The Human reference article from the English Wikipedia on 24-Apr-2004
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Human

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Humans
Status Secure
Image:Human.png
Image of a man and woman, taken from
the Pioneer 11 spacecraft image.
(Public domain image)
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Subphylum:Vertebrata
Class:Mammalia
Order:Primates
Family:Hominidae
Genus:Homo
Species:sapiens
Binomial name
Homo sapiens
Linnaeus, 1758

Biologists classify humans as a species (Homo sapiens) of primates and the only surviving species of the genus Homo. The species is commonly referred to as "mankind" or "humanity" and its members as "humans", "human beings" or "people". The species name Homo sapiens is an uncountable noun and has no plural form. Man is a male human being and woman is a female human being. Historically, man may refer to all of humanity. There is only one extant subspecies, H. sapiens sapiens; that is, all humans alive today belong to this one subspecies.

Table of contents
1 Origins
2 Physical characteristics
3 Habitats
4 Homo sapiens compared to other species
5 Human activity
6 Sciences about humans
7 See also
8 External link

Origins

According to mainstream biology, the closest living evolutionary relatives to humans are the two species of chimpanzee Pan troglodytes ("common chimp") and Pan paniscus ("pygmy chimp" or "Bonobo"), and to a lesser degree other hominoids such as orangutans and gorillas. Biologists have compared a sequence of DNA base pairs between humans and chimpanzees, and estimated an overall genetic difference of 5% [1]. It has been estimated that the human lineage diverged from that of chimpanzees about 5 million years ago, and from gorillas about 8 million years ago. However, recent news reports of a hominid skull approximately 7 million years old already showing a divergence from the ape lineage strongly suggests an earlier divergence. Some scientists argue that bonobos, chimpanzees and, possibly, gorillas should be lumped into the genus Homo, but this is currently a minority opinion.

Various religious groups have raised objections and controversy concerning the theory of humanity's evolution from a common ancestor with the other hominoids. See creationism and argument from evolution for opposing points of view.

Physical characteristics

The body of humans is described in the human anatomy group of articles. Humans have a wide range of variability in physical and other characteristics.

The evolution of Homo sapiens is characterized by a number of important trends:

How these trends are related, in what ways they have been adaptive, and what their role is in the evolution of complex social organization and culture, are matters of ongoing debate among physical anthropologists.
A human skeletonEnlarge

A human skeleton

Although body size is highly heritable, it is also significantly influenced by environmental and cultural factors such as diet. The mean height of an American adult female is 162 centimetres and the mean weight is 62 kg. Males are typically heavier: 175 cm and 78 kilograms. Humans vary substantially around these means, and the means themselves have varied depending on locality and historical factors.

Human children, typically weighing 3-4 kilograms and 50-60 centimetres in height, are born after a nine-month gestation period. Helpless at birth, they continue to grow for some years, typically reaching sexual maturity at around 12-15 years of age. Boys continue growing for some time after this, often only reaching their maximum height around the age of 18.

Human life expectancy at birth is approaching 80 years in wealthy nations, with the assistance of science and technology, and it is thought that the maximum human life span is about 120 years.

See also human physical appearance.

Habitats

At any given time, virtually all of the 6.3 billion (2003 est) humans live on Earth, with two or three living on the International Space Station. Life in space has thus far been temporary living, with up to ten humans in space at a given time (seven on the Space Shuttle, three on Mir). This is a direct result of humans' vulnerability to radiation. Prior to 1961, all humans were restricted to the earth; Yuri Gagarin was the first human to travel into space. At various periods between 1969 and 1974, up to two humans spent varying amounts of time on the Moon. As of yet, residencies or human explorations on other planets have not come to be.

Of Earth-bound humans, most (61%) live in the Asian region. The vast majority of the remainder live in the Americas (14%), Africa (13%) and Europe (12%).

A huge minority - around 2.5 billion people - live in urban surroundings. Urbanisation is expected to rise drastically during the 21st century. Problems for humans in cities include various forms of pollution, crime and poverty, especially in inner city and suburban slums.

As well as being one of the most numerous mammals, the human species is also the most diverse in its habitat. There are humans living on all of the continents and in a range of climates.

Historically, human settlements have been located at and enlarged by proximity to natural resources such as water, fertile land for growing crops and grazing livestock and, more temporarily, by populations of prey. In many places, due to the advent of trade on a massive scale, these factors are no longer the driving force behind growth and decline.

Homo sapiens compared to other species

Humans often consider themselves to be the dominant species on Earth, and the most advanced in intelligence and ability to manage their environment. This belief is especially strong in Western culture, and is based in part on the Biblical Creation story in which Adam is explicitly given dominion over the Earth and all of its creatures.

Biologists and scientists in general, though, do not consider "dominant" to be a useful term, because the adaptive value of any trait or complex of traits depends on the niche and is highly mutable. From a scientific standpoint, Homo sapiens certainly is among the most generalized species on Earth. Smaller and simpler animals such as bacteria and insects greatly surpass humans in population size and diversity of species, but few single species occupy as many diverse environments as humans. Many other species, for example, are adapted to specific environments, whereas humans rely on the use of fire (see lifeform) and on tools such as clothing and manufactured shelter, which are themselves often produced and used through complex social interactions.

Various attempts have been made to identify a single behavioral characteristic that distinguishes humans from all other animals, e.g. the ability to make and use tools (building shelter, weaving fabrics for clothing); the ability to alter the environment; language; and the development of complex social relationships and structures. Considered in isolation, however, these differences are not absolute, as ethologists have recorded such behaviors in many species. Apes and even birds, for example, are known to "fish" for insects using blades of grass or twigs, and even to shape the tools for that purpose. For these reasons, the idea that making and using tools is a defining characteristic of humans is often considered outdated, though of course no other animal uses tools to the same degree or with the same flexibility as Homo sapiens. Similarly, other animals often have methods of communication, but the degree to which humans create and use complex grammar and abstract concepts in language has not been seen in any other species.

Chomskian linguistics holds that a distinguishing feature of humans is that they are the only extant species with a language instinct - a genetic predisposition that produces a brain mechanism whose function is to acquire a language by observing those around us. Dolphins may also have this trait as they show dialect.

Some anthropologists think that these readily observable characteristics (tool-making and language) are based on less easily observable mental processes that might be unique among humans: the ability to think symbolically. That is, humans can think abstractly about concepts and ideas. They can question, use logic, understand mathematical concepts, and so on in ways greater than other animals are known to do, although several species have demonstrated some abilities in these areas. In any case, the idea that these abilities distinguish humans from other species is the basis of the name Homo sapiens, sometimes translated as "Man the Thinker". It should be noted, however, that the extinct species of the Homo genus (e.g. Homo neanderthalensis, Homo erectus) were also adept tool makers and there is some evidence that they may have had linguistic skills.

While humans have all these characteristics, from the biological viewpoint the question "What single characteristic distinguishes humans from all other animals?" is an odd one: it is not a question that is usually asked of cats, dolphins, or song sparrows. Finding other species that shape tools or can use sign language may shed light on human evolution, but it doesn't erase the differences or similarities between humans and other species.

Human activity

Sciences about humans

See also

External link