Exploring the Fascinating Journey of Human Evolution

Mind Blowing - Disclaimer: This article is not intended as a reference and is unrelated to any race issues. The content presented is a reconstruction by experts, compiled and summarized from various sources, and based on scientific research findings.

Scientists have discovered a 7.2 million-year-old skull belonging to one of our oldest ancestors and they hope it'll give us a much better understanding of human evolution. (Picture from: ABC.net.au)

The saga of human evolution remains a compelling subject, provoking both interest and debate. Nonetheless, it fuels scientists' unwavering determination to unravel its enigmatic path.

Archaeological excavations at Ga-Mohana Hill North Rockshelter, where crystals and other early evidence for complex behaviors among early Homo sapiens was discovered. (Picture from: CNN)

Human evolution represents the extended transformational journey through which we trace our roots from apelike ancestors. Scientific findings firmly establish that the physical and behavioral characteristics common to all humans evolved from these apelike forebears over a span of roughly six million years.

7.2 - 6.9 million years ago:

Sahelanthropus tchadensis 

This is the oldest human ancestor ever with brain size 340-360 cc. And the Sahelanthropus tchadensis skull was discovered by Michael Brunet's team in Chad in 2001 and described in Nature in 2002. Some suggest that S. tchadensis existed near the time that hominids and apes separated on their evolutionary paths. It could be that this specimen is a representative of an early hominid, predating A. afarensis aferensis by 3 to 4 million years. 

On the other hand, it might be an ancestor of the gorilla. The characteristics of the cranium are a mosaic of hominid-like (short face, the size and shape of the canines), and ape-like (very large brow ridges and small brain case) features.

 
The first early humans, or hominins, diverged from apes sometime between 6 and 7 million years ago in Africa. Sahelanthropus tchadensis has two defining human anatomical traits; 1) small canine teeth, and 2) walking upright on two legs instead of on four legs.

5.8 - 5.2 million years ago:
Ardipithecus kadabba
Found in Ethiopia in 1992. Bipedal (walked upright), probably similar in body and brain size to a modern chimpanzee, and had canines that resemble those in later hominins but that still project beyond the tooth row. This early human species is only known in the fossil record by a few post-cranial bones and sets of teeth. One bone from the large toe has a broad, robust appearance, suggesting its use in bipedal push-off.

The name is derived from the local Afar language. ‘Ardi’ means ‘ground’ or ‘floor’, and is combined with the Latinised Greek word ‘pithecus’, meaning ‘ape’. The species name kadabba means ‘oldest ancestor’ in the Afar language. Scientists originally considered Ardipithecus kadabba to be a subspecies of the later Ardipithecus ramidus, then renamed as its own distinct species based on dental differences.

4.4 - 4.2 million years ago:
Ardipithecus ramidus
Found in Ethiopia in 1992. When paleobiologist Tim White of the University of California, Berkeley, and colleagues described a new human ancestor named Ardipithecus ramidus—or “Ardi”—they challenged many evolutionary assumptions. This 4.4-million-year-old fossil female was bipedal but lived in woodlands, debunking the widely accepted hypothesis that we evolved upright walking on the grassy savanna. Other features hinted that the last common ancestor of humans and chimpanzees was a quadruped and not a knuckle-walking ape, as was long thought.

Over 100 specimens of Ardipithecus ramidus have been recovered in Ethiopia. Even though it has some ape-like features (as do many other early human species), it also has key human features including smaller diamond-shaped canines and some evidence of upright walking. It may have descended from an earlier species of Ardipithecus that has been found in the same area of Ethiopia, Ardipithecus kadabba.

4.2 - 3.9 million years ago:
Australopithecus anamensis
Found in Kenya in 1965. Has a combination of traits found in both apes and humans. The upper end of the tibia (shin bone) shows an expanded area of bone and the orientation of the ankle joint in human-like, indicative of regular bipedal walking (support of body weight on one leg at the time).

Long forearms and features of the wrist bones suggest these individuals probably climbed trees as well. Jaw remains suggest that this species was the direct ancestor of Australopithecus afarensis, and possibly the direct descendent of a species of Ardipithecus.

3.9 - 2.9 million years ago:
Australopithecus afarensis
One of the longest-lived with brain size 375-500 cc. and best-known early human species—paleoanthropologists have uncovered remains from more than 300 individuals! Found between 3.85 and 2.95 million years ago in Eastern Africa (Ethiopia, Kenya, Tanzania), this species survived for more than 900,000 years, which is over four times as long as our own species has been around. It is best known from the sites of Hadar, Ethiopia (‘Lucy’, AL 288-1 and the 'First Family', AL 333); Dikika, Ethiopia (Dikika ‘child’ skeleton); and Laetoli (fossils of this species plus the oldest documented bipedal footprint trails).

