Human





Biologists classify humans as a species (Homo               Humans
sapiens) of primates and the only surviving
species of the genus Homo. The species is          Scientific classification

commonly referred to as "humankind" or "humanity"  Kingdom:    Animalia
and its members as "humans", "human beings" or
"people". (Also sometimes called "man" or          Phylum:     Chordata
"mankind", but that usage is discouraged these     Subphylum:  Vertebrata
days on the grounds of gender neutrality). The     Class:      Mammalia
species name Homo sapiens is an uncountable noun
and has no plural form. Man is a male human being  Order:      Primates
and woman is a female human being. All current     Family:     Hominidae
humans, from across all areas of the Earth, are    Genus:      Homo
of this species: attempts to divide the human
population into "races" are now often considered   Species:    Sapiens

to be spurious.                                          Binomial name
According to mainstream biology, the closest             Homo sapiens
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 evolution of Homo sapiens is characterized by a number of important
trends:

   * expansion of the brain cavity and brain itself, which is typically
     about 1,400 cm3 in volume, well over twice that of a chimpanzee or
     gorilla. Some physical anthropologists argue that a reorganization of
     the structure of the brain is more important than cranial expansion
     itself.
   * canine reduction.
   * bipedal locomotion
   * descent of the larynx (which makes possible the production of the
     complex sound known as vocal language).

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.

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 kilogram. 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. The average
human lifespan is approaching 80 years in wealthy nations, with the
assistance of science and technology.

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 in
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
tools such as clothing and manufactured shelter, which are themselves often
produced and used through complex social interactions.

The use of tools and the ability to alter their environment (building
shelter, weaving fabrics for clothing, language, and the development of
complex social relationships and structures, etc.) has been cited as a
characteristic which distinguishes humans from other animals. This
difference, however, is 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. No other animal uses tools to the same degree or
with the same flexibility as Homo sapiens. Similarly, other animals often
have simple 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, despite much effort to find it.

Chomskian linguistics holds that a distinguishing feature of humans is that
we 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.

Some anthropologists think that these readily observable characteristics
(toolmaking and language) are based on a less easily observable mental
process 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 that no other animals are known to do, although several species have
demonstrated some ability in this area. Nor have other animals demonstrated
any remotely comparable ability to plan their actions. This belief is why
the species was named Homo sapiens, sometimes translated as "Man the
Thinker". Note, however, that the extinct species of the Homo genus (eg,
Homo neanderthalensis, Homo erectus) were also adept tool users and there is
some evidence that they may have had linguistic skills. Moreover, there are
many other animals alive today which use tools, so the idea that making and
using tools is a defining characteristic of humans is often considered outdated.

While humans have all these characteristics, from the biological viewpoint
"what distinguishes humans from all other animals?" is an odd question:
there's no one thing that makes cats, dolphins, or song sparrows unique.
Finding other species that shape tools or can use sign language may shed
light on human evolution, but it doesn't erase the differences between
humans and related species.