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- What Was the First Human Species? - August 26, 2025
The Quest Begins at Seven Million Years
Sahelanthropus tchadensis, commonly known as Toumai, represents what scientists currently consider one of the oldest known hominins, dating back approximately seven million years to the Late Miocene epoch. The first fossils were discovered in northern Chad in 2001 by a research team led by French paleontologist Michael Brunet, including the famous type specimen nicknamed “Toumai.” The name Toumaï comes from the local Dazaga language, meaning “hope of life,” and represents a remarkable window into humanity’s earliest origins. This discovery challenged everything scientists thought they knew about where early humans first appeared, as most previous finds had been concentrated in East and South Africa.
A Skull That Rewrote History
The most significant discovery was a nearly complete, though distorted, cranium that provided crucial evidence about this species’ anatomy and potential behaviors, along with existing fossils that include jaw pieces and teeth making up a head with a mixture of derived and primitive features. The skull housed a brain with a volume of about 360 to 378 cubic centimeters, comparable to that of a modern chimpanzee. Ape-like features included a small brain, sloping face, very prominent browridges, and elongated skull, while human-like features included small canine teeth, a short middle part of the face, and a spinal cord opening underneath the skull. What made this fossil particularly intriguing was its unique combination of characteristics that seemed to bridge the gap between apes and early humans.
The Great Bipedalism Debate
Scientists can determine if extinct hominins were bipedal by examining the position of the foramen magnum at the bottom of the braincase, and in the Toumaï skull, this opening seems positioned fairly forward, which was interpreted as indicating bipedal locomotion. However, this conclusion sparked intense scientific debate. A 2024 study re-examined postcranial evidence and concluded that it is not sufficient to determine whether Sahelanthropus was a habitual biped, since none of the features are consistent with or unique to bipedal hominins. Recently described fossils include a femur found in 2001 near Toumaï and two ulnae, with researchers arguing that the femur has features consistent with bipedalism while the arm bones were clearly adapted to climbing trees.
Orrorin tugenensis: The Original Man
Living around six million years ago, Orrorin tugenensis is one of the oldest early humans on our family tree, with individuals approximately the size of a chimpanzee. French paleontologist Brigitte Senut and French geologist Martin Pickford discovered this species in the Tugen Hills region of central Kenya, finding more than a dozen early human fossils dating between about 6.2 million and 6.0 million years old, giving it the name meaning “original man in the Tugen region.” The most important fossil of this species is an upper femur, showing evidence of bone buildup typical of a biped, indicating that Orrorin tugenensis individuals climbed trees but also probably walked upright with two legs on the ground. This species presents compelling evidence for early bipedalism while maintaining clear arboreal adaptations.
Femur Analysis Reveals Dual Lifestyle
Research discovered that Orrorin’s femur is surprisingly intermediate in both age and anatomy between quadrupedal Miocene apes and bipedal early human ancestors, providing quantitative results of the Orrorin femur as a unique mosaic. The length of the femoral neck in Orrorin tugenensis fossils is elongated and similar in shape and length to modern humans and Australopithecines, appearing to have developed bipedalism six million years ago. Analysis reveals the six-million-year-old “Millennium Man” was bipedal but lived in the trees, providing additional insight into the origins of human bipedalism. This dual adaptation suggests early hominins didn’t abandon their arboreal lifestyle immediately when they began walking upright.
Ardipithecus ramidus: The Ground Floor
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Ardipithecus ramidus was first reported in 1994, and in 2009, scientists announced a partial skeleton nicknamed ‘Ardi’ that provided unprecedented insights into early human evolution. By far the best known early hominin is Ardipithecus ramidus, a 4.4 million year old species from Ethiopia known from a nearly complete skeleton as well as numerous other remains, with a skull that is rather ape-like and broadly similar to Sahelanthropus, featuring a small chimpanzee-sized brain of 300-350cc. White and his colleagues gave their discovery the name Ardipithecus ramidus, where ‘ramid’ means ‘root’ in the Afar language of Ethiopia, referring to the closeness of this species to the roots of humanity. This species lived in forested environments, contradicting theories that bipedalism evolved in response to increasingly open savannas.
Ardi’s Revolutionary Anatomy
The Ardipithecus postcranial skeleton reveals a morphology quite different from living apes, with a shorter, more bowl-like pelvis shape that strongly suggests bipedal walking, but its long forelimbs and fingers and divergent, grasping first toe suggest it spent much of its time in the trees. The foot bones in this skeleton indicate a divergent large toe combined with a rigid foot, and the pelvis, reconstructed from a crushed specimen, shows adaptations that combine tree-climbing and bipedal activity. The overall impression is of a largely arboreal species that walked bipedally whenever it ventured to the ground. This unique combination challenged traditional views of early human evolution and suggested a more complex transition from ape-like ancestors.