Au. afarensis had both ape and human characteristics: members of this species had apelike face proportions (a flat nose, a strongly projecting lower jaw) and braincase (with a small brain, usually less than 500 cubic centimeters -- about 1/3 the size of a modern human brain), and long, strong arms with curved fingers adapted for climbing trees. They also had small canine teeth like all other early humans, and a body that stood on two legs and regularly walked upright. 

Their adaptations for living both in the trees and on the ground helped them survive for almost a million years as climate and environments changed. This species may be a direct descendant of Au. anamensis and may be ancestral to later species of Paranthropus, Australopithecus, and Homo.

3.5 - 3.2 million years ago:
Kenyanthropus platyops
Discovered in 1999 by J. Erus, a member of Meave Leakey's team, west of Lake Turkana, Kenya. In 2001 Leakey, et al. described the specimen in Nature. Leakey and colleagues viewed the finds as being distinct enough from Australopithecus, particularly in the marked flatness of the face, that it justifies giving them a new genus and species, Kenyanthropus platyops (meaning "flat faced hominid from Kenya").

Providing a second hominid species in the period from 3 to 3.5 MYA, the discovery of this specimen challenges A. afarensis "Lucy" as the direct ancestor of modern human. The classification of this specimen as a separate genus is not uncontroversial, especially given the damaged condition (1,100 face pieces) in which the skull was found. Some authorities emphasize that the skull was so deformed that it is difficult to interpret its position in hominid evolution.

2.7 - 2.4 million years ago:
Australopithecus africanus
Found in South Africa in 1924. Was anatomically similar to Au. afarensis, with a combination of human-like and ape-like features with brain size 428-625 cc. Compared to Au. afarensis, Au. africanus had a rounder cranium housing a larger brain and smaller teeth, but it also had some ape-like features including relatively long arms and a strongly sloping face that juts out from underneath the braincase with a pronounced jaw.

Like Au. afarensis, the pelvis, femur (upper leg), and foot bones of Au. africanus indicate that it walked bipedally, but its shoulder and hand bones indicate they were also adapted for climbing. Many scientists consider either this species or Au. afarensis of East Africa to represent a viable candidate for the ancestor of the genus Homo.

2.6 - 2.4 million years ago:
Australopithecus garhi
Found in Ethiopia in 1999. This species is not well documented; it is defined on the basis of 1 fossil cranium and 4 other skull fragments, although a partial skeleton found nearby, from about the same layer, is usually included as part of the Australopithecus garhi sample. The associated fragmentary skeleton indicates a longer femur (compared to other Australopithecus specimens, like ‘Lucy’) even though long, powerful arms were maintained. This suggests a change toward longer strides during bipedal walking.

Some scientists claim that the large molar teeth show that Australopithecus garhi is related to Paranthropus aethiopicus; however, the combination of features of the face, braincase, and teeth are unlike Paranthropus. The scientists who originally reported the finds think that Au. garhi may represent an ancestor of the genus Homo.

2.6 - 2.2 million years ago:
Paranthropus aethiopicus
Found in Kenya in 1985. Still much of a mystery to paleoanthropologists, as very few remains of this speces have been found. The discovery of the 2.5 million year old ’Black Skull’ in 1985 helped define this species as the earliest known robust australopithecine. 

P. aethiopicus has a strongly protruding face, large megadont teeth, and a powerful jaw, and a well-developed sagittal crest on top of skull indicates huge chewing muscles, with a strong emphasis on the muscles that connected toward the back of the crest and created strong chewing forces on the front teeth. 

Paleolithic tools, from the Stone Age 2.6 million years ago. Shrinking forest area, began life on land than ever before in the tree. Many features of the skull are quite similar to Australopithecus afarensis, and P. aethiopicus may be a descendent of this species. It is most likely the ancestor of the robust australopithecine species found later in Eastern Africa, Paranthropus boisei.

2.5 - 1.9 million years ago:
Homo rudolfensis
Found in Kenya in 1972. There is only one really good fossil of this Homo rudolfensis: KNM-ER 1470, from Koobi Fora in the Lake Turkana basin, Kenya. It has one really critical feature: a braincase size of 775 cubic centimeters (estimated has brain size 526-775 cc), which is considerably above the upper end of H. habilis braincase size. At least one other braincase from the same region also shows such a large cranial capacity.

Originally considered to be H. habilis, the ways in which H. rudolfensis differs is in its larger braincase, longer face, and larger molar and premolar teeth. Due to the last two features, though, some scientists still wonder whether this ‘species’ might better be considered an Australopithecus, although one with a large brain!

Developing brain doubled with the expansion front, the area where humans make logical decisions. Most scientists recognize four species that lived in the Turkana Basin, northern Kenya, sometime between 2.0 and 1.5 million years ago: Homo rudolfensis, Homo habilis, Homo erectus, and Paranthropus boisei.

