Solo Man (Homo erectus soloensis) is a type of Homo 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. Fossils include 14 skull caps, two tibiae, and a piece of the pelvis found near Ngandong village. Some scientists also believe three skulls from Sambungmacan and a skull from Ngawi may belong to Solo Man, depending on how the fossils are classified. The Ngandong site was first studied between 1931 and 1933 by Willem Frederik Florus Oppenoorth, Carel ter Haar, and Gustav Heinrich Ralph von Koenigswald. Further research was delayed due to the Great Depression, World War II, and the Indonesian War of Independence.
In the past, Indonesian Homo erectus subspecies, including Solo Man, were first thought to be the direct ancestors of Aboriginal Australians. However, Solo Man is now believed to have no living descendants because their remains are much older than when modern humans arrived in the region, which was about 55,000 to 50,000 years ago.
Solo Man skulls are oval-shaped when viewed from above, with thick brow ridges, large cheekbones, and a strong bone bar around the back. Their brain size ranged from 1,013 to 1,251 cubic centimeters, similar to modern humans. One possibly female specimen may have been 158 cm (5 ft 2 in) tall and weighed 51 kg (112 lb). Males were likely much larger than females. Solo Man shared many traits with Java Man (Homo erectus erectus), but had more modern features.
Solo Man likely lived in a cooler, open woodland environment with animals such as elephants, tigers, wild cattle, water buffalo, tapirs, and hippos. They made simple stone tools like flakes and choppers, and may have used bones for spears or harpoons, stingray stingers for daggers, and andesite for bolas or hammerstones. They may have descended from or been closely related to Java Man. The Ngandong fossils likely died during a volcanic eruption. The species probably went extinct as tropical rainforests spread and their preferred habitat was lost, beginning around 125,000 years ago. Damage to the skulls is unclear, but it may have resulted from an attack, cannibalism, the eruption, or the fossilization process.
Research history
In 1871, English naturalist Charles Darwin suggested that humans evolved from earlier species. However, many scientists in the late 1800s believed that Asia, not Africa, was where humans first appeared. They thought Asia’s location between Europe and America made it easier for early humans to spread across the world (called the "Out of Asia" theory). German naturalist Ernst Haeckel supported this idea. He claimed the first human species, which he called "Homo primigenius," evolved on a landmass named "Lemuria" in what is now Southeast Asia. He believed this landmass, which was later shown not to exist, sank beneath the Indian Ocean, making it impossible to find fossils. Haeckel’s theory inspired Dutch scientist Eugène Dubois to search for evidence of early humans in Indonesia. On the island of Java, Dubois found a skullcap and a femur (called "Java Man") near the Solo River in 1893. He named the bones "P. erectus" after Haeckel’s idea. Dubois struggled to convince European scientists that these bones belonged to an upright-walking "ape-man." Most scientists dismissed his findings as belonging to a non-human ape.
Despite this, the discovery of "Java Man" sparked interest. The Prussian Academy of Sciences in Berlin asked German zoologist Emil Selenka to continue digging 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. Their search for more remains was not successful, but the Geological Survey of Java continued to fund excavations along the Solo River. In the 1930s, the Survey funded mapping projects on Java, and Oppenoorth became the head of the Java Mapping Program in 1930. His team, including Dutch geologist Carel ter Haar, identified a Pleistocene-era site near the village of Ngandong in 1931.
Between 1931 and 1933, 12 human skull pieces and two shinbones were found at Ngandong under the leadership 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 important geology, like oil, and excavations at Ngandong stopped. In 1934, ter Haar published summaries of the Ngandong project before falling ill with tuberculosis and dying in 1936. Von Koenigswald, who was hired to study Javan mammals, was fired in 1934. With help from Zwierzycki and the Carnegie Institution for Science, von Koenigswald returned to his work in 1937 but focused on the Sangiran site instead of Ngandong.
