There is still so much about human evolution that is unknown even to today's scientists. Exactly how many different species of early humans existed? How were these species related? Were particular species direct ancestors other later species, or did they simply die out without any divergence? So many questions exist in regard to our lineage that it is not possible to say conclusively what has happened throughout the evolution of humans. Despite this, several pieces to the puzzle of human evolution have been uncovered over time, and every day new discoveries allow us to decipher more of the mystery of our evolutionary history. Let us now look the lineage of humans from approximately 4 million years ago.
HUMAN LINEAGE FROM APPROX. 4 MILLION YEARS AGO
Figure 3.1 A drawing of A. ramidus
Figure 3.2 A reconstructed skeleton of A. ramidus, nicknamed "Ardi"
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Ardipithecus ramidus A. ramidus was the last living member of the Ardipithecus group, with the species living approximately 4.4 million years ago. Although dated to be older than the Australopithecus group, A. ramidus was not discovered until after the Australopithecines were well established as a genus of hominins. The reconstruction of a partial skeleton was named 'Ardi,' and the group was named Ardipithecus in order to distinguish them from Australopithecus. Unlike other hominins, A. ramidus had a grasping hallux, or opposable big toe, similar to those of other hominid species adapted for locomotion in the trees. However, they also had features of the pelvis which suggest some degree of bipedalism. It is most likely that A. ramidus were faculative bipeds. |
TIMELINE~4.4 m.y.a: A. ramidus
- Opposable big toes - Pelvis shows adaptations consistent with both bipedal and tree-climbing activity - Reduced canine teeth - Brain size ~300-350cc |
Figure 3.3 A stylisation of Au. anamensis
Figure 3.2 A reconstructed skeleton of A. ramidus, nicknamed "Ardi"
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Australopithecus anamensis
Au. anamensis is the oldest known Australopithecine, having lived somewhere between 4.2 million to 3.9 million years ago. It's classification as an Australopithecine rather than an Ardipithecine is due to the fact that while in species of the Ardipithecus group some bipedalism was used, this is the first hominin species to be mostly bipedal, with the upper end of the tibia (shin bone) found to have an expanded area of bone, consistent with the distribution of body weight on one leg at a time required for bipedal walking. This species lived in woodlands and forests surrounding lakes. They had thickly built but long and narrow jaws, with heavily enamelled teeth. This suggests that they were most likely plant eaters, relying on both fruits and tough foods such as nuts and tubers. |
~4.2 m.y.a: Au. amanensis
- Mostly bipedal - Long 'U' shaped jaw - Small braincase - Heavily enamelled teeth |
Figure 3.5 A facial reconstruction of Au. Afarensis
Figure 3.6 The skeleton of Lucy
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Australopithecus afarensis
This species lived between 3.85 and 2.95 million years ago. One of the longest lived hominin species, they are also one of the species we know the most about, due to fossils from over 300 individuals from the species being discovered. The first of these fossils was the discovery of the famous 'Lucy' skeleton. (see figure 3.4) Named after The Beatles' song Lucy in the Sky with Diamonds which played throughout the celebrations of her discovery in 1974, Lucy was one of the most significant discoveries for paleoanthropologists. With up to 40% of her skeleton, paleoanthropogists were able to learn about the physical characteristics and mannerisms of Lucy's species. For example, Lucy's pelvis, her femur and other lower leg bones show characteristics distinctive of bipedal walking, yet her arms are long and her fingers curved. This ability to both climb and use bipedal locomotion may have been what allowed this species to survive for such a long period of time during changing climates. |
~3.85 m.y.a: Au. afarensis
- Mostly bipedal - Arched feet - Brain size ~400-550cc - Strongly protruding lower jaw and small canines |
Figure 3.7 Facial reconstruction of Au. africanus
Figure 3.8 Cast of the Taung Child skull
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Australopithecus africanus
This was the first early human species to be discovered in Africa, in the year 1924. This species lived between 3.3 and 2.1 million years ago. Although similar to Au. afarensis, Au. africanus had a rounder cranium and smaller teeth. Despite this rounder cranium, Au. africanus had a similar brain size (~400-500cc) to Au. afarensis. Like afarensis, africanus was mostly bipedal, but also had hands and shoulders adapted for climbing. After the discovery of the Taung Child skull in 1924 (figure 3.8) it took the scientific community over 20 years to accept that it was part of the human family tree! |
