Like any other species human also evolved over millions of years. The early stages of human evolution are studied by means of the comparative anatomy of fossils and the evidence of thee comparative biochemistry of present-day humans and other mammalian species. Humans belong to an order of class mammals called Primates. The present day order primates consists of two suborders: Prosimii, includes tree-shrews, lemurs, loris, tarsiers etc. and Anthropoidea, includes monkeys, apes and humans. Humans belong to the family Hominidae. 
In the late 1800s several scientific papers were written on the possible origin of humans. T.H.Huxley (1863) made first attempt to explain the origin of man on scientific basis in his book "Man's place in Nature". Another well known was Charles Darwin's "The Descent of Man"; published in 1871. Darwin suggested that man evolved from ape like ancestors and not the wrong concept that "Man is evolved from monkey". At that time, this concept was strongly criticised by metaphysical and religious circle. At the time of Darwin, no human fossils were known and much less data was available. Since that time, a great number of fossil ape-like creatures were found in Africa and later in Europe and Asia as well. They flourished for many millions of years, and they or their descendents are believed to have evolved into modern apes and humans. Now it is well established that the ansectors of man and ancestors of apes descended from a common ancestor and both human and apes evolved along different lines. The apes of today are highly specialized forms. Human beings are also a highly specialized form.
In the late 1800s several scientific papers were written on the possible origin of humans. T.H.Huxley (1863) made first attempt to explain the origin of man on scientific basis in his book "Man's place in Nature". Another well known was Charles Darwin's "The Descent of Man"; published in 1871. Darwin suggested that man evolved from ape like ancestors and not the wrong concept that "Man is evolved from monkey". At that time, this concept was strongly criticised by metaphysical and religious circle. At the time of Darwin, no human fossils were known and much less data was available. Since that time, a great number of fossil ape-like creatures were found in Africa and later in Europe and Asia as well. They flourished for many millions of years, and they or their descendents are believed to have evolved into modern apes and humans. Now it is well established that the ansectors of man and ancestors of apes descended from a common ancestor and both human and apes evolved along different lines. The apes of today are highly specialized forms. Human beings are also a highly specialized form.
Early Human Ancestors
Primates came into existence about 65 million years ago in Eocene epoch. The first primates were somewhat arboreal forms like present day tree-shrews. They have grasping hands and feet, flat snouts with short noses. These are insectivores. They have large eyes facing more in front than lateral sides. The long bushy tails help them to balance the body while leaping from branch to branch. They show progress in using vision more than the smell.
The prosimians diverged much earlier from the main stock about 60 million years ago during Eocene epoch.
The new world monkeys branched from the ancient primate line about 50 million years ago. After the separation of new world monkeys, the lineage is called anthropoid line. The anthropoids are the acestors of old world monkeys, apes and humans. Their fossils were discovered from Oligocene rocks about 36 to 40 million years old.
The old world monkeys probably diverged from that of antheropoids about 25-30 million years ago in the oligocene epoch.
The lineage remaining after the separation of the old world monkeys is called the hominoid line.
The hominids (Dryopithecus or Proconsul) are the ancestors of apes and humans have been discovered from the rocks of Miocene epoch (about 20-25 million yeats old) in Africa and Asia. The new world monkeys are native to South America. They are flat-nosed monkeys with widely with widely separated and owtwardly directed nostrils. Hence they are named as platyrrhine (Flat Nose). They possess long prehensile tails. They mostly lack the opposable thumb. Their teeth consists of 3 premolars and 3 molars in each half of a jaw. Example: marmosets and spider monkeys. The old world monkeys have a narrow nose with closely placed and downwardly directed nostrils. They are named as Catarrhines (narrow nose). The tails are usually short and never used for swinging from branches. Their thumbs are opposable, and they have only two premolars. These monkeys show better developed and specialized brain, smaller ear pinnae and are capable of expressing their emotions by facial gestures. Examples: baboons and proboscis monkeys.
The subsequent separation of apes and human ancestors occured between 5 and 10 million years ago in the middle of the Miocene epoch.
The apes evolved on two families namely:
a) Family Hylobatidae: includes small sized arboreal Gibbons restricted to Asia only.
b) Family Pongidae: includes Orangutan, Gorilla and Chimpanzee.
The humans evolved on one family namely Hominidae. The apes mainly remained on trees and walked on all four limbs while the ancestors of man came down to ground and walked on two feet. The main changes in the evolution of humans were as follows:
1) The development of an upright posture and bipedal locomotion.
2) Increase in the size of body.
