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According to the theory of evolution, the development of genus Homo spans over 2 million years although the fossil record is far from complete; as paleoanthropologists discover new evidence, models of human evolution change.

Anthropologists generally recognize three species of hominenes:

• Homo habilis,
• Homo erectus
• Homo sapiens

All human beings today belong to the same subspecies, Homo sapiens sapiens.

There is ongoing debate over whether "Neanderthal Man" was a separate species, Homo neanderthalensis, or a subspecies of H. sapiens.

H. habilis, the first species of genus Homo, evolved in South and East Africa in the late Pliocene or early Pleistocene (2 - 2.5 million years before present) when it diverged from the Australopithecines ( Australopithecines and Hominenes are collectively referred to as Hominids). Both genera were bipedal. H. habilis had smaller molars and larger brains than the Australopithecines, and tools made from stone and perhaps animal bones.

In the Early Pleistocene, from 1.5 to 1 million years ago, hominines in Africa, Asia, and Europe, evolved larger brains and made more elaborate stone tools; these differences and others are sufficient for anthropologists to classify them as a new species, Homo erectus.

Human babies have far more fat reserves than other primates. It has been hypothesized that this is necessary to ensure brain development during times of food shortages (the brain consumes 60% of a baby's energy intake).

The conventional view of human evolution states that humans evolved in inland savanna environments. However, these areas would not have consistently provided a steady and varied enough diet to allow for proper brain development for many infants of early non-hunting hominids, says Stephen Cunnane of the University of Toronto. Shore based environments, however, would have been able to provide enough calories, iodine and omega fatty acids essential to brain growth. Such observations have lead, in part, to the aquatic ape theory. Unfortunately, proving this hypothesis will be difficult because of the fact that many near-shore environments available to our early ancestors are now submerged due to a global rise in sea level.

Between 400,000 years ago and the second interglacial period in the Middle Pleistocene, around 250,000 years ago, the trend in cranial expansion and the elaboration of stone tool technologies developed, providing evidence for a transition from H. erectus to H. sapiens. The direct evidence suggests that there was a migration out of Africa of H. erectus, then a further speciation of H. sapiens from H. erectus in Africa and a subsequent migration out of Africa which replaced the dispersed H. erectus. There is little evidence that this speciation occurred elsewhere, even though some fossil evidence for H. erectus has been found in China. However, the current evidence doesn't preclude multiregional speciation, either. This is a hotly debated area in paleoanthropology.

Today's

               Uzbekistan-Turkmenistan-Xinjiang area
               had been a cradel of
               Northern Eurasian and Amerind
               populations. Most ancestors of modern
               Europoids, Semites, Iranians, Berbers,
               Uralics, Siberians, Tibetans,
               Chinese, Korean-Japanese, Mongolians,
               Turks and Amerincs inhabited
               this area which was humid and warm
               until 17,000 Before Present.
               About 40,000 BP, the ancestors of
               Europoids and other Caucasoids
               wandered off towards the west,
               splitting in to Europoid,
               Middle-Eastern and Berber groups. The
               population in Central Asia
               continued to evolve in to Mongolinds. In 17,000 BP, due to the climate
               turning cold and dry, several waves of migration started off towards
               the East, some ending up in the American continents, some ending up in
               Southern China and India, blending with populations of Subcontinental
               and Southeast Asian origins. The Central Asian population continued to
               evolve into classical Mongoloids and Tibetans. Finally These groups
               evacuated the inhospitable Central Asia and branched off into Siberia,
               Tibet, China and Mongolia around 6,000 BP. Around 4,000 BP, the
               Indo-Europeans, a group mostly closely resembling, and including the
               Iranians, re-colonized Central Asian with the help of their advanced
               pastoral culture, equipped with horses and wheels. Two Indo-European
               gruops, the Tocharians and Iranians were for a long time masters of
               the Central Asian steppes, the latter having the supremacy in mobility
               and number. Mongolian groups adopted the pastoral culture of the
               Indo-Europeans around 3,000 BP and became very good at it starting
               2,000 BP. Several waves of Mongolian migration, often coupled with
               swift military conquests, started out West, South and East, leaving
               their legacies in Japan, Korea, China, Yakutia, Central Asia,
               Afghanistan, India, Iran, Russia and Europe.

Important fossils:

• Petralona, Greece, about 300k years old. Contained many features of H. erectus.
• Arago, France, about 300k years old. Oldest skull clearly of H. sapiens origin.

The origins of humanity is a subject of great political and religious controversy in the United States and certain other countries. See: creationism.

See also: Homo neanderthalensis.

Location in the evolutionary tree:

• Kingdom Animalia
• Phylum Chordata
• Class Mammalia
• Order Primates
• Suborder Anthropoidea
• Infraorder Catarrhina
• Superfamily Hominoidea
• Family Hominidae

Note: the superfamily Hominoidea includes two other families, Pongidae, which includes the great apes, and Hylobatidae (gibbons and siamangs). Many taxonomists put Pongidae and Hominidae together as one family; see that article.

In science fiction speculation about the future evolution of humans is often explored. Sometimes evolution to a being of pure spirit is imagined, sometimes continued speciation as humans fill various ecological niches, see adaptive radiation.