Origin of Man
(By Dr. Girish Chandra)
Origin of man is one of the most puzzling phenomena of nature. While the fossil records in the case of other animals doubtlessly reveal their ancestry, human fossil records are scanty and full of gaps. There is no written account of our ancestry other than the religious theories that unanimously indicate that Gods descended from heaven and created man in their own image. Man appears to have evolved through natural selection from ape-like creatures that migrated from forests to grasslands and lived as group hunters.
Factors that influenced human evolution
Both Miocene and Pliocene were dry periods of great stress, when sea level went down by about 200 meters and northern and southern hemispheres had huge ice caps. There are indications that fragmentation of dense tropical forests in east Africa initiated the evolution of bipedal hominids from the arboreal apes. The dry period of a few million years put a lot of pressure on the animals living in the shrinking forests and forced them to migrate and adapt to the open grasslands. The evolution of horse, camel, giraffe, and elephant was also triggered by the same factors.
Some groups of apes that were omnivorous and semiterrestrial, faced with intense competition in the forests, started migrating to grasslands. Community living evolved to defend themselves in groups and also to hunt large animals in groups. As the hands were engaged in handling arms and food, they had to walk and run on two legs, giving rise to bipedalism, resulting in the elongation and strengthening of legs. Standing upright in the tropical savannas could also have given them the advantage of scanning horizons for predators as well as potential prey, exposed less of body surface to the perpendicular sun rays and more to the horizontal cooling winds, and freed the hands for carrying stones, sticks, food or infants.
Manipulation of objects by hand put a lot of pressure on brain, leading to its enlargement and increased intelligence. As these migrants continued to live in grasslands and perfected their bipedal locomotion and use of hand for more complex jobs, their brain increased in size and capacity. Later, they started living in caves for protection and probably developed a language for communication. Australopithecus was such a creature, which lived socially in caves, made stone tools and hunted animals. Eating cooked food led to the reduction of canines, shortening of jaw and simplification of teeth. Human evolution is an example of specialization in brain’s ability, achieved due to manipulative skills of hands, strategic group hunting and communication in social groups.
Fossil Records of human phylogeny
Explosive primate radiation took place in the early part of Coenozoic era, in Palaeocene and Eocene epochs. Primitive monkeys and primitive anthropoid apes made their appearance in the Oligocene epoch, about 35 million years ago, thus setting the stage for further hominid evolution. However, fossil records depicting human evolution are incomplete and fragmented and do not give a clear linear picture of human phylogeny.
Parapithecus was a primitive primate ancestral to man, apes and monkeys. It was very small squirrel-like earliest primitive monkey having tarsier-like appearance. The jaw was conical, the two halves converging at an angle of 33 degrees. These creatures were probably adapted for arboreal mode of life and had opposable thumb, forwardly directed eyes and reduced snout.
Propliopithecus fossils were discovered from Fayum deposits in Egypt that comprised of a lower jaw with teeth. The jaw is smaller and more pointed than that of a gibbon, prognathous and deep. Canines were smaller and bunodont grinders had 5 bulbous cusps as in apes and man.
Limnopithecus first discovered by Hopwood in 1933 from Kenya is represented by several fragments of mandibles, teeth and limb bones. The dentition is gibbon-like but limb bones are unspecialized and a combination of monkeys and gibbons.
Pliopithecus is represented by several well preserved fossils from Egypt and Europe. It shows affinity with pongids but the mandibular symphysis is longer and more prosimian type. A shallow simian gap is present. Body is gibbon-like in the morphology of pelvis, vertebrae and sternum. Limb bones are surprisingly primitive, resembling those of prosimians while the general body proportions are like those of monkeys.
Dryopithecus (=Sivapithecus) (=Proconsul) was ancestral to Orangutan, chimpanzee and gorilla and resembled gibbon in stature. Most of the fossils are represented by jaw fragments and teeth, with few exceptions such as a humerus and an ulna from France and a femur from Germany. The three genera, Dryopithecus, Sivapithecus and Proconsul have been placed in the subfamily Dryopithecinae. Arms and legs were of same length and posture was semi-erect. Skull lacked the well-developed crests and massive ridges characteristic of modern apes. Dental arch was parabolic and dentition more man-like but canines were larger and lower premolar is sectorial. It was a brachiator, swinging with arms on tree branches.
