Human evolution is the lengthy process of which people originated from apelike ancestors. Scientific evidence shows that the physical and behavioural traits shared by all people originated from apelike ancestors and evolved over a period of six million years ago.
Man has been a tribal animal since he first walked erect, more than four million years ago. With the impediment of being bipedal, he could not out-climb or outrun his predators. Only through tribal cooperation could he hold his predators at bay.
For two million years, the early hominid was a herd/tribal animal, primarily a herd herbivore. During the next two million years the human was a tribal hunter/warrior. He still is. All of the human’s social drives developed long before he developed intellectually. They are, therefore, instinctive. Such instincts as mother-love, compassion, cooperation, curiosity, inventiveness and competitiveness are ancient and embedded in the human. They were all necessary for the survival of the human and pre-human. Since human social drives are instinctive (not intellectual), they can not be modified through education. As with all other higher order animals, however, a proper behaviour may be obtained through training.
Intellect, the magnitude of which separates the human from all other animals, developed slowly over the entire four million years or more of the human development. Intellect is not unique to the human, it is quite well developed in a number of the other higher animals. Intellect developed as a control over instincts to provide adaptable behaviour. The human evolved to modify/change any behaviour that would normally be instinctive to one that would provide an optimum benefit (survivability). This process is called self-control or self-discipline and is the major difference between the human and the lower order animals, those that apply only instinct to their behavioural decisions. Self-discipline, therefore, is the measuring stick of the human.
The word Hominidae is used to describe the total member species of the human family that have lived since the last common ancestor of both man and the apes. A hominid is an individual species within that family. The field of science which studies the human fossil record is known as paleoanthropology. It is the intersection of the disciplines of palaeontology (the study of ancient life forms) and anthropology (the study of humans). Each hominid name consists of a genus name, which is always capitalized, and a species name, which is always in lower case.
Some controversy exists at the time of this common ancestor to both ape and human, but it is believed to be about 5.5 million years ago. A key fossil record near that time is Ramapithecus, which was believed to be an early hominid for many years, but is now considered an ancient ape that lived near the fork in our common lineage. Ramapithecus is now thought to be an ancestor of the modern apes.
From a genome viewpoint, the difference between modern man and the modern apes is quite small, about 2 percent. From a physical viewpoint, the greatest difference is in locomotion. The human walks upright. It is generally thought that this came about when the ancient hominid adopted the edge of the forest and plain and adapted to a life under the trees as opposed to in them. Fossil evidence shows that this bipedal adaptation was completed quite early, perhaps as early as four million years ago, long before we looked like or thought like we do today. Facial feature changes toward the modern appearance came much later. The facial characteristics of modern man are about 100,000 years old. The faces of earlier hominid were much more apelike.
The earliest fossil hominid, Ardipithecus ramidus, is a recent discovery. It is dated at 4.4 million years ago. The remains are incomplete but enough is available to suggest it was bipedal and about 4 feet tall. Other fossils were found with the ramidus fossil which would suggest that ramidus was a forest dweller.
A new species, Australopithecus anamensis, was named in 1995. It was found in Allia Bay in Kenya. Anamensis lived between 4.2 and 3.9 million years ago. Its body showed advanced bipedal features, but the skull closely resembled the ancient apes.
Australopithecus afarensis lived between 3.9 and 3.0 million years ago. It retained the apelike face with a sloping forehead, a distinct ridge over the eyes, flat nose and a chinless lower jaw. It had a brain capacity of about 450cc*. It was between 3’6″ and 5′ tall. It was fully bipedal and the thickness of its bones showed that it was quite strong. Its build (ratio of weight to height) was about the same as the modern human but its head and face were proportionately much larger. This larger head with powerful jaws is a feature of all species prior to Homo sapiens sapiens.
Australopithecus africanus was quite similar to afarensis and lived between three and two million years ago. It was also bipedal but was slightly larger in body size. Its brain size was also slightly larger, ranging up to 500cc*. The brain was not advanced enough for speech. The molars were a little larger than in afarensis and much larger than the modern human. This hominid was a herbivore and ate tough, hard to chew plants. The shape of the jaw was now like the human.
Australopithecus aethiopicus lived between 2.6 and 2.3 million years ago. This species is probably an ancestor of the robustus and boisei. This hominid ate a rough and hard to chew diet. He had huge molars and jaws and a large sagittal crest. A sagittal crest is a bony ridge on the skull extending from the forehead to the back of the head. Massive chewing muscles were anchored to this crest. See the opening picture of an early Homo habilis for an example. Brain sizes were still about 500cc*, with no indication of speech functions.
Australopithecus robustus lived between two and 1.5 million years ago. It had a body similar to that of africanus, but a larger and more massive skull and teeth. Its huge face was flat and with no forehead. It had large brow ridges and a sagittal crest. Brain size was up to 525cc* with no indication of speech capability.
Australopithecus boisei lived between 2.1 and 1.1 million years ago. It was quite similar to robustus, but with an even more massive face. It had huge molars, the larger measuring 0.9 inches across. The brain size was about the same as robustus. Some scientists believe that robustus and boisei are variants of the same species.
Homo habilis was called the handy man because tools were found with his fossil remains. This species existed between 2.4 and 1.5 million years ago. The brain size in earlier fossil specimens was about 500cc* but rose to 800cc* toward the end of the species life period. The species brain shape shows evidence that some speech had developed. Habilis was about 5′ tall and weighed about 100 pounds.
Homo erectus lived between 1.8 million and 300,000 years ago. It was a successful species for a million and a half years. Early examples had a 900cc* brain size on the average. The brain grew steadily during its reign. Toward the end, its brain was almost the same size as the modern man, at about 1200cc*. The species definitely had speech. Erectus developed tools, weapons and fire and learned to cook his food. He travelled out of Africa into China and Southeast Asia and developed clothing for northern climates. He turned to hunting for his food. Only his head and face differed from modern man. Though proportioned the same, he was sturdier in build and much stronger than the modern human.
Homo sapiens archaic provides the bridge between erectus and Homo sapiens sapiens during the period 200,000 to 500,000 years ago. Many skulls have been found with features intermediate between the two. Brain averaged about 1200cc* and speech was indicated. Skulls are more rounded and with smaller features. Molars and brow ridges are smaller. The skeleton shows a stronger build than modern human but was well proportioned.
Homo sapiens neandertalensis lived in Europe and the Mideast between 150,000 and 35,000 years ago. Neandertals coexisted with H.sapiens (archaic) and early H.sapiens sapiens. It is not known whether he was of the same species and disappeared into the H.sapiens sapiens gene pool or he may have been crowded out of existence (killed off) by the H.sapien sapiens. Recent DNA studies have indicated that the Neandertal was an entirely different species and did not merge into the H. sapiens sapiens gene pool. Brain sizes averaged larger than modern man at about 1450cc* but the head was shaped differently, being longer and lower than modern man. His nose was large and was different from the modern man in structure. He was a massive man at about 5’6″ tall with an extremely heavy skeleton that showed attachments for massive muscles. He was far stronger than modern man. His jaw was massive and he had a receding forehead, like erectus.
Homo sapiens sapiens first appeared about 120,000 years ago. Modern humans have an average brain size of about 1350cc*.
* = cc stands for ‘cubic centimeters’