Human Ancestors Till Modern Man

The first fossil representative of the human genus Homo was Homo habilis (the tool maker). They were existed in africa about 3.5 million years ago. The extinct species of Homo are called the prehistoric men.

- They were 4 to 5 feet tall in height.

- They walked erect and were about 40 to 50 kg in weight.

- They were omnivorous.

- The cranial capacity was about 700cc.

- They made sharp tools of stone and used them for hunting and defence.

- They were more intelligent and cunning.

- They led community life in caves.

Homo erectus : During 1.7 million years ago Homo erectus were appeared. They were called Java man. This was discovered by Eugene Dubois in Java in 1891 and Peking man from central capacity of Java man was about 750-900cc and Peking man was 850-1300cc.

- They were mainly big game hunters.

- They used fire and progressed with time using high quality stone tools.

- They stood uprite and about 5 feet tall.

- They used rudimentary language.

- They are among the first group of fossils to be found in Europe and Asia.

- They lived in groups in caves.

Homo sapiens neanderthalensis (Neanderthal Man) : It was first found in Neanderthal valley near Durseldorf in Germany (1856) and later in Europe, Africa and west Asia. It lived about 70000 to 40000 years ago almost all over the world. It shows following features :

- It resembled modern man but was relatively short , stocky and heavily built.

- They made tools and used animals for clothing.

- The skull was large with thick cranial walls, prominent supra orbital ridges and a receding forehead.

- They lived in caves and buried their dead.

- They used fire for cooking and protection. Fire kept them warm and discouraged carnivorous animals from entering their caves.

- Their cranial capacity ranged from 1350-1700cc. They have short stature and about 5feet in height.

- They were capable of communicating each other and had developed primitive type of social life,religion and culture.

- It is usually belived that they become extinct due to the cold weather or possibly due to tough compitation . Cro- Magnons may have killed the Neanderthals. It is also 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 an early form of Homo sapiens. Its fossils are identical as that of modern human skeleton.

- They resembled modern man in size and appearance.

- They were good hunters and used stone tools,weapons,spears and arrows.

- They used to live in caves and have left beautiful pictures of animals on the cave walls in France and Spain.

- They used animals for clothing.

- They were 5 to 6 feet tall and have erect posture.

- They have flat forehead without supra orbital ridges.

- Their cranial capacity was about 1600cc.

- They have prominent chin and narrow nose.

Modern Man :

About 10,000 years ago man emerged from dark caves, built huts of animal skins into open and began a sedentary communal life. they spread all over the world and became a dominating species. They domesticated animals, learned to plant crops,store food and brought cultural revolution with superior intelligence. Brain is believed to be one of the important charcterstics that allows Homo sapiens to dominant the biological world today. They have erect posture. The hands help in skilled work , create new things and write. brain has superior intelligence and memory, thinking and creating power, coordination of facts and events. The hand and brain make man superior animal and dominant species.

EARLY HUMAN ANCESTORS

i. During Eocene epoch Primates came into existence about 65 million years ago. The first primates were somewhat arboreal form like present day tree shrews. The have short nose with flat snouts, grasping hands and feet. These are insectivorous and 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 and have shown progress in using vision more than the smell.


ii. About 60 million years ago during Eocene epoch the prosimians diverged much easier from main stock.


iii. About 50 millions years ago the new world monkeys branched from the ancient primates than after the separation of new world monkeys is called anthropoids line. The anthropoids are the ancestors of old world monkeys,apes,humans. Their fossils were discovered from Oligocene rocks about 36-40 million years old.


iv. In Oligocene epoch about 25-30 million years ago the old world monkeys probably diverged from that anthropoids.


v. The lineage remaining after the separation of the world monkeys is called hominoid line.


vi. The hominids (Dryopithecus or proconsul) are the ancestors of apes and humans.It has been discovered in a rock of Miocene epoch about 20-25 millions years in Asia and Africa. The new world monkeys are native to South America. They possess flat nose, wideb)ly separated and outwardly directed nostrils and long prehensile tail. They lacks opposable thumb and their teeth consists of 3 premolars and 3 molars in each half of jaw. Example- marmosets and spider monkey. The old world monkeys have a narrow nose with closely placed and downwardly directly nose, it is named as Catarrhines , thumb is opposable , have two premolars, show better developed and specialized brain, smaller pinnae and are capable of expressing their emotions by facial gestures. Examples baboons and proboscis.


vii. During the middle of Miocene epoch the subsequent separation of apes and human ancestors occurred between 5 to 10 millions years ago.


The apes evolved on two families they are
a) Hylobatidae : This includes small sized arboreal Gibbons restricted to Asia only.
b) Pongidae : This includes Orangutan, Gorilla, Chimpanzee.

