Human
Being
Human, common name given to any individual of the species Homo sapiens
and, by extension, to the entire species. The term is also applied to certain
species that were the evolutionary forerunners of Homo sapiens.
Scientists consider all living people members of a single species. The word
‘Human’ is more commonly attributed to Homo sapiens sapiens i.e. the
modern Man. (Latin homo ‘man’, sapiens ‘knowledge’)
Homo sapiens is identified, for purposes of classification, as an animal
(kingdom Animalia) with a backbone (phylum Chordata) and segmented
spinal cord (subphylum Vertebrata) that suckles its young (class Mammalia);
that gestates its young with the aid of a placenta (subclass Eutheria);
that is equipped with five-digited extremities, a collarbone, and a single pair
of mammary glands on the chest (order Primates); and that has eyes at the front
of the head, stereoscopic vision, and a proportionately large brain (suborder Anthropoidea).
The species belongs to the family Hominidae, the general characteristics
of which are discussed below.
The details of skeletal structure distinguishing Homo sapiens from
the nearest evolutionary primate relatives—the gorilla, chimpanzee, and
orangutan—stem largely from a very early adaptation to a completely erect
posture and a two-footed striding walk (bipedalism). The uniquely S-shaped
spinal column places the centre of gravity of the human body directly over the
area of support provided by the feet, thus giving stability and balance in the
upright position. Other mechanical modifications for bipedalism include a broad
pelvis, a locking knee joint, an elongated heel bone, and a lengthened and
aligned big toe. Although varying degrees of bipedalism are seen in other
anthropoids, all have straight or bowed spines, bent knees, and grasping
(prehensile) feet, and all use the hands to bear part of the body weight when
moving about.
Complete bipedalism in the human freed the hand to become a supremely
sensitive instrument for precise manipulation and grasping. The most important
structural detail in this refinement is the elongated human thumb, which can
rotate freely and is fully opposable to the other fingers. The physiological
requirements for speech were secondarily established by erect posture, which
positions the vocal cords for controlled breathing, and by the skilled use of
the hands. The latter development occurs in association with the enlargement and
specialization of a brain area (Broca's convolution) that is a prerequisite for
refined control of the lips and tongue.
The large (averaging 1400 cc/85.4 cu in) brain of Homo
sapiens is approximately double that of early human toolmakers. This great
increase in size in only 2 million years was achieved by a process called
neoteny, which is the prolongation of retention of immature characteristics. The
juvenile stage of brain and skull development is prolonged so that they grow for
a longer period of time in relation to the time required to reach sexual
maturity. Unlike the early human adult skull, with its sloping forehead and
prominent jaw, the modern human skull—with biologically insignificant
variations—retains into maturity a proportionately large size, in relation to
the rest of the body, a high-rounded dome, straight-planed face, and reduced jaw
size, all closely resembling the characteristics of the skull in the juvenile
chimpanzee. Its enlarged dimensions required adaptations for passage through the
birth canal; consequently, the human female pelvis widens at maturity (with some
sacrifice in swiftness of locomotion), and the human infant is born prematurely.
Chimpanzees are born with 65 percent of their adult brain capacity;
Australopithecine, an erect, tool-using near-human of 3 million years ago, was
born with about 50 percent; modern human newborns have only 25 percent of adult
brain capacity, resulting in an extended period of helplessness. The many
neurological pathways to the rapidly growing brain must be organized and
coordinated during a prolonged period of dependency on and stimulation by
adults; lacking this close external bond in the early years of life, development
of the modern brain remains incomplete.
The physiological adaptations that made humans
more flexible than other primates allowed for the development of a wide range of
abilities and an unparalleled versatility in behaviour. The brain's great size,
complexity, and slow maturation, with neural connections being added through at
least the first 12 years of life, meant that learned behaviour could largely
modify stereotyped, instinctive responses. New environmental demands could be
met by rapid adjustments rather than by slow genetic selection; thus, survival
in a wide range of habitats and under extreme conditions eventually became
possible without further species differentiation. Each new infant, however, with
relatively few innate traits yet with a vast number of potential behaviours,
must be taught to achieve its biological potential as a human. The human species
has a unique capability for culture in the sense of conscious thinking and
planning, transmission of skills and systems of social relationships, and
creative modification of the environment. The integrated patterns of behaviour
required for planning and fashioning tools were accomplished at least 2.5
million years ago, and some form of advanced code for vocal communication may
also have existed at this time. By 350,000 years ago planned hunting, fire
making, and the wearing of clothing were well established, as was possibly
ritualised disposal of the dead. Evidence of religion, recorded events, and art
date from 30,000 to 40,000 years ago and imply advanced language and ethics for
the complex ordering of social groups required for such activities. From about
that time the genus Homo began to stabilize into the one generalized species of Homo
sapiens.