12th Class Biology Origin of Life Human Evolution

Human Evolution

Category : 12th Class

During the course of evolution different animal species evolved special organs for a successful life like wings in insects, birds and bats for flying, claws for holding, burrowing and climbing in rats and squirrels and fins or paddles in aquatic life for swimming. Similarly, most significant event in human evolution has been evolution of brain which enabled him to become most superior member of animal kingdom. The large and more complex brain evolved greater ability of thinking, logical power and capacity of taking decisions depending on the situation.

Present human species is named as Homo sapiens sapiens (Sapient = wise). T. H. Huxley (1863) in his book ‘Man's Place in Nature’ made first attempt to explain scientific grounds of upbringing of man. Charles Darwin (1871) in his book ‘The Descent of Man’ gave his ideas about ancestry of man.

(i) Systematic position of man in animal kingdom  

Phylum                            :       Chordata

Subphylum                    :       Vertebrata

Class                                 :       Mammalia

Order                               :       Primates                                   

Suborder                        :       Anthropoidea

Superfamily                  :       Hominoidea

Family                             :       Hominidae

Genus                              :       Homo

Species                            :       sapiens

(ii) Place of descent of man : Available fossils give the evidence that most of the fossils of prehuman ancestors including monkeys and apes have been recovered from Africa, Asia and Europe. However, descent of man is supposed to have occurred in Asia due to following reasons – (i) Civilization of Asia is oldest. (ii) Asia is the land of origin of all domesticated animals and crop plants. (iii) Migration of many animal species has taken place in Asia. (iv) Fossils of many ancestors of man have been found in Java and China which are part of Asia. (v) Climate of Asia was favourable at that time for the evolution of man.

(iii) Time of descent of man : Although time of descent of man is a controversial subject but fossil evidence indicates that time of evolution of man is from Miocene epoch to the beginning of Pliocene epoch of Tertiary period in Coenozoic era. It can be estimated that ancestral man evolved from man like apes about 1 crore 32 lakh years ago.

(iv) Evolutionary characteristics of man : The modern man possesses following special features, which have been acquired during the course of evolution–

(a) Bipedal locomotion.                                      

(b) Large brain and cranial cavity.

(c) Grasping hands and feet.                                               

(d) Erect posture.

(e) Stereoscopic (binocular) vision.   

(f) Sensitivity

(g) Social organisation.                                                        

(h) Expression by speech.

Morphological changes that have occurred in man during the process of evolution are

(a) Increase in brain size and intelligence.         

(b) Attainment of erect posture.

(c) Flattening of face.                            

(d) Shortening of body hair and reduction in their number.

(e) Elevation and narrowing of nose.

(f) Increase in height.

(g) Reduction of brow ridges.                             

(h) Rounding and enlargement of cranium.

(i) The bowl like form of pelvic girdle and broad ilia to support the viscera.

(j) Formation of chin.

The vertebrates of class mammalia as well as other primates have common ancestory with monkeys and apes. Mammals evolved from primitive reptiles in early Jurassic period (about 210 million years ago).

Humans belong to family hominidae in which Homo sapiens is the only living species. The evolutionary history of man has been built up on the basis of study of fossils and molecular homology.

The earliest hominid stock included fossils of Ramapithecus and Sivapithecus unearthed from Africa and Asia. Several species belonging to genus Homo can be recognised from fossil record. Human evolution took place in Africa and Asia.

A common ancestory for great apes and man has been deduced on the basis of similarities in DNA content, chromosome number and banding pattern of chromosomes.

(v) Early human ancestors : The fossils Ramapithecus and Sivapithecus which lived in Africa and Asia (about 1015 million years ago) are believed to be the forerunners of Hominids. These were first man–like primates. The first fossil of Ramapithecus was a fragment of upper jaw recovered from the Shivalik Hills of India. Ramapithecus and Sivapithecus must have a sort face, small brain case, thickly enameled large teeth and they must have been used to walk on their knuckles.

(a) Australopithecus (the first man–ape) : Its fossils were described by Raymond Adart in 1925 from South Africa. These were intermediate between Ramapithecines and genus Homo.

Australopithecines are considered to be ancestral to all hominids of genus Homo.

Australopithecines must have been small statured averaging about four feet. They walked nearly or completely straight. The vertebral column had a distinct lumbar curve with pelvis broad and basin–like. The teeth were larger than those of modern  man. though jaws and teeth were larger than those of modern man. Their face was prognathous and a chin was absent. The bulge of occipital region was small. Eyebrow ridges projected over the eyes.