In 1935, the Ngandong fossils were moved to Batavia (now Jakarta, Indonesia) for study by local professor Willem Alphonse Mijsberg. However, during the Japanese occupation of the Dutch East Indies in 1942, the fossils were moved to Bandung, West Java. Japanese forces imprisoned von Koenigswald for 32 months. After World War II ended, von Koenigswald 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 Ngandong fossils to move to New York with funding from the Rockefeller Foundation and The Viking Fund. Von Koenigswald and Weidenreich studied the fossils at the American Museum of Natural History until Weidenreich’s death in 1948. Weidenreich left behind a written study on the Ngandong fossils, published in 1951. In his 1956 book Meeting Prehistoric Men, von Koenigswald included details about the Ngandong project. The fossils were later stored at Utrecht University in the Netherlands. In 1967, von Koenigswald gave the fossils to Teuku Jacob for his research. Jacob led excavations at Ngandong from 1976 to 1978, finding two more skulls and a bone from the pelvis. In 1978, von Koenigswald returned the fossils to Indonesia, where they were moved to Gadjah Mada University in Yogyakarta, Java.
Age and taphonomy
The location of these fossils in the Solo terrace when they were found 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 assistants, Samsi and Panudju, to supervise the dig, but 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 helpful 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 upper 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 part 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 shortly after a volcanic eruption. Because there are so many fossils, humans and animals may have gathered in large numbers upstream from the site due to the eruption or a severe drought. Volcanic ash could have harmed plant life or stopped it from growing, causing herbivores and humans to starve and die. Their bodies may have decomposed over several months. The lack of signs from carnivores eating bones might mean that animals had enough food and did not 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 debris to the Ngandong site. There, the accumulation of debris blocked the river channel. Fossils of H. erectus from Sambungmacan, also along the Solo River, may have been deposited during the same event.
The dating attempts are:
Classification
The classification of Aboriginal Australians by European scientists has been a complex topic since Johann Friedrich Blumenbach introduced the idea in 1795 in his book On the Natural History of Mankind. After Charles Darwin's theory of evolution was introduced, Thomas Henry Huxley proposed 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, Oppenoorth compared the Solo Man skull to those of Rhodesian Man from Africa, Neanderthals, and modern Aboriginal Australians. At the time, many scientists believed humans originated in Central Asia, as argued by Henry Fairfield Osborn and William Diller Matthew. They claimed the rising Himalayas and Tibet forced early humans to walk on two legs. They also believed populations in tropical regions, like Java Man and the "Negroid race," regressed over time, a theory called "degeneration." 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 first thought the Ngandong fossils represented a type of Neanderthal related to Rhodesian Man and named them Javanthropus soloensis. Later, he renamed them 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 humans—Java Man, Solo Man, and Rhodesian Man—were often grouped 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 Coon. They believed modern human races evolved separately from local archaic humans. Aboriginal Australians were considered the most "primitive" race alive.
In the 1950s, Ernst Mayr simplified human classification, defining only three Homo species: H. transvaalensis (australopithecines), H. erectus (including Solo Man), and Homo sapiens (modern humans and Neanderthals). He viewed them as a sequence of species evolving one after another. Though Mayr later recognized Australopithecus as a separate group, his approach influenced later research.
Later scientists classified Solo Man as a subspecies of H. erectus, placing it in the "Neanderthal/Neanderthaloid group" as a transitional form between H. erectus and Homo sapiens. In the 1960s and 1970s, Australian anthropologist Alan Thorne proposed that Aboriginal Australians arrived in two waves: one with robust features from H. erectus, and another with more gracile features from East Asian ancestors. However, later studies showed the 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 interbred with modern humans in their regions, a theory called the "assimilation model." Solo Man may have interbred with early modern humans traveling to Australia. However, this idea was not universally accepted.
In 2006, Steve Webb suggested Solo Man might have been the first human species to reach Australia, with modern Australian fossils showing hybrid ancestry. However, Solo Man's age (117–108,000 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 Homo erectus.
