What are the characteristics of being human?

Biology Doubts

HUMAN CHARACTERISTICS OF EVOLUTIONARY SIGNIFICANCE

As already explained, Organic Evolution envisages evolution of every modern species by gradual modifications in the body organization of simpler, ancestral forms. Obviously, human genealogy must be traced to such ancestral forms which displayed the first signs of human characteristics. To understand human genealogy, therefore, it is necessary to first enumerate the important evolutionary characteristics of modern “Man” as follows, and also to know the position of human species in the taxonomic hierarchy.

(1) INTELLIGENCE

The modern “Man” excels all other animals in intelligence. Only “Man” is capable of abstract thinking and planning, logical and syllabic speech, and physical expression of emotions by means of facial muscles.

Since the seat of intelligence in animal body is the cerebrum of brain, it follows that, in comparison to all other animals, the “Man” has proportionately the largest brain with most complex cerebrum, especially the neopallium of the cerebrum having numerous sulci (foldings of grey matter). With increasing brain size in human evolution, the volume of cranial cavity and size of skull also increased to accommodate the brain. Consequently, the head became more clearly marked off from the trunk. The cranial capacity of modern “Man” is about 1450 to 1500 (average 1475) cubic centimetres.

(2) ERECT POSTURE AND FREE HANDS

Modern “Man” is the only bipedal animal in strict sense, moving upright and erect on two legs (hind limbs), and using the hands (forelimbs) for purposes other than locomotion. “Man” achieved bipedalism through a series of important evolutionary changes in the body anatomy as follows:

(i) The main body or trunk shortened, while the limbs elongated. The fingers and toes attained flat nails in place of claws.

(ii) The legs elongated relatively more to support the body weight. Their soles flattened, tocs shortened and the hallux became non-opposable. All these features are adaptations for a plantigrade locomotion.

(iii) To accommodate the viscera in a shorter trunk, the thoracic part flattened into a broad chest by flattening of sternum. The pelvic girdle also broadened and became basin-shaped for the same purpose.

(iv) To support the erect trunk, and the upright head on top of it, the vertebral column became shorter, stouter and ‘S-shaped’ by flexing at two places. The lumbar vertebrae reduced in number to 4 or 5 from 6 or 7, and these too started fusing into a single piece, like sacral and tail vertebrae.

(v) The skull shifted to an apical position on top of the vertebral column and became upright due to a forwards and downwards shifting of foramen magnum.

(vi) The face gradually became erect ( orthognathous, instead of prognathous) due to a reduction in length of jaw bones. Moreover, it acquired a forehead to make more space for the brain. It also acquired a chin. Development of orbital or brow ridges above the eyes is also an evolutionary characteristic of “Man”, but these first became more prominent in monkeys and apes, and then reduced during the evolution of human species.

(vii) In accordance with reduced jaws, the teeth lines became semicircular instead of U-shaped. The number of teeth also reduced to 32 from 36. The canines became almost equal to other teeth. The diastema was lost. The dental formula became 2, 1,2,3 from an ancestral formula of 2, 1, 3, 3. The molars acquired five cusps (quinquetubercular) instead of original three. Such a dentition gradually evolved for an omnivorous (generalized) diet from an original insectivorous diet through a herbivorous diet.

(viii) Tail has been lost.

(3) GRASPING

Food is the first basic need of every organism. Hence, when hands became free from locomotion, these were first employed for obtaining food from the environment. For this, the hands became adapted for grasping things. These elongated and became very mobile. The rounded hinge articulation of the head of radius with humerus at the elbow, as well as a gliding carpal joint, were acquired by the hands for a free pronation-supination movement from the originally fixed pronate condition. The fingers also became longer more mobile and grasping developed flat nails and acquired tactile sensitivity at their tips The thumb or pollex became opposable i e at right angles to remaining fingers a condition which is very necessary for grasping

(4) SENSITIVITY

Simultaneously with the evolution of bipedal gait upon open land, the sense of vision became highly developed. The eyes gradually became larger and shifted to a frontal position to attain a 3-dimensional binocular( stereoscopic) vision. Both rods and cones developed in the eyes. The neck also became more mobile to rotate the head for vision in different directions.

Ears became well-developed, but ear pinnae became smaller to facilitate erect posture. The sense of smell ( = olfaction), however, decreased. That is why, the nose of modern “Man” is relatively smaller and narrower with downwardly directed nostrils ( “drop nose”).

(5) REDUCED FERTILITY

Decreased reproduction rate is an evolutionary characteristic of “Man”. The major physical changes in this connection have been formation of scrotal sacs and presence of a prepuce to delay puberty in males, and single uterus, single pair of nipples arid presence of hymen in vagina to delay puberty in females. Moreover, the periods of pregnancy and childhood have increased, and the litter has reduced to normally a single child at a time.

Monogamy, i.e., living of male and female individuals together as a couple, continuous gametogenesis in gonads throughout the year(not seasonal breeding), and a menstruous cycle in females have been the other evolutionary characteristics concerning reproduction.

(6) SPECIAL FEATURES

Rolled out lips, a shallow vertical groove upon upper lip between nose and the mouth, and elevated breasts in females are human evolutionary characteristics of obscure significance.

(7) CULTURE

Increasing intelligence during human genealogy has been the basis of evolution o’ culture, which is an exclusive feature of “M an”. By using its intelligence, “Man” made use of tools and fire, and developed, first a group life and gossip, and then a- well- organized society, art, religion, culture, agriculture, animal husbandry, horticulture language, and- reading and writing.

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What are the characteristics of being human? Pdf

What are the characteristics of being human?

What are the characteristics of being human?

What are the characteristics of being human?

What are the characteristics of being human?

What are the characteristics of being human?

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