The Mystery of Classification
While the hominin status of Sahelanthropus, Orrorin, and Ardipithecus species may be debated, their significance for understanding human origins and evolution is clear, opening a window into the very beginnings of our lineage at the time when our ancestors diverged from chimpanzee cousins. The evidence does not make it easy to work out how these species are related to later hominins or to each other. Some scientists have suggested that we are overestimating the level of species diversity in early hominin fossils and that Ardipithecus, Sahelanthropus, and Orrorin could very likely all belong to the same genus. This ongoing debate reflects the challenges of interpreting fragmentary fossil evidence from such ancient time periods.
Recent Discoveries Challenge Old Models
In May 2023, scientists reported a more complicated pathway of human evolution than previously understood, according to studies showing that humans evolved from different places and times in Africa, instead of from a single location and period of time. These lines of evidence increasingly indicate that H. sapiens originated in Africa, although not necessarily in a single time and place, as it seems diverse groups of human ancestors lived in habitable regions around Africa, evolving physically and culturally in relative isolation until climate changes spurred them to mix and swap genes and tool techniques, eventually giving rise to modern humans. This represents a significant shift from linear evolutionary models toward more complex, interconnected pathways of human development.
The Homo juluensis Discovery
A University of Hawaiʻi researcher says he may have found a new human species called Homo juluensis, which includes mysterious groups like the Denisovans, with Professor Christopher J. Bae studying human ancestors across Asia for more than 30 years and publishing recent research that helps clear up confusion about different types of ancient human-like species that co-existed during the late Middle and early Late Pleistocene, roughly 300,000 to 50,000 years ago. Homo juluensis is defined by a mix of features found in fossils from sites such as Xujiayao and Xuchang in northern and central China, with fossils including large crania with thick skulls, traits reminiscent of Neanderthals, as well as characteristics shared with modern humans and Denisovans. This discovery demonstrates that human evolution continued to be complex and diverse even in relatively recent times.
Environmental Context Matters
Current interpretations suggest that Orrorin is associated with open woodland habitats with dense woodland or forest in the vicinity, while Sahelanthropus is likely found in a mosaic of environments ranging from gallery forest to savanna woodland to open grassland, and Ardipithecus kadabba is associated with riparian woodland and floodplain grassland along water margins. It is considered that six or seven million years ago during the late Miocene, the areas where Sahelanthropus tchadensis inhabited were marshy areas, with evidence from fossil fauna found associated with the remains supporting this hypothesis. These diverse environments suggest that early hominins were remarkably adaptable and not restricted to any single ecological niche.
Genetic Bottlenecks and Population Dynamics
A 2023 genetic study suggests that a human population bottleneck of between 1,000 and 100,000 survivors occurred “around 930,000 and 813,000 years ago and lasted for about 117,000 years and brought human ancestors close to extinction.” Competition between species played a major role in the rise and fall of hominins and produced a ‘bizarre’ evolutionary pattern for the Homo lineage, with research showing for the first time that competition was fundamental to “speciation” across five million years of hominin evolution. This evidence suggests that early human evolution was marked by dramatic population fluctuations and intense competition between different hominin species.
The Tool-Making Revolution
A study from October uses stone tools along with butchery marked bones to expand understanding of earlier hominin diets and ranges, describing sites from Nyayanga, Kenya dating to around three million years ago containing Oldowan stone tools that have traditionally been associated with Homo habilis. At Nyayanga, there are two Paranthropus molars in the same layer as the Oldowan tools and butchered hippo bones but no Homo habilis fossils known from this excavation, suggesting that ruling Paranthropus out as a possible toolmaker is unwise. This discovery pushes back the timeline for stone tool use and suggests multiple hominin species may have been capable of sophisticated tool-making behaviors.
Molecular Clock Insights
Molecular and paleontological evidence now point to the last common ancestor between chimpanzees and modern humans living between five and seven million years ago, with any species considered to be more closely related to humans than chimpanzees being called hominins. The chimpanzee-human divergence date has been estimated to be between 8 and 5 million years ago since the 1960s through immunologic and molecular techniques, driving intensive efforts by different teams to find and explore sediments from this crucial time period, leading to the discovery of several new genera and species of early hominins dated close to the estimated divergence dates. These molecular insights provided the temporal framework that guided paleontologists to search for fossils in the right geological layers.
Current Scientific Consensus
These fossil species between eight million and 4.4 million years old include some of the earliest members of the hominin lineage, with scientists attributing them to five species in three genera: Sahelanthropus, Orrorin, and Ardipithecus, each sharing some traits with better-known human relatives from later in time like Australopithecus, with skeletal adaptations to upright bipedal locomotion being hallmarks of all later hominins found in a limited way in some of these species, suggesting they are more closely related to hominins than the gorilla or chimpanzee lineages. The scientific community continues to debate the exact relationships between these species and their positions on the human family tree.
The question of what was the first human species remains tantalizingly complex. While Sahelanthropus tchadensis currently holds the title as the oldest known potential hominin at seven million years old, the fragmentary nature of early fossil evidence means our understanding continues to evolve. Each new discovery adds another piece to this ancient puzzle, revealing that human evolution was far more intricate and geographically diverse than previously imagined. Rather than a simple linear progression, we’re seeing evidence of multiple hominin species coexisting, competing, and adapting to various environments across Africa and beyond. The story of our origins is still being written with each fossil that emerges from the earth.
