To begin learning about human evolution and the evidence for it, start with this timeline for the appearance of the important traits that characterize our species.
Human biology and behaviour is the result of more than 5 million years of evolutionary change since our divergence from the chimpanzee lineage. It represents the accumulation of several traits that promoted survival to the variable environments and climates of the African and Eurasian continents.
Bipedalism Appears in the Fossil Record 5-7 Million Years Ago
Walking on two feet is one of the earliest traits that distinguished our own ancestors from the ancestors of modern chimpanzees. Bipedalism may have been beneficial to the earliest humans because it freed their hands for carrying food, offspring, and/or tools, and/or it may have provided a more efficient means of walking long distances. The long arm and finger length of the earliest bipeds indicates that they were still adept at climbing trees, and spent a significant proportion of their time in arboreal settings.
Sahelanthropus tchadensis from sediments in Chad, Africa that are up to 7 million years old (Ma) may be the earliest fossil that displays characteristics of the skull consistent with bipedalism. Genetic evidence situates the chimpanzee-human divergence about 5 Ma. The well-known Ardi specimen (Ardipithecus ramidus) from Ethiopia’s Afar Rift dating to 4.4 Ma was bipedal.
Stone Tool Manufacture Appears in the Fossil Record 2.5 Million Years Ago
Early humans began making stone tools 2.5 Ma. They used hammerstones to detach sharp edged flakes from other stones. These sharp edges were used to cut, scrape, and chop meat, vegetal food, and wood. Stone tools may have allowed early humans to access new resources that they previously did not have access to.
The site of Gona, Ethiopia has yielded the earliest stone tools found thus far. At a nearby site in the Hadar formation, animal bones with stone tool cut marks indicate that stone tools were used to access meat. By 1.8 Ma, stone tools can be found outside the African continent. The way that humans manufactured stone tools has changed significantly since the first appearance of stone tools in the archaeological record.
Homo erectus Exhibits a Larger Brain Size, Longer Childhood and a Human Body Plan 1.9 Million Years Ago
The appearance of Homo erectus about 1.9 Ma signals the origins of three important human traits.Homo erectus exhibits a much larger brain size than earlier human species. Homo erectus children took a relatively long time to grow and thus, relied on parental investment for a longer period of development. This extra time may have allowed for and encouraged cultural behaviors. Unlike earlier humans, Homo erectus has short arms and long legs more adapted for a terrestrial life, suggesting that Homo erecutus did not spend much time in the trees.
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Modern Homo sapiens Appear in the Fossil Record about 190 Thousand Years Ago
The earliest fossils that exhibit all the characteristics of modern humans, including large rounded brain cases and small faces and teeth, date to 190 thousand years ago (ka) at Omo, Ethiopia. Near Herto, Ethiopia, modern human remains are dated to between 154 and 160 ka. Based on mitochondrial DNA sequences, modern African mtDNA has the greatest time depth and suggests that all modern human groups descended from a small population in Africa within the last couple hundred thousand years.
Archaeological Correlates of Symbolic Behaviour Appear 80-100 Thousand Years Ago
The earliest evidence for the production of symbols and the capacity for artistic expression appears in Africa about 80-100 ka. Coastal sites in South Africa have yielded perforated shell beads that may have been used for personal ornamentation (jewellery, clothing decoration), incised lines and geometric forms on the surface of ochre (a red or yellow stone that is sometimes used to make pigments), and new forms of carefully shaped stone points that take a lot of time and effort to shape.
These archaeological finds are suggestive of new technological, symbolic, and economic behaviours unique to modern Homo sapiens. Based on studies of modern African mtDNA lineages the appearance of these behavioural innovations seems to immediately precede a rapid population expansion, migration, and dispersal event 70-60 ka.
The Human Evolution Timeline Can Be Summarized With the Appearances of a Few Key Biological and Behavioural Traits
The evolution of humans was a complicated process that involved dozens of species and at least five different genera. It is important to start with an overview of the key events in the evolution of our species when learning about human origins and evolution. The traits that characterize humans accumulated over the course of at least the last 5 million years. Some of these important traits include bipedalism (5 Ma), stone tool manufacture (2.5 Ma), larger brains, longer childhoods, long legs, and short arms (1.9 Ma), modern human morphology (190 ka), and symbolic behavior (100 ka).
Want to learn about stone tool manufacture and human evolution? Read Human Evolution and Technological Change.
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