Sivapithecus is believed to be the direct ancestor of Ramapithecus, whose fossils have been recovered from the same deposits in the Siwalik Hills and date from 17 to 8 million years old.
Sugrivapithecus fossils were discovered from Siwalik Hill by Lewis in 1934 and are represented by fragments of jaw and teeth. The small size of teeth and canines and simplified molars suggest a transitional stage to hominid type of dentition.
Gigantopithecus remains have been recovered from Siwalik Hills. Reduction of front teeth and canines shows hominid tendencies but the jaw was massive and premolars and molars were large. Jaw allowed grinding sideways motion. It was larger than gorilla, a terrestrial herbivore and lived in open grasslands.
Lufengpithecus fossils recovered from China reveal a highly sexually dimorphic hominoid, having distinctly smaller females and considerably larger male of the size of a chimpanzee.
Sahelanthropus tchadensis. A cranium, jaw fragments and several teeth were discovered from Chad in Africa by Michel Brunet et al. (2002). The 6-7 million year old skull resembles that of a chimpanzee from the posterior side but on the front side is Australopithecine in character.
Ramapithecus (=Kenyapithecus)(=Bramapithecus) fossils of fragments of an upper jaw and teeth were found in 1932 from Haritalaya Nagar in Himachal Pradesh in Siwalik Hills in India by G.Edward Lewis. In Kenya L.S.B. Leakey (1955) discovered a few teeth and jaw fragments of the same species. Canines were small and grinders had low cusps but coated with thick layer of enamel. Brahmapithecus is represented by lower jaw only. Face was short and jaw allowed sideway motion. Dentition was human and palate arched. Incisors and canines were small, permitting lateral chewing. Grinding teeth were large and broad with thick enamel coating, suggesting herbivore diet of grass, seeds, roots and perhaps raw meat.
Ramapithecus fossils show advancement in morphology over Sivapithecus that brings it closer to Australopithecus. They probably originated in Africa and later migrated to Eurasia.
After Ramapithecus no fossils are available for almost 10 million years, which is a big gap in phylogeny of man.
Oreopithecus fossils were discovered from lignite mines in Italy. One nearly complete skeleton of the abominable Coal Man was unearthed from Italy and later about 200 fossils were collected from Europe and East Africa. Dentition was human, canines were small and face short but premolars and molars were ape-like. Pelvic girdle was broad, indicating erect posture. It was an herbivore living in swampy areas.
Australopithecus africanus, “the southern ape” is the most primitive of Australopithecines that existed between 5.5 and 2 million years ago. Fossil of a 5-year old boy (Taung baby) was discovered from South Africa by Prof. Raymond A. Dart in 1924. It was 5 feet tall and walked erect. Vertebral column had a lumbar curve and pelvis was broad. Foramen magnum was placed under the skull. Teeth human and dental arch smoothly rounded. Palate seems to be shallow anteriorly and deep posteriorly. Canines were small and simian gap absent. Premolars and molars greatly enlarged relative to incisors and canines. Cranial capacity was 450-700 cc. Face was prognathous with long palate but less prominent eyebrow ridges and without chin. Orbits were large and rounded. Nasal bones were flat, giving the short face a dish-shaped appearance. Australopithecus occurred in two forms: a small gracile and a larger robust form spread in Tanzania, Kenya and Ethiopia and South Africa. Many scientists are now using the generic name Paranthropus, which was originally given to the species robustus, to refer to the robust forms of Australopithecus, which includes robustus, boisei and aethiopicus.
Australopithecus afarensis was a gracile form and probably a descendant of A. africanus. One almost complete skeleton of a female named “Lucy” was discovered from Afar (Ethiopia) by Donald Johanson in 1973. It was dated at 3.5 million years. It was about 5 feet tall and walked erect and had an arched foot to support the bipedal gait. Cranial capacity was 400-500 cc. Canines were small with thick layer of enamel and molars were designed to grind tough material.
Australopithecus garhi. A fragmentary skull was excavated in 1997 by Asfaw and White from Bouri village in the middle Awash region in Ethiopia and dated at 2.5 million years. The fossil was found near antelope bones which were butchered by it using specialized stone tools that were carried with it from other places where the raw material for it was available. The stone hammers, axes and blades enabled this species to exploit a broader range of habitats and prey to obtain energy rich food that was necessary for the enlargement of energy consuming brain.
