|Description of Homo sapiens: |
Human beings, humans, or Homo sapiens sapiens (Homo sapiens is latin and refers to the wise or knowing human) are bipedal primates in the family Hominidae. DNA evidence indicates that modern humans originated in Africa about 250,000 years ago. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and emotion. This mental capability, combined with an erect body carriage that frees the forelimbs (arms) for manipulating objects, has allowed humans to make far greater use of tools than any other species. Humans currently inhabit every continent on Earth, except Antarctica (although several governments maintain seasonally-staffed research stations there). Humans also now have a continuous presence in low Earth orbit, occupying the International Space Station. The human population on Earth is greater than 6.7 billion, as of July, 2008.
Like most primates, humans are social by nature. However, they are particularly adept at utilizing systems of communication for self-expression, exchanging of ideas, and organization. Humans create complex social structures composed of many cooperating and competing groups, from families to nations. Social interactions between humans have established an extremely wide variety of traditions, rituals, ethics, values, social norms, and laws, which together form the basis of human society. Humans have a marked appreciation for beauty and aesthetics, which, combined with the desire for self-expression, has led to innovations such as culture, art, literature and music.
Humans are notable for their desire to understand and influence the world around them, seeking to explain and manipulate natural phenomena through science, philosophy, mythology and religion. This natural curiosity has led to the development of advanced tools and skills; humans are the only currently known species known to build fires, cook their food, clothe themselves, and manipulate and develop numerous other technologies. Humans pass down their skills and knowledge to the next generations through education.
The scientific study of human evolution encompasses the development of the genus Homo, but usually involves studying other hominids and hominines as well, such as Australopithecus. Modern humans are defined as the Homo sapiens species, of which the only extant subspecies - our own - is known as Homo sapiens sapiens. Homo sapiens idaltu (roughly translated as elder wise human), the other known subspecies, is now extinct. Anatomically modern humans first appear in the fossil record in Africa about 130,000 years ago, although studies of molecular biology give evidence that the approximate time of divergence from the common ancestor of all modern human populations was 200,000 years ago.
The closest living relatives of Homo sapiens are the two chimpanzee species: the Common Chimpanzee and the Bonobo. Full genome sequencing has resulted in the conclusion that after 6.5 [million] years of separate evolution, the differences between chimpanzee and human are just 10 times greater than those between two unrelated people and 10 times less than those between rats and mice. Suggested concurrence between human and chimpanzee DNA sequences range between 95% and 99%. It has been estimated that the human lineage diverged from that of chimpanzees about five million years ago, and from that of gorillas about eight million years ago. However, a hominid skull discovered in Chad in 2001, classified as Sahelanthropus tchadensis, is approximately seven million years old, which may indicate an earlier divergence.
The Recent African Origin (RAO), or the - out-of-Africa-, hypothesis proposes that modern humans evolved in Africa before later migrating outwards to replace hominids in other parts of the world. Evidence from archaeogenetics accumulating since the 1990s has lent strong support to RAO, and has marginalized the competing multiregional hypothesis, which proposed that modern humans evolved, at least in part, from independent hominid populations. Geneticists Lynn Jorde and Henry Harpending of the University of Utah propose that the variation in human DNA is minute compared to that of other species. They also propose that during the Late Pleistocene, the human population was reduced to a small number of breeding pairs, no more than 10,000, and possibly as few as 1,000, resulting in a very small residual gene pool. Various reasons for this hypothetical bottleneck have been postulated, one being the Toba catastrophe theory.
Human evolution is characterized by a number of important morphological, developmental, physiological and behavioural changes, which have taken place since the split between the last common ancestor of humans and chimpanzees. The first major morphological change was the evolution of a bipedal locomotor adaptation from an arboreal or semi-arboreal one, with all its attendant adaptations, such as a valgus knee, low intermembral index (long legs relative to the arms), and reduced upper-body strength.
Later, ancestral humans developed a much larger brain â typically 1,400 cmÂ³ in modern humans, over twice the size of that of a chimpanzee or gorilla. The pattern of human postnatal brain growth differs from that of other apes (heterochrony), and allows for extended periods of social learning and language acquisition in juvenile humans. Physical anthropologists argue that the differences between the structure of human brains and those of other apes are even more significant than their differences in size.
Other significant morphological changes included: the evolution of a power and precision grip; a reduced masticatory system; a reduction of the canine tooth; and the descent of the larynx and hyoid bone, making speech possible. An important physiological change in humans was the evolution of hidden oestrus, or concealed ovulation, which may have coincided with the evolution of important behavioural changes, such as pair bonding. Another significant behavioural change was the development of material culture, with human-made objects becoming increasingly common and diversified over time. The relationship between all these changes is the subject of ongoing debate.
The forces of natural selection continue to operate on human populations, with evidence that certain regions of the genome display directional selection in the past 15,000 years.
This description from WikiPedia, 3rd August 2008: http://en.wikipedia.org/wiki/Homo_sapiens