The human evolved on one family Hominidae :
The apes mainly remained on trees and walked on two feet. The main changes in the evolution of human were as follows:

a) The development of an upright postures and bipedal locomotion.
b) The size of body has been increase.
c) The size of canine,incisor teeth and eyebrow ridges reduced.
d) The size of brain have gradually increase for higher intelligency and coordination.
e) The binocular (stereoscopic) vision developed due to shifting of eyes on front size.
f) The development of grasping power in hands i.e thumb opposable to fingers.
g) The arms becomes shorter than legs during the gradual evolution.
h) The chin become distinct and snout absent.
i) Flattering of face have occured.
- Gibbons diverged from the main line about 10 million years ago.
- Orangutans diverged about 8 millions years ago.
- Amcestors of gorilla and chimpanzee separated about 2.3 millions years ago.

viii. During the Miocene epoch about 14 millions years ago the earliest known direct ancestor of man is genus Ramapithecus was found . Its fossils have been found in Aftica , Europe and Asia. The first fossil of Ramapithecus was found in the mid 1930 which included a curved Jaw with an arched palate in northern siwalink hills of India. Similarly, a fragment Jaw of Ramapithicus was recorded in kenya in 1960 about 14 millions years ago. In 1980 Munthe etal was found i.e one of the most important fossils yet collected in Nepal was hominoid tooth on the bank. New fossils discover from the Miocene of Nepal include a hominoid in 1983. The hominoid specimen was a well preserved left upper first molar 10mm long and 10.9mm wide. The tooth was 9-9.5 million years old. It's age was determined by palaemkagnetic studies conducted by the university of Wisconsin-Milliwaukee, USA. Mow it is preserved in the Natural History Museum, Swayambhu, Kathmandu of Nepal.

- They were partially upright and ground dwelling in savannah.
- They were arborial having man like feeding habits.
- They resembled man in having erect posture and small canines.
- Jaw fragments suggest that they chewed from side to side and had fairly short muzzles.

ix. Australopithecus : This is the first human like forms. The name means "Southern ape from Africa" They were live in the dry open grasslands of afeica about 5 million years ago during
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 between apes and man (clark 1960). It shows following features :

a) They walked erect and had long sized canines and incirors.
b) The brain box was about 600cc in size.
c) They are about 4feet tall.
d) they used weapons of bones.

Fossil evidences shows that there were two species. Australopithecus africanus and Australopithecus robustus. A. robustus remained unchanged and becomes extinct while A. africanus continued to change and evolved to form modern man.

HUMAN EVOLUTION

Like other organisms human also evolved over millions of years. The early stages of human evolution are studied by the means of comparative anatomy of fossils and their evidence of the comparative biochemistry of present day human and other mammalian species. human belongs to the class Primates of mammals. The order primates has two suborders

i) Prosimii, includes tree shrews, lemurs, loris, tarsiers etc.

ii)Anthropoidea, includes monkeys,apes and humans. Humans belongs to the family Hominidae.

In 1800s several scientific papers were written on the possible origin of humans. In 1863 T.H Huxley made first attempt to explain the origin of man on scientific basis in his book "Man's Place in nature". Charles Darwin in1871 published a book "The Descent Man" in which he suggested that man was 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. Science that time a great number of fossils apelike creatures were found in Africa and later in Europe and Asia as well. They flourished for many millions years and they are believed to have evolved into modern apes and humans. Now adays it is believed that the ancestors of man and ancestors of great apes decendent from common ancestors and both human and apes evolved along different lines. Today apes are highly specialized forms. Human beings are highly specialised form.

THEORIES OF EVOLUTION

1. Lamarckism ( Theory Of Inheritance Of Acquired Characters) : The theory of evolution was first forwarded by a renowned French naturalist Jean Baptiste De Lamarck (1744-1829). In 1809 Lamarck published Philosophie Zoologique. In which he have explained the changes that occur in the formation of new type. The theory of Lamarck are as follows -

i.Tendency to grow : All the organisms possess the tendency to grow. The internal forces of life tend to increase the size of the parts of organism up to certain limit and the limit of growth is determined by life itself.

ii. Formation of new organs : The formation of new organs or a body part occurs due to the need and want.

iii. Use and disuse of organs : The organic evolution of plants and animals took place by the influence of the environment according to Lamarck. The gradual change of the environment needs change in animals according to the demands on certain organs. Organs which are used more extensively would enlarge and become more efficient and the organs which are not used degenerate and atrophy.

iv. Inheritance of acquired characters : The characters which are acquired during the life time of individual are transmitted to next generation into new species totally different from the original one. New species are evolved after many generations according to Lamarck by acquiring new characters or losing old ones.