Australopithecus anamensis fossils, discovered near Anam lake at Kanapoi and Allia Bay in Kenya by Meave G. Leakey, were dated to about 4 million years. Skull fragments and teeth were similar to those of earlier species but arms and leg bones were more advanced and indicative of bipedal gait.
Ardipithecus ramidus is represented by 21 specimens found near Lake Turkana and from Aramis in the Awash Valley in 1995. Dated back to 4.4 million years, it perhaps walked erect. It is believed to be a sister species of anamensis.
The following three species were robust forms of Australopithecus, sometimes identified by the separate generic name, Paranthropus, as they seem to have descended from a common ancestor.
Australopithecus robustus (=Paranthropus robustus) was first discovered by Robert Broom in 1939 from South Africa and dated to 1.5-2.0 million years. It is characterized by heavily built skull having rounded appearance, higher vertex and a bony keel on the top for the attachment of large jaw muscles. Forehead was slanting and eyebrow ridges massive. Foramen magnum and occipital condyles were anteriorly placed. Dental arch was rounded and massive without diastema and simian shelf. Incisors and canines were small and spatulate, while premolars and molars were very large.
Zinjanthropus boisei, the “Nutcracker Man” was discovered by L.S.B.Leakey in 1959 from Tanganyika in East Africa and at Olduvai gorge in Tanzania, along with stone tools, and was dated to about 1.7 million years. It had massive jaws and teeth, with small incisors and large canines. There is cerebral enlargement with a cranial capacity of 600 cc. Face was protruding and forehead high, having prominent eyebrow ridges. Nasal spine was elevated.
Australopithecus aethiopicus was discovered by Allan C.Walker from Lake Turkana in Kenya and is represented by a 2.5 million years old blackish skull. It is related to A. robustus and boisei and may be their ancestor.
Homo habilis, called the “Able Man” lived 1.85-2.6 million years ago and walked erect. Fossils were discovered by Louis Leakey in 1959 from Olduvai Gorge in Tanzania, where later several teeth, jaw and skull fragments were discovered. Its premolars and molars were smaller and anterior teeth larger. It was 140 cm tall, with cranial capacity of 700 cc and human teeth. It was a habitual biped and probably ancestral to all Homo. It hunted small animals and was a scavenger of large carcasses. Face was less prognathous and nasal bones convex. It was closely related to A. africanus but was more advanced in features and occupied similar ecological niche.
Homo erectus fossil remains dating from 1.9 million years to about 250,000 years discovered from Java, China and later Europe and Africa are collectively known as Homo erectus, the archaic man that had larger brain and used stone hand axes. Supraorbital ridges are prominent, with an indented area behind them. It had massive face that projected below and heavily built mandibles, without a chin that were moved by strong masseter muscles. Teeth are similar to ours but incisors are slightly larger and shovel-shaped having enlarged pulp cavity, an adaptation for hard chewing. They knew the controlled use of fire to cook food and keep them warm. The use of fire was perhaps necessary to occupy caves that were inhabited by large carnivores. The mean cranial capacity was 1020 cc, which was approximately twice the size of australopithecines but only three-fourth of Homo sapiens.
Homo ergaster, considered the African counterpart of Homo erectus, was discovered from Koobi Fora in Kenya and dated to 1.6 million years. In 1954 hominid remains from Algeria and Morocco showed affinities with the Chinese form of Homo erectus. After 1970, Richard Leakey unearthed fossils from the eastern shores of Lake Turkana and one complete skull from Koobi Fora that is believed to be the earliest Homo erectus fossil in Africa.
Pithecanthropus erectus (Java Man) was discovered by a Dutch army officer, Eugene Dubois in 1891. Skull cap, few teeth and a femur are known. Forehead was low and supraorbital ridge. Cranial capacity was 775-900 cc. Height was about 5 feet and it walked erect efficiently. Bones of the skull were extraordinarily thick. Face was prognathous, chinless and skull flat on the top and projected behind.