~3.3 m.y.a: Au. africanus
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Figure 3.9 A proposed reconstruction of Au. garhi
Figure 3.10 A reconstructed Au. garhi skull
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Australopithecus garhi
Au. garhi is not a very well documented species, being defined on the basis of only one fossil cranium, four other skull fragments and one partial skeleton found nearby. Au. garhi is likely to have existed about 2.5 million years ago, and it very similar to other Australopithecine species except for the presence of a longer femur, indicating a move towards longer strides during bipedal locomotion. The large molar teeth indicate some relationship to the Paranthropus group, however features of the face and braincase are unlike this group. Although only speculations, it has been suggested that Au. garhi may have been the first hominins to use stones to break open bones and eat the marrow. The scientists who originally reported the find are of the belief that Au. garhi may be a direct ancestor to the genus Homo. |
~2.5 m.y.a: Au. garhi
- Mostly bipedal - Large molar teeth - Brain size ~420-500cc The Paranthropus group also lived between 2.7 and 1.2 million years ago, however it is not thought that these robust Australopithecines led to the lineage that the genus Homo arose from |
Figure 3.11 Depiction of H. habilis
Figure 3.12 Stone tools found around the same area as H. habilis fossils
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Homo habilis
Homo habilis are the earliest known species of the Homo genus, having lived between 2.4 and 1.4 million years ago. H. habilis has a larger braincase with a smaller face and smaller teeth than Australopithecines, and was named Homo habilis (handy man) because of its suggested use of stone tools (figure 3.12). Despite being classed as a "man", H. habilis still retained some apelike features such as long arms and a moderately sloped face. Although Homo habilis is a well known species, it is poorly defined, with many debates still existing over whether it should be classed as a single, variable species alongside Homo rudolfensis, or whether it is perhaps better classed as an Australopithecine. |
~2.4 m.y.a: Homo habilis
- Hands developed for precision grip, suggesting the use of stone tools - Smaller, straighter face - Smaller teeth - Brain size 510cc |
Figure 3.13 A depiction of H. rudolfensis
Figure 3.14 A H. rudolfensis skull
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Homo rudolfensis
Homo rudolfensis lived around 1.9 to 1.8 million years ago, meaning it existed alongside H. habilis. Only one really good fossil of H. rudolfensis, a skull with a brain size of 775cc, a size far greater than the upper end of H. habilis. Compared to H. habilis, H. rudolfensis had a larger braincase, longer face, and larger molar and premolar teeth. Like H. habilis, there is still ongoing dispute about the classification of H. rudolfensis. Some scientists still argue that H. rudolfensis and H. habilis are a singular, variant species. Other characteristics of H. rudolfensis, such as its enlarged molars and pre-molars, suggest that this hominin is perhaps better classified as an Australopithecine, although one with a very large brain. |
~1.9m.y.a: H. rudolfensis
- Brain size ~775cc - Larger molars and premolars |
Figure 3.15 Facial reconstruction of H. erectus
Figure 3.16 H. erectus skull
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Homo erectus
Homo erectus are the oldest known hominins to possess similar body proportions to modern day humans. This species lived approximately 1.89 million and 143,000 years ago, meaning it existed for nine times as long as our own species have been around! Compared to hominin species before them, H. erectus had longer legs and shorter arms in comparison to their torso indicating the loss of climbing abilities, but the ability to walk or possibly run long distances. They also had larger brains, approximately 900cc. They were also the first species to spread beyond Africa, expanding into Asia, and possibly Europe. |
~1.89m.y.a: H. erectus
- Longer legs, shorter arms - Loss of tree climbing ability - Brain size ~900cc - Expanded into Asia - Cared for the weak and elderly |
Figure 3.17 Model of facial reconstruction of H. heidelbergensis
Figure 3.18 H. heidelbergensis skull
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Homo heidelbergensis
