More and more species appear in the course of evolution as a historical development of nature. Variety of organisms, which adapt themselves to changes in environmental conditions, increase as the time goes by. As a result living creatures improve and become more complicated. There are supposed to be several periods in human evolution.
Pleistocene is a geological period of the last glacial epoch which included several glaciations. The beginning of this period is characterized by general fall of temperature, appearance of elephant, buffalo and mule. It is considered that during this period ancient humans appeared. It is proceeded by the epoch of pliocene (5,3-1,8 years ago). Environment of Pliocene doesn’t differ much from nowadays world (continents were located in the same way). In the middle of North Atlantic a new island called Iceland appeared. India was moving to the North — collision with Asia caused appearance of the Himalayas. Exactly in this period Antarctica finally isolated from other continents. Separation from South America caused movement towards cold water currents. As a result Antarctica got covered with thick ice crust. It reflects sun rays what leads to further strengthening of cold spell. Pleistocene is considered to be the longest period in the anthropogenic development. Main feature is climate cooling on the Earth, which caused repeated phenomena of cold spells, especially in the Northern Hemisphere. Researches prove that even in tropical areas average temperature was about 6 degrees. First coolings are supposed to emerge in Pliocene. This was not only increase of mountain glacier, but also appearance of continent cooling in Europe, Northern Asia and America. Huge water masses, borrowed from oceans were spent on this process, though after melting water returned. It naturally caused changes of sea level.
Subtropical vegetation transformed into more stable woods and steppes, the majority of mammals died out. Scientists say that Glacial Period is not over yet, but we live in relatively warm epoch. English naturalist Layel considers Pleistocene period to be the last one. Although it wasn’t a catastrophe, this period was of exceptional importance in evolution, changes of Earth structure. Glaciation was twice as much as modern one. Until recently scientists considered that human evolution was more or less strict: one form followed another one, and each new one was more progressive and similar to modern human than previous one. But nowadays it seems to be more complex. Evolutionary tree appeared to be rather branchy. Time intervals are quite degraded. Sometimes several hominid species of different proximity to modern humans could coexist in one environment (Homo ergaster, Paranthropus). The case when hominid family is represented by one human kind as it is nowadays, was not quite typical. For instance, in comparatively recent times (nearly 50 thousands years ago) there were at least 4 hominid species on the Earth, all of them having huge brains: Homo sapiens, Homo neandertalensis, Homo erectus, Homo floresiensis. Homo habilis is the oldest representative of human race, it is to some extent a transitional form between Australopithecus and Homo. Human line, or Hominidae, appeared nearly 5,5-6,5 mln. years ago. It is characterized on the basis of bipedalism (walking on two feet). It is connected with essential changes in lifestyle. That’s why origin of new family Hominidae means at the same time formation of new adaptive zone. In recent years a diversity of ancient hominid were discovered on the territory of Africa. Though many of them dwelled in forests (not in savannas), all of them are supposed to walk on two feet. It prejudices an old theory which claimed that transition to bipedalism was connected with leaving forests and colonization of savannas. This statement is now under consideration of researchers.
The main problem for researchers became identification of exact primates who started hominid race. Some investigators claimed that humans are close to primitive species. Others presumed humans, chimpanzee and gorillas being in close relations and having common ancestors. Three modern forms appeared due to the separation of these species. Hominids posses many anatomic features which isolate them from other primates. Such features appeared as adaptation to life conditions. Orthogradation is a major sigh of humans. Other primates dwell on trees and are actually four-legged, except for several species. Vertical body position deal with secondary adaptive changes, such as feet modification, body proportions etc. Extremely enlarged human brains comparing to other primates is considered to be another adaptive feature. Nerve cells gradually increased. Brain location also changed to some extent. Some modifications provided brains with increased abilities. Another basic change is teeth structure, such as decrease of their length. It closely connected with nutrition changes.
Paranthropus are related to the group of African Australopithecus. But unlike them Paranthropus are larger in size. They were tall and had rather massive constitution, weighing about 70 kilos. A range of features point out that they were probably eating vegetal food. Paranthropus include P.robustus, P.aethiopicus and P.boisei. Their skulls astonish with big jaws and mastication muscles. The first obtained skull was even called “Nutcracker”, due to its teeth. Paranthropus lifestyle resembled modern gorillas’ life in many respects. Obviously they could also make primitive bone tools, with the help of which they picked open termitaries just as gorillas do. It became known that in the course of time Paranthropus vanished from the face of the world. They are supposed to be killed by predators, while Australopithecus and their forerunners successfully learned to cooperate with each other to avoid such poor fate. There’s already been reliable evidences that human ancestors were really hunted by huge beasts. For instance in the caves of Southern Africa researchers discovered our forerunners’ skulls with holes similar to sabre-toothed tiger’s fangs.
Trying to protect themselves from beasts ancient humans were probably cooperating with each other, sharing information about new tools, location of proper stones and other materials. Such places were sometimes situated at a distance of 30 kilometers. So if it were not cooperation it would be hard for a single person to find such tools on their own. It implies certain exchange of information. Though human language in the true sense of this word didn’t exist yet, ancient ancestors possessed high level of communicative abilities, difficult for other living creatures.
In recent years more and more researches are made in the field concerning origin of humans, periods of their existence and modifications into modern mankind. Although lots of assumptions can be made, there is still no true theory of this kind.
Ishida, H., Tuttle, R. Human Origins and Environmental Backgrounds. Springer, 2006.