3) Reduction in the size of canine and incisor teeth and in the size of eyebrow ridges.
4) Gradual increase in brain size for higher intelligency and coordination.
5) Development of binocular (steroscpic) vision due to shifting of eyes on front side.
6) Development of grasping power in hands, i.e. thumb opposable to fingers.
7) Arms shorter than legs.
8) Chin distinct, snout absent.
9) Reduction in size of canines.
10) Flattening of face.
Gibbons diverged from the main line about 10 million years ago.
Orangutans diverged about 8 million years ago.
Ancestors of gorilla and chimpanzee separatrd about 4 million years ago.
Gorilla and chimpanzee separated about 2.3 million years ago.
The earliest known direct ancestor of man is genus Ramapithecus that existed about 14 million years ago in Miocene epoch. Its fossils have been found in Africa, Europe and Asia. The first fossil record of Ramapithecus was found in northern Siwalik hills of India. Similarly, a fragment of Jaw of Ramapithecus was recorded in Kenya in 1960 which was about 14 million years old. Munthe et al. (1980) found one of the most important fossils yet collected in Nepal was a hominoid tooth on the bank "New fossil descoveries from the Miocene of Nepal" include a hominoid in 1983. The hominoid specimen was a well preserved left upper first molar 10 mm long and 10.9 mm wide. The tooth was 9 to 9.5 million years old. It's age was determined by palaeomagnetic studies conducted by the university of Wisconsin-Milwaukee, USA. Now it is preserved in the Natural History Museum, Swayambhu, Kathmandu.
a) They were partially uprught and ground-dwelling in Savannah.
b) They were arboreal having man-like feeding habits.
c) They resembled man in having erect posture and small canines.
d) Jaw fragments suggest that they chewed from side to side and had fairly short muzzels.
Australopithecus: The first human like forms. They are called australopithecines. The name means "Southern ape from Africa". They are lived in thedry open grasslands of Africa about 5 million years ago in Pliocene epoch. Because of a good fossil record, it provides a lot of information about the evolution of man. The features show that Australopithecus was the connecting link betwwen apes and man (Clark, 1960). It shows following characteristic features:
1) They walked erect and had long sized canines and incisors.
2) The brain box was about 600 cc in size.
3) They are about 4 feet tall.
4) They used weapons of bones.
Fossil evidences suggest that there were two species. A. africanus and A.robustus. A. robustus remained unchanged and become exticnt while A. africanus continued to change and evolved to form modern man.
From Human Ancestors till Modern Man:
The first fossil representative of the human genus Homo was H. habilis (the toolmaker). They existed in africa about 3.5 million years ago. The extinct species of Homo are called the prehistoric men.
1) They were about 4 to 5 feet in height.
2) They walked erect and about 40 to 50 kg in weight.
3) They were omnivorous in diet.
4) The cranial capacity was about 700 cc.
5) They made sharp tools of stone and used them for hunting and defense.
6) They were more intelligent and cunning.
7) They led community life in caves.
Homo erectus: They appeared about 1.7 million years ago. The famous fossils of Java Man discovered by Eugene Dubois in Java in 1891 and Peking Man from central China were supposed to belong to the same species Homo erectus. They have cranial capacity of about 750-900 cc (Java man) and 850 - 1300 cc (Pekin man).
1) They were mainly big-game hunters.
2) They used fire and progressed with time using high-quality stone tools.
3) They stood upright and measure about 5 feet high.
4) They used rudimentary language.
5) They are among the first group of fossils to be found in Europe and Asia.
6) They lived in groups in caves.
Neanderthal Man (Homo sapiens neanderthalensis): It was first found in Neanderthal valley near Dusseldorf in Germany (1856) and later in Europe, Africa and W.Asia. It lived about 70,000 to 40,000 years ago, almost all over the world. It shows following features:
1) It resembled modern man but was relatively short, stocky, heavily built.
2) They made tools and used animal hides for clothing.
3) The skull is large with thick cranial walls, prominent supraorbital ridges and a receding forehead.
3) The skull is large with thick cranial walls, prominent supraorbital ridges and a receding forehead.
4) They lived in caves and buried their dead.
5) they used fire for cooking and protection.
6) Fire kept them warm and discouraged carnivorous animals from entering their caves.
7) Their cranial capacity ranged from 1350 to 1700 cc. They have short stature about 5 feet in height.
8) They were capable of communicating each other and had developed primitive type of social life, religion and culture.