H. heidelbergensis were around approximately 700,000 to 200,000 years ago - during the same time frame as H. erectus. However, this species of early human lived predominately in Europe and Africa, but may have possibly inhabited parts of Asia as well. These were the first humans to live in colder climates, and this is the likely explanation for their short, wide bodies, which would be better adapted to conserve body heat in the cold. They were the first species to routinely hunt large animals, making use of wooden spears and exercise a controlled use of fire. They were also the first species to construct basic shelters out of wood and rock. |
~700,000m.y.a: H.heidelbergensis
- Resided in Europe and Africa - Shorter and stouter - Wooden spears, controlled us of fire, shelters - Brain size ~1200-1300cc |
Figure 3.19 A facial reconstruction of H. neanderthalensis
Figure 3.20 H. neanderthalensis skull
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H. neanderthalensis
H. neanderthalensis, often shortened to Neanderthals, are our closest extinct human relatives. They lived about 400,000 to 40,000 years ago in Europe and central Asia. They were shorter and stockier than H. sapiens, once again an adaptation to the cold climate. Despite this, their brains were actually just as big, and sometimes larger than ours! In addition, they had prominent brow ridges and long faces, particularly through the mid-section. Recent DNA studies have shown that interbreeding between H. sapiens and Neanderthals occurred, and up to 4% of the human genome today consists of Neanderthal DNA. Neanderthals were skilled hunters, and had a diverse range of sophisticated tools. They were also the first known species to deliberately bury their dead. |
~400,000 y.a: H. neanderthalensis
- Resided in Europe and central Asia - Shorter and stockier than H. sapiens - Pronounced brow - Brain size 1225cc - 1750cc - Buried the dead - Created art - Sophisticated tools |
Figure 3.21 Facial reconstruction of H. florensiensis
Figure 3.22 H. floresiensis remains
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Homo floresiensis
H. floresiensis, or "hobbits", were tiny hominins found on the Island on Flores in Indonesia, between 100,000 and 60,000 years ago (this means they also existed alongside Homo sapiens!). They stood just over a metre tall and had tiny brains, with slumped shoulders and receding foreheads. They also had relatively large feet considering the length of their legs, and large teeth for the size of their skull. The "hobbit" is actually likely to be the result of island dwarfism, an evolutionary process whereby large creatures in prolonged isolation on an island become smaller, due to limited resources and a lack of predators. Note: Although the first H. floresiensis members actually lived 100,000 years later than the first H. sapiens, we have included them here on the timeline as H. sapiens are the only human species still existing to present day. |
~100,000 y.a: H. floresiensis
- Nicknamed "Hobbits" - Just over a metre tall - Physical condition probably due to 'island dwarfism' - Brain size 380-420 cc |
Figure 3.23 A facial reconstruction of an early H. sapien
Figure 3.24 A human skull
Figure 3.25 The development of agriculture occurred ~10,000 y.a
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Homo sapiens
Homo sapiens (modern humans) evolved in Africa as early as 200,000 years ago, and now reside worldwide. Anatomically, modern humans are characterised by lightly built skeletons compared to our probable ancestors. The modern human skull is thin walled and high vaulted, with a large, flat forehead to house the large human brain (approx. 1300cc in size). H. sapiens were the first human species to migrate worldwide, and begin to create life as we know it today. The first instance of H. sapien migration out of Africa coincides with a near extinction event, where the human population was reduced to less than 10,000 individuals. This may have been what prompted migration. Several significant technological advancements and cultural developments have occurred throughout the existence of H. sapiens. Our species was the first to develop sophisticated language, and was thought to be the first species to create art until recently Neanderthal artwork was discovered in Gorham's cave, Gibralta in 2014. A boom in technological and cultural developments occurred approximately 50,000 years ago, which interestingly enough, scientists have attributed to a reduction in testosterone levels, something which is consistent with biological evidence such as the further reduction of the brow ridge and development of rounder heads. |
~200,000 y.a: H. sapiens:
- Modern day humans - Lightly built skeleton - Brain size ~1300 cc - Between 70,000 and 60,000 years ago, a near extinction event reduces H. sapien population to <10,000 - 70,000 y.a, H. sapiens migrate out of Africa into Europe and Asia - 60,000-50,000 y.a. H. sapiens reach Indonesia and Australia - 15,000-12,000 y.a. H. sapiens reach the Americas - 10,000 y.a the development of agriculture changes the lifestyle of H. sapiens forever |