The Homorectus

It is widely accepted that population similar to Homo erectus was directly ancestral to the earliest members of living species Homo sapiens. The exact timing and mode of transformation are still controversial.

Homo erectus appears to have evolved in Africa about 1.8 million years ago. Migrations first to Asia and then to Europe. the species became extinct sometimes less than .5 million years ago. This timing places Homo erectus between Homo habilis and the earliest appearance of Homo sapiens. The time of migration out of Africa is unknown. Most scholars agreed migration occur about 1 million years ago but there is continue debate over how much earlier than this had begun.

Recently a Homo erectus lower jaw has been found in Georgia and said to be 1.6 million years ago. A number of important firsts were recorded during the Homo erectus’ existence. The first appearance of hominids outside of Africa. The first appearance of systematic hunting. Tool making and use of fire. First indication of extended childhood. Homo erectus was capable of a more complex life. The brain size was increased over halibis ranging between 850 and 1100 cm cube. Body size also increased. Reaching close to 1.8 meters in male and 1.55 meters in females. The cranium is long and low and somewhat flattened at the front and back. The cranial bone being thicker than in earlier hominids. The face is short but wide and the nasal aperture projected forward, suggesting the first appearance of the typical human external nose with the nostril facing downward. Pronounced brow ridges are present above the orbits. The postcranial skeleton is similar to that of modern man but its robust and was clearly heavily muscled. Homo erectus evidently routinely experienced heavy physical exertion. The main distinguishing features between Homo habilis and erectus included the increased brain size, the present of brow ridges, a shortened face, and the projecting nasal aperture. The structure of the nose allows for the condensation of moisture from exhales air. This would be beneficial in a species that pursued an active subsistence strategy in warm and arid habitats.
In the cervical and thoracic vertebrae, the hole through which the spinal cord runs is significantly smaller than modern man-indicating a smaller demand for nerve signal traffic. The spines on all the vertebrae are longer and do not point as far back as modern human. The thighbone is unusual in that the femoral neck is long while the femoral head, which is part of the ball, and socket joint with the pelvis is large. This combination is something of a mix between modern human and australopithecine anatomy.

Modern human have a short femoral neck attached to a large head, while in australopithecines the neck is long and the head is small. The pelvis indicates that the birth canal was smaller than man, which implies that Homo erectus mother would have needed to continue fetal growth rate after birth. More extensive child care was inevitable due to a second altricial condition that the neonatal brain size will tripe in size compared with doubling in size of the ape. Tooth pattern created shift to modern human life history pattern. In apes, first molar eruption occurs over 3 years of age and 40 years lifespan. Humans are 5.9 years and 66 years.

The Turkana boy: a Homo erectus individual who died about 10 years of age, lived 1.6 million years ago west of Lake Turkana in northern Kenya. It is the most complete early human fossil discovered and includes many skeletal elements of Homo erectus nor previously known.

One hallmark of Homoerectus was a stone tool; the teardrop shaped handaxe. These implements which are usually called Acheulian handaxes appear 1.4 million years old deposits at Olduvai Gorge.

Significant behavioral changes than begun with habilis became further developed with erectus. Indicative of such a change was the reduction of body size dimorphism between the sexes. Sexual dimorphism in earlier hominids was large with male being almost twice as bulky as females. A situation that had several possible behavioral implications. It might imply significant competition between males for access to females. With Homoerectus, this ratio dropped considerably, with male only 20-30% larger than females, perhaps implying a significant reduction in competition between males. The greater complexity of Homoerectus lifeways included a degree of male-male cooperation? Whether they use a spoken language is a matter of speculation.Homo erectus has long been regarded as the direct antecedent to Homo sapiens. Recently, this assumption has been questioned. Specifically, several investigators propose that many large brained fossil hominids from the Middle Pleistocene that traditionally have been assigned to Homo erectus in fact belong to several species of Homo, not just one. Homo erectus as currently defined from Asia would be one species which became extinct in the last half million years. The second would be populations similar to Homo erectus. This new and distinctly controversial-view stems from a cladistic analysis of the large collection of African and Asian fossils that traditionally have been assigned to Homo erectus.

The problem of defining Homo erectus is that it is viewed at present as a grade of human evolution intermediate between the small-brained early Pleistocene hominids and the large brained Homo sapiens. The term grade is used to encompass a population that has reached the same adaptive stage. It does not require that the organisms belong to the same group (species). Peter Andrew stated just because the erectus specimens are all the same size or similar size brains is not evidence that they belong to the same species. When the primitive characters are removed from the list of traditional Homo erectus, only a small number of derived characters remains. Significantly, these characters are found exclusively within Asian fossils leaving African fossils outside the group and they don’t form a link with Homo sapiens. In other words, the Asian Homo erectus population appears to be evolutionarily separated from those hominids of a similar grade in Africa, and eventually became extinct. The African populations would have other species names applied to them such as Homo ergaster and Homo leakeyi. One African species of the Homo erectus grade might have been ancestral first to European archaic sapiens and later to anatomically modern humans.