Life before Humans
Primates ruled mother earth before humans evolved. They are the group of mammals that contains all the species commonly related to the lemurs, monkeys, and apes, with the latter category including humans. Primates are found all over the world. Non-human primates occur mostly in Central and South America, Africa, and southern Asia.
Evolution of primates
Primates arose 85–55 million years ago first as plesiadapiformes from small terrestrial mammals (Primatomorpha), which adapted to living in the trees of tropical forests. The evolutionary history of the primates can be traced back to 65 million years. One of the oldest known primate-like mammal species, the Plesiadapis, came from North America; another, Archicebus, came from China. Other similar basal primates were widespread in Eurasia and Africa during the tropical conditions of the Paleocene and Eocene.
The early primates flourished in Eurasia and a lineage leading to the African apes and humans, including Dryopithecus, migrated south from Europe or Western Asia into Africa. The surviving tropical population of primates gave rise to all living species, from loris to the great apes, which share common ancestors with Homo sapiens.
The lineage of gibbons diverged from the line of great apes some 12-18 million years ago. Molecular evidence also indicates that orangutans diverged from the other great apes at about 12 million years. The fossil of orangutans may be represented by Sivapithecus from India and Griphopithecus from Turkey, dated to around 10 million years ago.
Divergence of the human clade
Between 8 and 4 million years ago, first the gorillas, and then the chimpanzees split off which later evolved to humans. Species close to the last common ancestor of gorillas, chimpanzees, and humans may be represented by Nakalipithecus fossils found in Kenya and Ouranopithecus found in Greece. Human DNA is approximately 98.4% identical to that of chimpanzees when comparing single nucleotide polymorphisms. Around 4 million years ago the African continent was ruled by the genus Australopithecus, including Australopithecus anamensis, Au. afarensis, Au. sediba, and Au. Africanus. The genus recently went to extinction around 2 million years ago.
Evolution of genus Homo
Homo habilis, which evolved around 2.8 million years ago, is considered as the earliest documented representative of the genus Homo. It is also believed that it is the earliest species for which there is positive evidence of the use of stone tools. The brains of these early hominins were about the same size as that of a chimpanzee. During the next million years, with the arrival of Homo erectus and Homo ergaster, cranial capacity had doubled to 850 cm3. Such an increase in human brain size is equivalent to each generation having 125,000 more neurons than their parents. It is believed that Homo erectus and Homo ergaster were the first to use fire and complex tools. They were also capable of starting fires, speech, hunting and gathering in coordinated groups, caring for injured or sick group members, and possibly art-making They spread throughout Africa, Asia, and Europe between 1.3 to 1.8 million years ago.
Homo Erectus are proposed to be the direct ancestors to several human species, such as H. heidelbergensis, H. antecessor, Neanderthals, Denisovans, and modern humans. Homo erectus is the most long-lived species of Homo, having survived for over a million years. By contrast, Homo sapiens emerged about a quarter-million years ago. The modern humans evolved in Africa possibly from Homo heidelbergensis, Homo rhodesiensis or Homo antecessor. They migrated out of the African continent some 50,000 to 100,000 years ago, gradually replacing local populations of Homo erectus, Denisova hominins, Homo floresiensis, Homo luzonensis and Homo neanderthalensis. This migration and origin theory is usually referred to as the “recent single-origin hypothesis” or “out of Africa” theory. Humans lost body hair around one million years ago and the clothes appeared some 70,000 years before humans started to migrate north from Africa into cooler climates.
The forerunner of anatomically modern humans, the Archaic Homo sapiens evolved in the Middle Paleolithic between 400,000 and 250,000 years ago. The transition to behavioral modernity with the development of symbolic culture, language, and specialized lithic technology happened around 50,000 years ago, according to some anthropologists. Homo sapiens neanderthalensis, lived in Europe and Asia from 400,000 to about 28,000 years ago.
Homo sapiens (“wise man”) is the only extant species of its genus, Homo. While some (extinct) Homo species might have been ancestors of Homo sapiens, many, perhaps most, were likely “cousins”, having speciated away from the ancestral hominin line. There is yet no consensus as to which of these groups should be considered a separate species and which should be a subspecies; this may be due to the dearth of fossils or to the slight differences used to classify species in the genus Homo. Evolution has continued in anatomically modern human populations, which are affected by both natural selection and genetic drift. Some of these are due to specific environmental pressures, while others are related to lifestyle changes since the development of agriculture (10,000 years ago), urban civilization (5,000 years ago), and industrialization (250 years ago). It has been argued that human evolution has accelerated since the development of agriculture 10,000 years ago and civilization (Mesopotamia civilization, Aboriginal Australian, Indus valley civilization) some 5,000 years ago, resulting, it is claimed, in substantial genetic differences between different current human populations.