Solo Man is generally considered to have descended from Java Man (H. erectus), with fossils from Sambungmacan and Ngawi classified as H. erectus soloensis or an intermediate stage. It is unclear if there was gene flow from other regions. An alternative theory, proposed in 1973, suggests that Sangiran/Trinil and Ngandong/Ngawi/Sambungmacan populations evolved separately. If correct, this might classify Solo Man as a distinct species (H. soloensis). However, definitions of species and subspecies in paleoanthropology remain unclear.
Anatomy
Scientists determined if a skull was from an adult or juvenile by looking at how the cranial sutures closed, assuming they 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 up to three times greater. Male and female skulls were identified by assuming males were more robust than females, though both were unusually strong compared to other Asian H. erectus. Adult skulls averaged 202 mm × 152 mm (8.0 in × 6.0 in) in length and width, similar in shape to Peking Man but with a larger circumference. Skull V was 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 earlier Javan H. erectus, including larger brain size, a higher cranial vault, less postorbital narrowing, and less developed brow ridges. They still closely resemble earlier H. erectus. Like Peking Man, a slight ridge ran across the middle of the skull. Compared to other Asian H. erectus, the forehead was proportionally low and sloped at a shallow angle. The brow ridges curved downward in the center, forming a nasal bridge, and were especially thick at the sides. Like Peking Man, the frontal sinuses were limited to the area between the eyes. The area where the temporal muscle would attach was flat, unlike in Neanderthals and modern humans. The brow ridges connected to thick cheekbones. The skull was narrow compared to the cheekbones, making the cheekbones visible from above. The triangular shape of the temporal bone and the sharp infratemporal crest matched Peking Man. The inferior and superior temporal lines on the parietal bone spread apart toward the back of the skull, similar to earlier Javan H. erectus.
At the back of the skull, a sharp, thick bar of bone (called the occipital torus) separated the occipital and nuchal planes. This bar was most prominent where the external occipital protuberance is in modern humans. The base of the temporal bone matched Java Man and Peking Man rather than Neanderthals or modern humans. A bony pyramid near the pterygoid bone was present, unlike in Neanderthals and modern humans. The mastoid part of the temporal bone jutted out. The occipital condyles (which connect the skull to the spine) were smaller compared to the foramen magnum (where the spinal cord enters the skull). Large, irregular bony projections were found behind the occipital condyles.
Brain volume measurements for six Ngandong specimens ranged from 1,013 to 1,251 cc (61.8 to 76.3 cu in). The Ngawi I skull measured 1,000 cc (61 cu in), and the three Sambungmacan skulls measured 1,035, 917, and 1,006 cc (63.2, 56.0, and 61.4 cu in). This averages over 1,000 cc (61 cu in). Asian H. erectus typically had brain volumes averaging around 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), which overlaps with modern human variation. The base of the braincase and brain were flat rather than curved. The sella turcica (a bone structure near the pituitary gland) was much larger than in modern humans, which some scientists linked to an enlarged gland causing thickened bones.
Of the two known tibiae, Tibia A was more robust than Tibia B and similar to Neanderthal tibiae. Like other H. erectus, the tibiae were thick and heavy. Based on a reconstructed length of 380 mm (15 in), Tibia B may have belonged to a person about 158 cm (5 ft 2 in) tall and 51 kg (112 lb) in weight. Tibia A likely belonged to a taller individual. Asian H. erectus height estimates (based on a small sample) ranged from 150–160 cm (4 ft 11 in – 5 ft 3 in), with Indonesian H. erectus in tropical areas generally taller and continental specimens in colder regions shorter. The single pelvic fragment from Ngandong has not yet been formally described.