Examples: In ducks, swans and other water birds webbed feet developed by constant stretching of the skin of their feet while swimming on the water surface. Giraffes obtained their long necks and tall feet by stretching their neck to browse upon trees as it needed greater height to reach the higher leaves and in the process of reaching leaves necks became longer in successive generations modern giraffe were result.The limbs are absent in snakes and other burrowing animals because there are no use of such organs.

Criticism Of Lamarckism

i. According to Lamarck all organisms have tendency to grow but many plants contradict this principle by showing reduction in size during evolution.

ii. There is no dispute regarding the environment and individual according to the use and disuse of organs but the inheritance of that effect has become a very controversial subject. The theory on which the inheritance of acquired character based was mainly opposed by a German biologist August Weismann (1834-1914). He purposed "Germplasm theory" . According to this theory continuity of inheritance is concern with the germ cell and the somatic cells have nothing to do.

iii. The muscles of the shoulder of blacksmith develops much due to its constant use during hammering but it is not inherited in their offsprings.

iv. The tradition of boaring of ears and nose by women has been continued from centuries but their progeny do not show trace of holes in nose and ears.

Darwin's Theory Of Natural Selection :

An English naturalist Charles Robert Darwin (1809-1882) published his famous book called " The Origin Of Species By Natural Selection" . This theory is based on a mass of accurate observations and prolonged experiments led whole to believe in the doctrine of evolution. Darwin accompanied Adam Sedgewick on an exploration of North Wales. He spent five years (1831-1836) during the Voyage on the ship called Beagle and made extensive Observations on animal and plant life and brought back a lot of explanation for further examination. He found a living laboratory of evolution along the south American Coasts. In Galapagos Island he found many species of given genus confined to a single island. Various islands had different species of finches of different size and he concluded that finches were arrived from the mainland of South America and has undergone profound changes under the different conditions of the individual island. In 1858 Alferd R. Wallace (1823 -1923) also came in same conclusion.

The factors of Darwin's theory of natural selection are

i.

EVIDENCES OF EVOLUTION

1. Structural evidences : The extensive evidence in support of evolution comes from the structural similarities. The related organisms possess homologous structures because of common ancestry. Among the vertebrate, from frog to man, the vertebral column, eyes, ears, brain and the digestive system are constructed on the same basic plan which suggests common ancestry. In plants, the structural similarities in the type of venation, shape of corolla, cohesion or adhesion of stamens among a group of plants suggest common ancestry.

2. Anatomical Evidences : The comparative anatomy of plants and animals provides the strong evidence for organic evolution. The forelimbs of many vertebrates such as amphibians, lizards, birds, bats and man are constructed on the basic plans and includes the same bones in the same positions but they have become morphologically different in the course of evolution. The organs which are similar in structures and origin but performs different function are called homologous organs and the organs which have similar functions but different origin is called analogous organs. for eg - wings of insects and vertebrates. similarly, the study of xylem, development of stele, nature of tracheids and vessels among higher cryptogams, gymnosperms and angiosperms provides additional support to the theory of evolution.

3. Palaeontological Evidences : Palantology is the study of fossils of anicient plants and animals. Fossils is defined as the remains of ancient plants and animals preserved in the rocks or different layers of earth. The study of fossils provided most convincing and direct evidence of evolution. This help us to trace the facts related with the origin, evolution, relationship and increasing complexity etc of different plants and animals in different geological eras of the earth. The surface of the earth consists of layers or strata of rocks formed in different periods. The earliest formed rocks shows most primitive form of life and later form rocks shows fossils of more complex types. Animals are better preserved as fossils as compared to plants and helps in drawing correct conclusions about origin of modern vertebrates. The age of fossils can be determined either by radioactive carbon dating or by the amount lead in the rocks.

4.Evidence from physiology and biochemistry :

i. Protoplasm chemistry : The protoplasm consists of substance like proteins, lipids, carbohydrates, nucleic acids and water, although show great diversity in the form and functions according to the biochemical analysis of the living organisms.This suggests that most of the fundamental property of living things remained intact and variations in certain essential areas appeared according to the use and needs.

ii. Chromosome chemistry : The common structure of chromosomes among the diverse group of organisms suggest a common origin of most of the living organisms.

iii. Enzyme similarities : enzymes such as trypsin is similar and found in animals ranging from protozoa to mammals , whereas amylase is found from sponges to mammals.

iv. Haemin Crystals : The haemoglobin in blood precipitates in crystals when it is treated with glacial acetic acid, they are called haemin crystals. Crystals of all members of a species are similar in shape, size and structure but differ from those of other species. They are different with the classification of animals and confirms their phylogenetic relationships.

