in), and the three Sambungmacan skulls measure 1,035, 917, and 1,006 cc (63.2, 56.0, and 61.4 cu in), averaging over 1,000 cc (61 cu in). Asian H. erectus typically have brain volumes averaging about 1,000 cc (61 cu in). For comparison, a 1955 study of 63 Aboriginal Australians found brain volumes ranging from 943 to 1,399 cc (57.5 to 85.4 cu in), meaning H. erectus brain sizes fall within the modern human range. The base of the braincase and brain appear flat rather than curved. The sella turcica, a structure near the pituitary gland, is much larger than in modern humans. In 1951, Weidenreich suggested this might be due to an enlarged gland that caused thickened bones.
Of the two known tibiae (shin bones), Tibia A is more robust than Tibia B and resembles Neanderthal tibiae. Like other H. erectus, the tibiae are thick and heavy. Based on a reconstructed length of 380 mm (15 in), Tibia B may have belonged to a 158 cm (5 ft 2 in) tall, 51 kg (112 lb) individual. Tibia A likely belonged to a larger individual. Asian H. erectus height estimates (based on a small sample) range from 150–160 cm (4 ft 11 in – 5 ft 3 in), with Indonesian H. erectus in tropical areas generally taller than continental specimens in colder regions. The single pelvic fragment from Ngandong has not been formally described.
Culture
At the species level, the Ngandong fauna is similar to the older Kedung Brubus fauna from about 800 to 700 thousand years ago. This was a time when many large mammal species, such as Asian elephants and Stegodon, moved to Java. Other animals found at Ngandong include the tiger Panthera tigris soloensis, Malayan tapir, hippo Hexaprotodon, sambar deer, water buffalo, cow Bos palaesondaicus, pigs, and crab-eating macaques. These animals suggest an open woodland environment. The presence of a common crane at the nearby Watualang site might mean the climate was much cooler than today. The driest conditions, around 135,000 years ago, likely exposed the Sunda shelf, connecting major Indonesian islands to the continent. By 125,000 years ago, the climate became wetter, making Java an island and allowing tropical rainforests to grow. This change led to the replacement of Ngandong fauna by the Punung fauna, which represents modern-day animals on Java. However, Punung animals like orangutans and gibbons probably could not reach Java until the island was reconnected to the continent after 80,000 years ago. Homo erectus, which lived in woodlands and savannahs, likely went extinct as open habitats disappeared.
Homo erectus soloensis was the last group of Homo erectus on Java, living there from 1.51 to 0.93 million years ago at the Sangiran site, 540 to 430 thousand years ago at the Trinil site, and 117 to 108 thousand years ago at Ngandong. If the dating of Solo Man is correct, they may have been the final population of Homo erectus surviving in the last open areas of East Asia before rainforests spread. Before modern humans arrived, Late Pleistocene Southeast Asia also had Homo floresiensis on Flores, Indonesia, and Homo luzonensis on Luzon, the Philippines. Genetic studies show that Denisovans (a group known only through DNA) were widespread in Southeast Asia and interbred with early modern humans about 45.7 and 29.8 thousand years ago. A 2021 study suggests modern humans did not interbreed with Denisovans or other endemic human species, unless their offspring did not survive.
Many Homo erectus soloensis bones were found at Ngandong, suggesting a large population before a volcanic eruption buried them. However, it is hard to estimate the exact population size. The Ngandong site was far from the northern coast, but the location of the southern shoreline and the mouth of the Solo River is unclear.
In 1936, archaeologist Oppenoorth studied photos of Ngandong bones and noticed damage to a tiger skull and deer antlers, which he thought showed evidence of bone tools. He suggested some antlers had carved bird skulls attached for use as axes. In 1951, Weidenreich doubted this, arguing that river currents and animals like crocodiles might have caused the damage. Oppenoorth also thought a carved bone with a wavy pattern was a harpoon, but Weidenreich believed it was a spearhead. Weidenreich noted unusual stingray stingers at Ngandong, which he thought were used as weapons, similar to tools used by some South Pacific peoples. It is unclear if these items were made by Homo erectus or later humans. Earlier Homo erectus at Trinil may have used shells and shark teeth to make tools.
Oppenoorth also found a round andesite stone ball at Ngandong, a common item in the Solo Valley. Similar balls have been found in European and African sites, including the Acheulean of Kenya. These balls were once thought to be hunting tools like bolas or club heads, but in 1993, researchers showed that repeated use as a hammer could create their shape.
In 1938, von Koenigswald and others collected stone tools from Ngandong, but river damage made it hard to identify them. The tools were small, simple, and mostly made of chalcedony, chert, or jasper. Some volcanic rocks and wood fragments were modified into heavy tools. A 1973 find at Sambungmacan included a unifacial chopper made of andesite. Because so few tools were found, it is hard to classify Homo erectus at Ngandong into a specific tool-making tradition. Unlike Acheulean sites in Africa and Eurasia, Ngandong lacks complex tools like hand axes. In 1948, Movius suggested this was due to differences in environment between western and eastern Homo erectus (the "Movius Line"), as open areas allowed big-game hunting.
Though the "Movius Line" is no longer widely accepted, hand axes are still rare in East Asia. Possible reasons include differences in raw materials, use of bamboo instead of stone, or lower population density.
In 1951, Weidenreich and von Koenigswald noted serious injuries on Skulls IV and VI, likely caused by a sharp object and a blunt object. These injuries showed signs of healing, meaning the individuals survived. Only skullcaps were found, with no teeth, which is unusual. They concluded that these skulls were likely victims of an attack that did not succeed.