Sinanthropus pekinensis (Peking Man) was first reported by a Canadian Professor, Davidson Black in 1927, who found only one skull. It was similar to Java man but skulls were small and cranial capacity 850-1200 cc. Eyebrow ridges were stout. Stone tools of varied designs were also found along with bones of large animals and pieces of charred wood and bones. It walked erect.
Homo heidelbergensis is represented by a single jaw recovered from a sandpit near Heidelberg in Germany in 1907. Lower jaw was massive and chinless but teeth were stout and human. The anatomical features were more advanced than those of the African and Asian forms of Homo erectus. They were low-browed hominids having thick bones and robust skeletons and perhaps represented earlier stage of Homo sapiens.
Steinham Man is represented by a complete skull found in 1933 from a gravel pit at Steinham site in Germany. Its age is estimated to be same as for Swanscombe man, from the second interglacial period. Cranial capacity was 1070 to 1175 cc. Fore head was high but eyebrow ridges were heavy and the nasal opening broad as in Neanderthals.
Swanscombe Man is known by two pieces of the skull roof consisting of one occipital and two parietal bones that are unusually thick. Skull is broad at the back but the occipital region is not projected behind as in Neanderthals. Cranial capacity was 1300 cc. Some stone tools were also discovered from the same site.
Fontechivade Man fossils are from France. Skull bones were thick and cranial capacity about 1400 cc. Supraorbital ridges were not prominent.
Solo Man is known by partial skull and 2 femur bones discovered from Solo river in Java in 1933. Forehead was low and eyebrow ridges heavy. Cranial capacity was 1300 cc.
Rhodesian man was discovered in Rhodesia (= Zimbabwe) in 1921. Cranial capacity was 1300 cc. Eyebrow ridges were heavy and jaw was projecting forward, although the dental arch was parabolic. The Rhodesian man was about 6 feet tall, neanderthaloid in appearance and is now regarded as a subspecies of Homo sapiens.
Neanderthal Man (Homo neanderthalensis) is known originally from Neander Valley in Germany. Later, fossils of about 200 individuals were unearthed from 70 sites in Austria, China, France, England, Germany, Greece, Italy, Iraq, Israel, Java, Russia and Yugoslavia. The species lived between 200,000 and 30,000 years ago. The average cranial capacity was 1450 cc, which is greater than in modern man, but the brain was large posteriorly and ventrally. They were stout and powerfully built people, weighing over 80 kg and having an average height of 5’6”. Long bones were thick, slightly curved and had large areas for muscle attachment. Forehead was low and slanting, eyebrow ridges were heavy and cheek bones were large. Nose was broad and chin was absent. Stature was robust and completely upright. Teeth were large. They were cave dwellers living in the most adverse environmental conditions and used fire, made stone tools and crude carvings and practiced burial. There is strong evidence of ritualistic practices, religious beliefs and ceremonious burials. The classic Neanderthals come from fourth interglacial period in Europe and had stocky and rugged stature, broad nose, stout mandible, projecting occipital region and no chin.
Causes of extinction of Neanderthals are not clear. The most plausible explanation is that a more advanced species, Cro-Magnon man evolved in Africa and migrated to Europe about 40,000 year ago and exterminated the Neanderthals. However, recent findings indicate that extinction of Neanderthals was not so fast and that it coexisted with Cro-Magnon for about 10,000 years and perhaps produced viable hybrids. That leads to another possibility that they must have interbred with the new and more advanced populations immigrating from Africa, producing the modern man. But a study of mitochondrial DNA sequences recovered from the skeleton of a Neanderthal suggests that modern humans are closely related to each other than to Neanderthals.
Cro-Magnon Man (Homo sapiens fossilis) was a contemporary of Neanderthal man and lived in Europe during the upper Paleolithic period (about 40,000-10,000 years ago). Large number of fossils was found from a cave in Cro-Magnon in France. Male was 6 feet and female 5 feet 6 inches tall. Skull was like modern man, with a distinct chin, flat eyebrow ridges and orthognathous face. Teeth and jaw were distinctly like modern man. Cranial capacity was about 1500 cc., same as that of modern man. They showed technological advancement in using bones, antlers, stones etc. to make tools and spears and also specialized tools such as needles, harpoons, engraving tools, blades, soft hammers and heat-treated flints. They used ornaments for the first time and performed rituals. Coloured pictures of animals in the deepest parts of the caves and also carvings of wood, ivory and stones point to their advanced skills. They apparently knew the use of fire but did not practice agriculture or domestication of animals. They also buried their dead with some rituals.