Their brain capacity ranged from 450–600 ml i.e., slightly larger than that of modern adult Chimpanzee. Thus, Australopithecine’s  represented man with an ape–brain.

  • Ramapithacus has been known from shivalik hills in India.
  • Australopithecus stood erect.
  • G. E. Lewis discovered fossils of Ramapithacus.
  • Australopithacus have 500 c.c. cranial capacity.

(b) Homo erectus (The forerunner of Modern Humans) : In the Middle Pleistocene period, Australopithecines were succeeded by large brained form which were described under the name Pithecanthropus or Java man. Its first fossils were obtained by Dubois (1891). These were named Pithecanthropus erectus (erect ape–man). Similar fossils were found in a cave near Peking, China, and were named Sinanthropus pekinenis.

Mayer (1950) has replaced these names by Homo erectus–

(1) Java Man (Homo erectus erectus = Pithecanthropus erectus) : Its fossils occurred in the Pleistocene deposits about 500,000 years ago. Its cranial cavity was about 940 c.c; (intermediate between that of Australopithecus (600–700 c.c.) and modern  man (1400–1600 c.c.) It was more than five feet tall with skeleton much like ours. Its forehead was low and slanting. The face was prognathous, and jaws were massive with huge teeth. The chin was absent and bony eye. He might have learnt the use and construction of tools and knew how to lit fire.

  • Fire was first used for protection and cooking by Java man.

(2) Peking man (Homo erectus pekinensis = Pithecanthropus pekinensis–Sinanthropus pekinensis) : These perhaps lived 500,000–2,00,000 years ago. It was very similar to Java man with heavy bony eyebrow ridges, low slanting forehead and chinless face. However, their cranial cavity was much larger as compared to Java man ranging from 850–1200 ml. and averaging 1075 c.c.

  • The skill of pithecanthropus was found in Java.
  • The fossils of sinanthropus pekinensis have been discovered in pleistocene epoch.

(3) Homo sapiens (Late Pleistocene Man) : ­Homo erectus were succeeded by early Homo sapiens, which were described under different names Homo neanderthalensis, Homo heildelbergensis, etc. But, since they are grouped under Homo sapiens.

The fossils of primitive man were found in Europe, Asia and Africa. These are Heildelberg man, Neanderthal man, Solo man and Rhodesian man.

Heidelberg man : Their jaw is large and heavy and lacks a chin. Teeth are like those of modern man. Heidelberg is regarded as an ancestor to Neanderthal man and contemporary to Homo erectus.

Neanderthal man : Their fossils were found in the Neanderthal valley in Germany. Previously, it was named as H. sapiens neanderthalensis. These arose some 1,50,000 years ago and flourished in Europe, Asia and North Africa. These were similar to us below the neck, and were heavily built with outwardly curved thigh bones.

The skull bones were thick, forehead was low and slanting and the eyebrow ridges were heavy. The jaw was deep with no chin. The cranial capacity was about 1450 c.c. (almost equal to the modern man). But its lower and posterior portions were larger than the upper and anterior parts. It was quite intelligent to use and construct tools. It buried its dead and could perform ceremonies as well as constructed hut–like dwelling structures.

  • Neanderthal man lives in cave.

Solo man (Homo solonensis) : Fossils were discovered from the banks of solo river. They had heavy eyebrow ridges but forehead was receding type. Brain capacity was 1300 cc.

Rhodesian man (Homo Rhodesiensis) : Fossils of Rhodensian men were found in Rhodesia in the large limestone cave. Their skull had a cranial cavity about 1300 c.c. with receding forehead and ridge was protruded out.

 

  

Homo sapiens fossils

Cro–Magnon Man : These lived during last 30,000 years or more in Europe. These succeeded Neanderthals and became extinct about 10,000 years ago in the last glacial period.

These were about 180 cm. in height with a large skull, broad face, rounded forehead, narrow nose and a prominent chin. They lacked eyebrow ridges. The cranial cavity was about 1660 c.c. These were cave dwelling and hunters. They made tools from stones and ornaments from ivory.

  • Cro–Magnon had perfectly orthognathus face.
  • Cro–Magnon is the most recent ancestor of “Homo sapiens”.
  • Cro–Magnon man was expert in making tools, weapons, paintings etc.
  • Cranial capacity of modern man is 1350–5000 cm3.

Modern Man (Homo sapiens–sapiens) : After last glacial period i,e., about 10,000 years ago, Homo sapiens–sapiens appeared and began to spread all over the globe. He learned to cultivate plants and domesticate animals of economic importance. These were the first settlers who started living a settled life. 



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