II. Read the following text paying attention to the highlighted words. Explain or interpret the contextual meaning of the underlined phrases

Human beings, extant and extinct, comprise the zoological family Hominidae; and the single living human species, Homo sapiens, is one of some 200 species of the order Primates, in turn one of 20 orders constituting the vertebrate class Mammalia. Within the Primates are included such divergent creatures as the Southeast Asian tarsiers, the Madagascan lemurs, the South American monkeys, the African monkeys, the great apes or pongids (gibbons, orangutans, chimpanzees, gorillas), and finally, humans themselves. The brains of larger tailless anthropoid apes, although much smaller than a modern human brain, are relatively well developed as compared with lower primates and have the same patterns of convolutions as the human brain has. Thus, the sensory and motor mechanisms fulfill functions closely reproducing those of the human brain. Many features of the skull and skeleton of the large apes approximate very closely those of the Hominidae, particularly if account is taken of certain extinct primitive hominids. Some of the structural similarities in the skeleton of the trunk and limbs are in part related to posture, for the chimpanzee and gorilla are capable, at times, of balancing themselves on their hind limbs in a manner that suggests, albeit distantly, the erect posture characteristic of the Hominidae. Many of the muscles of the human body have the same disposition and attachments as those of the anthropoid apes. The disposition of the abdominal organs in apes corresponds quite closely with that of man, and even in their microscopic details some of the organs of the body show a remarkable resemblance. These examples of anatomic and physiological similarities between the large anthropoid apes and the Hominidae could well be multiplied. Their implications for a real phylogenetic relationship are further supported by reference to similarities in serum protein patterns, immunologic responses, some of the blood groups, parasitic infestation, and susceptibility to certain diseases.

The main stages of hominid evolution are represented by the australopithecines, Homo habilis, Homo erectus, and Homo sapiens. We shall concentrate on the evolution and adaptations of the only existing species of the genus Homo – Homo sapiens.

Homo sapiens emerged during the Pleistocene epoch, which was marked by the gradual onset of a cooler climate in many parts of the world about 2.5 million years ago and by a general lowering of temperature that finally led to the great Ice Ages. Fossil remains of early Homo sapiens are known from sites in Africa, the Middle East, and Europe, but later examples come from a wide range of sites in the Old World as a whole. The human skull is composed of both cranial and facial portions. The cranium consists of the skull vault and base, while the facial skeleton consists of the region of the eye sockets, nose, cheekbones, upper jaw (orbital and maxillary region), and the region of the lower jaw (mandibular region). During the evolution of the hominid skull from its apelike precursors, there are a number of general trends that can readily be discerned. The principal trends are the gradual increase in brain size (as measured by cranial capacity), the rounding of the cranial vault, and the gradual reduction of the size of the whole masticatory complex, including both the upper and lower jaws and the teeth. These trends lead to an overall change in skull shape and proportions, so that, while the vault expands, the “muzzle” tends to retract from a protruding (prognathic) form to a straighter-faced (orthognathic) appearance. At the same time, the whole skull tends to become lighter and more delicate in its structures. The dental characteristics of H. sapiens revolve around the basic fact of reduction of the masticatory apparatus. Thus, the dentition as a whole shows tooth crowding (dento-alveolar disproportion), accompanied by smallness of the individual teeth and marked reduction in size of the third molar.

The form of the skeleton of the trunk and limbs of Homo sapiens (postcranial skeleton) is characterized by its adaptation for a fully upright posture and a striding bipedal gait. This remarkable locomotor capability is the final expression of an evolutionary process that has taken at least four million years to achieve, and so some aspects of the process are well known from earlier members of the genus Homo and also from the genus Australopithecus.

In terms of posture, the bipedal vertebral column is held upright and shows two secondarily developed curves when viewed from the side, one in the lumbar region of the back (small of the back) and the other in the neck region. From the front the column should appear straight. These curves allow the weight to be evenly disposed about the line of gravity, which passes vertically through the second sacral vertebra (at the base of the spine) and behind the rotation centres of the two hip joints. This permits the pelvis to tip backward just beyond the vertical and rest upon a strap-like ligament across the front of the hip joint, a sophisticated effort-saving mechanism that allows most of the muscles around the hip to relax so that the upright stance is an economical posture. Associated with this is the ability to lock the knees back, which also relaxes some surrounding muscles. To rise from the squatting or seated position requires considerable power of extension of the hip joints, and this is provided by the large buttock muscle (gluteus maximus) and a backward extension (posterior superior iliac spine) of the bony pelvic flange (blade of the ilium) for its attachment.

An alternating bipedal gait, to be fully efficient, must allow each leg to swing clear of the ground during walking; this is provided for by a pelvic-tilt mechanism that raises the side of the swinging leg. In addition, such a gait must avoid wild side-to-side movements of the centre of gravity, and this is achieved by inclining the thighbones toward the midline and thus bringing the feet closer together. Finally the bipedal adaptations of the modern human foot are such that both weight and force are transmitted to the ground through a propulsive system of short levers that permits a heel–toestride.

The upper-limb adaptations to bipedalism are fewer and are concerned with the dynamic balance of the body while moving. Arm swinging is a normal part of bipedalism and compensates for the twist of the body toward the side opposite to the advancing foot. The selective advantages of bipedalism, in terms of the upper limb, are immense in that they free the hands for the carriage of infants, food, tools, or weapons, as well as permitting the development of the hands for a manipulative role such as tool making. Although hominids below the human level of evolutionary advance could make tools, the refinement and exploitation of tools demanded hands capable of both power and precision grips. The power grip involves primarily the inner, or ulnar, side of the hand and permits a firm grip on a branch, a rock, or hammer handle. The precision grip involves the outer, or radial, fingers and thumb, as in using a small stone for engraving, a small brush for painting, or a pen for writing. This requires the bringing together of the tips of the opposed thumb and the next two fingers in order to grip a small object, a grip that demands that the lengths of the index finger and thumb be proportionate and that the joint at the base of the thumb be of a special saddle-shaped variety. It seems likely that the precision grip evolved later than the power grip and that its perfection may even have been a specialization in Homo sapiens. Only when human hands had evolved to this level, concomitantly with brain expansion, could manipulative skills give expression to the artistic impulse in terms of cave painting, bas-relief, and sculpture in the round, all of which are sophisticated behavioral correlates of a highly evolved individual, in terms of both locomotor and intellectual skills.

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VII. Using additional sources of information prepare a report on one of the following topics and present it to the class	\|	Vocabulary notes

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