9) It is usually believed that they become extinct due to the cold weather or possibly due to the tough competition. Some others have opinion that Cro-Magnons may have killed the Neanderthals. It is possible that the two groups interbred and the Neanderthals lost their identity.
Cro-Magnon Man: Cro-Magnon man appeared in Europe about 34000 years ago. It was as early form of Homo sapiens. The fossils are identical to that of modern human skeleton. They resembled modern man in size and appearance. They were great hunters and used stone tools, weapons, spears and arrows. They were cave-dweller and left behind beautiful pictures of the animals on the cave walls in France and Spain. They used animal hides for clothing. They have long stature about 5-6 feet. They have flat forehead without supraorbital ridges. They have erect posture. Their cranial cavity was about 1600 cc. Prominent chin and narrow elevated nose.
Modern Man: About 1o,ooo years ago man emerged from damp dark caves, built huts of animal skins into the open space and began a sedentry communal life in fixed dwellings. They spread all over the world and became a dominating species. They domisticated animals, learned to plant crops, store food and brought about cultural revolution with its superior intelligence. The brain is believed to be one of the most important characteristics that allows Homo sapiens to dominate the biological world today. The erect posture and bipedal mode of locomotion facilitate the hands to do other works. The hands helped in skilled work, create new things and to write. Brain has superior intelligence and memory, thinking and creative power, coordination of facts and events. Due to above features, brain acts intellectual centre that allows thought, learning, memory and creativity. thus, the hand and brain made the man a super animal and to dominate the biological world today.
Skeleton of Apes:
1) They have small brain box renging from 395 cc (orangutan), 400 cc (Chimpanzee) to 520 cc (Gorilla).
2) Occipetal condyles posterior.
3) Have a semi erect posture.
4) The back bone forms a simple curving arch.
5) Head is buried in the heavy shoulders.
6) Massive jaws without prominent chin.
7) Flat skull with a flat nose.
8) Incisors and canine teeth are larger.
9) Arms are longer than legs.
10) Neack muscles allow less movement of the head on the neck.
11) The thumb does not reach the base of the fore fingers.
12) They have much less ability and cannot manufacture tools.
Skeleton of Man:
1) Man has a much larger brain box about 1200 to 1450 cc.
2) Occipital condyles anterior.
3) Has a fully erect posture.
4) The back bone forms S- shped curve and supports the body weight well.
5) Head is well placed on slender neck.
6) Small jaws with prominent chin.
7) large skull with a raised nose.
8) Incisors and canine teeth are smaller.
9) Arms are shorter than legs.
10) Neck muscles allow more movwment of head on the neck.
11) The thumb extens uo to the middle joint of the fore finger.
12) Man has ability to make and employ tools, speak and write well.
Homology and differences in chromosomes of Apes and Man:
1) The total number of chromosomes in man is 23 pairs, whereas in apes (orangutan, gorilla and chimpanzee) is 24 pairs.
2) The total amount of DNA in a human diploid cell and apes is same.
3) The banding pattern of human chromosomes is very much similar to that of the apes.
4) The homology in the DNA structure, chromosome number and the banding pattern of chromosomes suggests the common ancestry of great apes and man.
Hominid: Any member of the primate family Hominoidae, which includes man, apes and their fossil ancestors.
Ape: Large tail-less monkey is called ape. It is a primate most nealy related to man. Eg: chimpanzee, gorilla, gibbon, orangutan, etc.
Homo: The genus of primates that includes modern man (H.sapiens) and various extict species. The extinct species of genus Homo are called prehistoric man.
Primate: An order of class Mammalia that includes prosimians, monkeys, apes and man.
Anthropoid: The early human ancestors are called anthropoids. They are the ancestors of old world monkeys, apes and humans.
Ramapithecus: A genus of extinct primates that lived about 14 million years ago. Its fossils have been found in Africa and India. Jaw fragments suggest that they chewed from side to side.
Australopithecus: A highly developed age lived in the dry open grasslands of Africa, about 5 million years ago. It is a first human like form, They walked erect and had teeth resembling those of modern man.
Java Man: The extinct species oof Homo (Human). They belong to the species Homo erectus. They appeared about 1.7 million years ago. The fossils of Java Man found in Java in 1891. They are considered as prehistoric man and resemble very much with man.
Peking Man: The extinct species of Homo (Human). They belong to the species Homo erectus. The fossil of Peking man was found in central China. They are alsoconsidered as prehistoric men and resemble very much with man.
Anthropology: The study of all primates , fossil evidence of prehistoric human cultures and all present human cultures.
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