2.5 - 1.6 million years ago:
Homo habillis
Found in Tanzania in 1962. This species, one of the earliest members of the genus Homo, has a slightly larger braincase and smaller face and teeth than in Australopithecus or older hominin species. But it still retains some ape-like features, including long arms and a moderately-prognathic face.

Its name, which means ‘handy man’, was given in 1964 because this species was thought to represent the first stone-tool maker. Currently, the oldest stone tools are dated slightly older than the oldest evidence of the genus Homo.

1.9 - 1.4 million years ago:
Homo ergaster
Found in Kenya in 1984. The Homo ergaster Skull KNM-WT 15000 "Nariokotome Boy" or "Turkana Boy" was discovered by K. Kimeu in 1984 in Nariokotome, Kenya. It was first described by Brown, Harris, R. Leakey and Walker in Nature in 1985 as H. erectus. The completeness of this skull allowed scientists to get accurate measurements of brain size.

Many other skeletal parts were also recovered, giving anthropologists a great deal of information regarding body size, limb proportions, age of death (probably 12 or 13 years) and whether or not language was possible. The pelvis reveals a greater ability to run than modern humans, and some bones reveal a closer affinity to australopithecines.

1.8 million - 20 thousand years ago:
Homo erectus
Found in Indonesia in 1891, estimated has brain size up to 1100 cc. Early fossil discoveries from Java (beginning in the 1890s) and China (‘Peking Man’, beginning in the 1920s) comprise the classic examples of this species. Generally considered to have been the first species to have expanded beyond Africa, Homo erectus is considered a highly variable species, spread over two continents (it's not certain whether it reached Europe), and possibly the longest lived early human species - about nine times as long as our own species, Homo sapiens, has been around! There is probably the first hominins to leave Africa in 790 thousand years ago. Evidence shows started using fire.

600-400 thousand years ago:
Homo heidelbergensis
Found in Germany in 1907. This early human species had a very large brow ridge, a larger braincase (estimated has up to 1100 cc in brain size) and flatter face than older early human species. It was first early human species to live in colder climates, their short, wide bodies were a likely adaptation to conserving heat. 

It lived at the time of the oldest definite control of fire and use of wooden spears, and it was the first early human species to routinely hunt large animals. This early human also broke new ground; it was the first species to build shelters—creating simple dwellings out of wood and rock. The dead began to be buried and there is a primitive language.

250-230 thousands years ago:
Homo neanderthalensis
Found in Belgium in 1829. Neanderthals (Neander-thal, the ‘th’ pronounced as ‘t’) are our closest extinct human relative. Some defining features of their skulls include the large middle part of the face, angled cheek bones, and a huge nose for humidifying and warming cold, dry air. Their bodies were shorter and stockier than ours, another adaptation to living in cold environments. But their brains were just as large as ours and often larger - proportional to their brawnier bodies.

Neanderthals made and used a diverse set of sophisticated tools, controlled fire, lived in shelters, made and wore clothing, were skilled hunters of large animals and also ate plant foods, and occasionally made symbolic or ornamental objects. There is evidence that Neanderthals deliberately buried their dead and occasionally even marked their graves with offerings, such as flowers. No other primates, and no earlier human species, had ever practiced this sophisticated and symbolic behavior. DNA has been recovered from more than a dozen Neanderthal fossils, all from Europe; the Neanderthal Genome Project is one of the exciting new areas of human origins research.

230 thousand years ago - now:
Homo sapiens
Found in Ethiopia in 2003. The species that you and all other living human beings on this planet belong to is Homo sapiens with a brain the size of 1300-1500 cc. During a time of dramatic climate change 200,000 years ago, Homo sapiens (modern humans) evolved in Africa. Like other early humans that were living at this time, they gathered and hunted food, and evolved behaviors that helped them respond to the challenges of survival in unstable environments.

Like other early humans that were living at this time, they gathered and hunted food, and evolved behaviors that helped them respond to the challenges of survival in unstable environments. Anatomically, modern humans can generally be characterized by the lighter build of their skeletons compared to earlier humans. Modern humans have very large brains, which vary in size from population to population and between males and females, but the average size is approximately 1300 cubic centimeters.

Housing this big brain involved the reorganization of the skull into what is thought of as "modern" -- a thin-walled, high vaulted skull with a flat and near vertical forehead. Modern human faces also show much less (if any) of the heavy brow ridges and prognathism of other early humans. Our jaws are also less heavily developed, with smaller teeth. Artistry, pictorial cave about 32,000 years ago.

The following video offers a visual explanation, enhancing the comprehension of the discussed article's context, focusing on the journey of human evolution as substantiated by scientific research.

Now that we understand the findings from scientific investigations, we can hope for a deeper insight into the journey of human evolution. *** [EKA [10082011] | FROM VARIOUS SOURCES | HUMANORIGINS.SI.EDU | CNN | ABC.NET.AU | KORAN TEMPO 3610] 

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