Both Cro-Magnon and Neanderthal man lived during the glacial period, when their main occupation was hunting wild animals for food, which they cooked on fire in caves. Cro-Magnon had better intelligence and advanced tools and arms and hence perhaps exterminated Neanderthal. Towards the end of glaciations, they probably migrated to warmer parts of the world and settled down in colonies along the rivers to practice agriculture and domestication of animals, which gave them sure and constant supply of food. Evolution of man after that was very fast as compared to the earlier slow pace of evolution during Pleistocene epoch.
Homo floresiensis. Also named as Homo hobbit, the discovery of the little man from limestone cave at Liang Bua on the Indonesian island of Flores by the Australian archaeologists surprised everyone. The 18,000 year old fossils were only a meter tall and had cranial capacity of only 380 cc. These tiny people lived in isolation in the far-flung Indonesian island where giant rats, tiny elephants, Komodo dragons and other large lizards were abundant. The isolation forced the species to remain small-sized and live in holes in the ground to escape giant predatory lizards and hunt giant rats for food.
The molecular evidence. Mitochondrial DNA is inherited maternally through the cytoplasm of the egg which contains about 100,000 mitochondria (sperm contains insignificant amount of mtDNA, only about 50), and is not subjected to the same selection pressure as the nuclear DNA. The rate of mutation in mtDNA is ten times faster than nuclear DNA and is constant and hence can be measured to reveal a relationship between two species that emerged from common ancestor. Cann et al. (1987) analyzed 144 mtDNA samples from human groups of different origin and estimated the age of common ancestor as 150,000-290,000 years. Linda Vigilant et al. (1991) studied mitochondrial DNA of 189 people from different regions. Their direct maternal ancestry was found to converge to a single female in Africa called “mitochondrial Eve” that lived between 1,66,000 and 2,49,000 years ago.
Data on amino acid residues indicates that chimpanzee and gorilla are genealogically closer to man than to other apes. The fusion of acrocentric chromosomes, which is called Robertsonian translocation, has perhaps taken place, which reduced the number of chromosomes from 48 in apes to 46 in man. Such chromosomal rearrangements and also pericentric and paracentric inversions alter the metabolic pathways and thus produce reproductive isolation.
Single origin versus multiple origin of man
Molecular evidence seems to support the African origin of humans and then their migration to other continents to develop racial differences. All non-African mitochondrial DNA sequences are only variants of the African sequence, and African populations possess the maximum mtDNA variability suggesting their ancient character. A study by Hammer and co-workers of Y-chromosome of more than 1500 individuals from all continents also points to the African origin of man. Human populations all over the world are basically similar in anatomy and genetic composition and hence must have had a single origin in Africa.
Multiple origin hypothesis or multiregional proposal, on the other hand, suggests that all human populations in different continents evolved in parallel over long periods from Homo erectus. Hominids migrated out of Africa much earlier than the subsequent origin of modern man about 100,000 years ago in different geographic regions of the world. Fossils from the Chinese and Australian regions show continuous and independent progression from the Homo erectus stage to the present. Human ancestors were highly mobile creatures and hence constantly exchanged genes between populations to break the reproductive isolation and keep genetic variability to the minimum.
Cultural and social evolution of man
Modern humans, being highly social, learn from their experiences, share these experiences with the others and modify their behaviour based on constant learning. Unlike other animals, they are also capable of modifying their environment to suit their needs and keep considerable control over it. An important difference between the genetic exchanges and cultural exchanges is that the former can take place between parents and offspring while the latter can take place among the unrelated individuals. Therefore, while the biological traits are transmitted vertically within the lineages, cultural traits are transmitted both vertically and horizontally within lineages or among the unrelated individuals. Cultural evolution is therefore much faster than the genetic evolution. While the cultural evolution follows Lamarckian mode of inheritance, the biological evolution is driven by natural selection in which information is transmitted through DNA and the mechanisms of heredity. Cultural evolution is independent of genetic system and can take place without making any change in the genes.
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