v. Hormonal Similarities : All vertebrates show close similarity in their hormones . eg- thyroid hormones is commonly found in all vertebrates. Deficiency of this hormones in frog can be corrected by feeding them on mammalian thyroid tissues which suggests a common ancestry of vertebrates.

vi. Serological test : This test is used in measuring the degree of relationship among different groups of animals and is helpful in establishing their affinities. The thin liquids that remains from blood on clotting is called serum, it contains specific proteins. If the blood serum of an animal injected into blood stream of some other animals, antibodies against the antigens of injected blood are produced. These antibodies destroy the antigens of injected blood serum. Serological tests have shown that man is more related to chimpanzee than to apes, gorilla and baboon. similarly, cats, dogs and bears are closely related, this test can also be done in plants.

5. Evidence from Genetics : In search of new varieties, man is involved in selecting and breeding animals and plants for his own use due to this new species are evolved. Thus the selection and interbreeding of domesticated animals and plants for thousand of years provide model as to how some evolutionary processes operate in nature. Organisms changes with changing environment and many of these variations are heritable. The most important genetic phenomenon that played main role in evolution are recombination and mutation. They generate diversity on which natural selection theory works.

6. Evidences from vestigial organs : Vestigial organs or Rudimentary organs are the reduced and functionally useless structures of plants and animals. These organs were functional and useful in ancestral forms but due to changes in environment and mode of life they become reduced and function less. There are large number of vestigial organs in man. The muscles of the ears which moves the pinna in other mammals like horse are found in reduced form in man, Vermiform appendix which is well develop in herbivorous mammals is present in small diverticulum in man, A fold of the skin in the corner of human eye represents nictitating membranes of reptiles and birds. In kiwi a flightless bird of new zealand the feathers are reduced to almost hair-like and wings are reduced and become useless organs. caudal vertebra which develops tail are present as vestigial organ in man. In plants the abortive stamens of Labiatae and abortive pistillodes of male flowers of cucurbitaceae are well known example of rudimentary structures. Similarly in some member of family compositae, the ray florets have an abortive pistil devoid of any stigma.

TYPES OF EVOLUTION

1. Adaptive Radiation ( Divergent Evolution) : The evolution of different group of organisms from a common ancestral group is called divergent evolution. As the original population increases it spreads out from its center of origin to adapt in habitats and food sources. For eg- Australian marsupials adapted as carnivorous, herbivorous, burrowers, fliers etc.

2. Convergent Evolution ( Convergence) : The process of evolution of unrelated species to resemble each other is called convergent evolution. In this type of evolution the organisms with very different ancestors become more alike because they live in similar habitat. For eg- wings of bats and birds, stream lined body of whales and fishes are analogous structures.

3. Parallel Evolution (Parallelism) : The development of organisms along similar evolutionary paths due to strong selection pressures acting on all of them in the same way. For eg - New world and old world porcupines.

4. Progressive Evolution : This is the type of evolution in which simple forms of organisms develops towards the complex forms and physiological organizations. For eg - evolution of multicellular organisms from unicellular organisms.

5. Retrogressive Evolution : This is the process in which complex forms of organisms develop towards the simpler structural and physiological organizations. For eg - Monocot plants are considered as more advance groups of plants with simple structure and herbaceous habit.

EVOLUTION OF LIFE

The process of change of simpler organisms into complex living organisms due to the gradual changes is called organic evolution. This is almost universally accepted that the present day organisms are evolved by progressive development of simpler organisms to the complex organisms by gradual modifications with time. Life began on the earth after the solidification from molten form and had sufficiently cooled down. During the course of evolution simple form changed into complex form, unicellular forms changed into colonial forms and than multi cellular forms of different tissues. The development of sexuality and alternation of diploid as well as haploid stages of life cycle started. Reduction of haploid gametophytic phase in the life cycle take place. Evolution of new group of plants and animals advances very slowly and it requires millions of years to produced new plants and animals. Evolution proceeds either on progressive or on retrogressive lines, both of these processes of evolution are proceeding simultaneously in nature.

Organic evolution- The gradual development of characteristics of living organism over time is called evolution. The life was originated on the primitive earth by chemical evolution. it was later on replaced by organic evolution. Life in earth was started from the simple and unicellular organisms later on it gradually changed into complex form. Living organisms have evolved through evolutionary process and show diversity and similarities.

First living organism :

1. They were heterotrophic nature.

2.They were prokaryotic like bacteria and were single celled.

3. They were anaerobic in nature.

4. DNA was naked i.e lacks histone protein.

5. Enzymes were present.

6. Soup like sea water was the source of chemoheterotrophic nutrition.

7. The atmosphere was reducing.

8. The respiration was anaerobic and carbon dioxide was evolved.