Early human fossils are the preserved physical remains of our ancient relatives, providing direct evidence of human evolutionary history. These remains, which include bones, teeth, and sometimes footprints, serve as windows into the distant past, allowing scientists to reconstruct the physical appearance and behaviors of our predecessors. The study of these fossils is a scientific field known as paleoanthropology.
Key Hominin Ancestors
The human lineage, or hominins, has a diverse family tree with many branches, revealing a complex evolutionary journey. One group is Australopithecus, which lived in Africa between approximately 4 and 2 million years ago. These hominins were among the first to walk upright on two legs, a characteristic known as bipedalism, which allowed them to use their hands for other tasks. While Australopithecus species like Australopithecus afarensis and Australopithecus africanus were bipedal, they also retained some ape-like features, such as small brains averaging 400-500 cubic centimeters, sloping foreheads, and projecting faces. Their teeth, particularly the larger molars and premolars with thick enamel, suggest a diet that included tough, fibrous plant material.
Following Australopithecus, the genus Homo emerged. Homo habilis, known as “handy man,” lived in East and South Africa from about 2.4 to 1.5 million years ago. This species exhibited an increased cranial capacity, ranging from 500 to 900 cubic centimeters, and comparatively smaller molar and premolar teeth than Australopithecus. They are associated with the Oldowan stone tool industry, using simple tools for butchering.
Homo erectus, or “upright man,” succeeded Homo habilis, living from approximately 1.9 million to 143,000 years ago. This species showed a further increase in brain size, averaging around 900 cubic centimeters, and a body size and proportions more similar to modern humans, indicating a commitment to terrestrial bipedalism. Homo erectus was the first hominin to migrate out of Africa, reaching Asia between 2 million and 1.8 million years ago and Europe somewhat later, between 1.5 million and 1 million years ago. They manufactured more advanced Acheulean tools, including handaxes.
Another group is Homo neanderthalensis, or Neanderthals, who inhabited Eurasia from about 400,000 to 40,000 years ago. Neanderthals were cold-adapted, with shorter, stockier bodies, large middle faces, angled cheekbones, and large noses. Their cranial capacity was similar to or larger than modern humans, ranging from 1,200 to 1,750 cubic centimeters, proportional to their more muscular bodies. They developed complex stone tool technology, controlled fire, lived in shelters, and engaged in symbolic behaviors such as deliberate burial of their dead.
Landmark Fossil Discoveries
“Lucy,” a preserved skeleton of Australopithecus afarensis, was discovered in 1974 in the Afar Rift Valley of Ethiopia. Dated to 3.2 million years ago, Lucy’s skeleton, about 40% complete, provided evidence of bipedalism in an early hominin, demonstrating that upright walking evolved long before the development of larger brains.
Another discovery is “Turkana Boy” (KNM-WT 15000), a complete skeleton of a Homo erectus youth found in 1984 near Lake Turkana in Kenya. This specimen, dating to 1.5 to 1.6 million years ago, is the most complete early human skeleton ever unearthed. Turkana Boy’s anatomy, including his long limbs and barrel-shaped chest, provided information about Homo erectus growth rates, body size, and commitment to terrestrial bipedalism. His cranial capacity was 880 cubic centimeters.
The Laetoli footprints, discovered by Mary Leakey and her team in 1976 in Tanzania, offer direct evidence of early hominin bipedalism. These human-like footprints, preserved in volcanic ash and dated to approximately 3.7 million years ago, are attributed to Australopithecus afarensis. The 27-meter-long trail settled debates by showing that hominins were fully bipedal almost a million years before the earliest known stone tools were made.
Unlocking Ancient Lifestyles
Fossil evidence, combined with archaeological findings, provides insights into the daily lives and behaviors of our ancestors. Scientists determine diet by analyzing tooth size, shape, enamel structure, and microscopic wear patterns. For example, pits on tooth surfaces can indicate a diet of hard foods like nuts and seeds, while scratches suggest softer leaves and fruits. Chemical analysis of fossilized bones and teeth reveals the types of plants consumed and whether meat was part of the diet. Evidence from Dikika, Ethiopia, shows cut marks on animal bones dating back 3.4 million years, indicating that Australopithecus afarensis used stone tools to butcher meat.
Locomotion patterns are inferred from skeletal structure and from trace fossils like footprints. While early hominins like Australopithecus combined bipedalism with some arboreal locomotion, later species such as Homo erectus show adaptations for efficient long-distance terrestrial walking. Advanced models and analyses of bone features aid in reconstructing how early humans moved.
Brain development is studied through endocasts, which are natural casts of the interior of fossil skulls. These endocasts allow scientists to estimate brain volume, known as cranial capacity, and infer aspects of cerebral organization. While early hominins like Australopithecus had smaller brains compared to modern humans, there was an increase in brain size over millions of years, leading to complex cognitive abilities. Studies of dental development in early Homo species suggest a prolonged childhood, which may have contributed to increased brain size and complex social behaviors.
Tool use is identified through the presence of stone tools found alongside fossil remains and cut marks on animal bones. The Oldowan tools, dating back 2.6 million years, were simple stone flakes used for cutting and pounding. The later Acheulean tools, appearing around 1.7 million years ago, were more sophisticated handaxes, indicating advanced cognitive abilities and a shift toward a more terrestrial lifestyle for Homo erectus.