Culture
The Ngandong fauna is similar to the older Kedung Brubus fauna, which lived about 800,000 to 700,000 years ago. This was a time when many large mammals, such as Asian elephants and Stegodon, moved to Java. Other animals found at Ngandong include a type of tiger called Panthera tigris soloensis, Malayan tapirs, hippos, sambar deer, water buffalo, a type of cow called Bos palaesondaicus, pigs, and crab-eating macaques. These animals suggest the area had an open woodland environment. The presence of common cranes at the nearby Watualang site might mean the climate was cooler than today. The driest conditions likely occurred about 135,000 years ago, when the Sunda shelf was exposed, connecting major Indonesian islands to the continent. By 125,000 years ago, the climate became wetter, turning Java into an island and allowing tropical rainforests to grow. This change led to the Ngandong fauna being replaced by the Punung fauna, which includes modern-day animals like orangutans and gibbons. These animals likely arrived after Java was reconnected to the continent around 80,000 years ago. H. erectus, which lived in woodlands and savannahs, probably went extinct when these habitats disappeared.
H. e. soloensis was the last group of H. erectus to live in Java. They lived there from about 1.51 to 0.93 million years ago at the Sangiran site, then from 540,000 to 430,000 years ago at the Trinil site, and finally from 117,000 to 108,000 years ago at Ngandong. If the dates are correct, they may have been the last H. erectus to survive in the open areas of East Asia before rainforests spread. Before modern humans arrived, Late Pleistocene Southeast Asia also had H. floresiensis on Flores, Indonesia, and H. luzonensis on Luzon, the Philippines. DNA studies of modern Southeast Asian people show that Denisovans, a group known only by their genetic traces, lived widely across Southeast Asia. They had children with early modern humans about 45,700 and 29,800 years ago. A 2021 study found that modern humans did not interbreed with these other human species, unless their offspring could not survive or their families died out.
Many H. e. soloensis bones were found at Ngandong, suggesting a large population lived there before a volcanic eruption buried them. However, it is hard to know the exact population size. Ngandong was far from Java’s northern coast, but the location of the southern shoreline and the mouth of the Solo River is unclear.
In 1936, Oppenoorth studied photos of bones found by Dutch archaeologist Pieter Vincent van Stein Callenfels. He noticed broken bones, including a large tiger skull and deer antlers, and thought they showed evidence of bone tools. He suggested some antlers had carved bird skulls attached to make axes. In 1951, Weidenreich doubted this, saying the bones were likely damaged by the river, crocodiles, or other natural processes. 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 daggers or arrowheads, like tools used by some South Pacific people today. It is unclear if these tools were made by H. e. soloensis or later humans. Earlier H. erectus at Trinil may have used shells and shark teeth to make tools.
Oppenoorth also found a round andesite stone ball at Ngandong, which was common in the Solo Valley. Similar balls were found in European and African sites as old as the Acheulean period in Kenya. These balls were once thought to be hunting tools like bolas, but a 1993 study by American scientists showed they could be made by using them as hammers.
In 1938, von Koenigswald and other archaeologists collected stone tools, such as cores and flakes, from Ngandong. However, river damage made it hard to tell if these were actual tools. The tools were small, simple, and mostly made of chalcedony, chert, or jasper. Some volcanic rocks and wood were modified into heavy tools. A 1973 discovery at Sambungmacan included a unifacial chopper made of andesite. Because so few tools were found, it is hard to classify H. e. soloensis into a specific tool-making group. Unlike sites in Africa and Western Eurasia, Ngandong lacks complex tools like hand axes. In 1948, Movius suggested this was because H. erectus in East Asia lived in rainforests, where big game hunting was less common.
Although the "Movius Line" theory is not widely supported now, hand axes are still rare in East Asia compared to the West. Some scientists think this is because early humans in East Asia had fewer high-quality materials, used bamboo instead of stone, or had smaller populations.
In 1951, Weidenreich and von Koenigswald studied Skulls IV and VI, which had injuries from a cutting tool and a blunt object. These injuries healed, so the individuals likely survived. Only the skullcaps were found, without teeth, which is unusual. They believed these skulls were from people who were attacked but did not die.