Introduction
Terminology or the application of appropriate word expressions in specific context to the subject; Taxonomy refers to that branch of science which is concerned with systematic classification of the organisms and the Chronology is the arrangement of the events or fossils in the order of their occurrence. In the present module, the terminological, taxonomy and chronology problems of human fossil ancestors were discussed. The geological time scale starts with the formation of the earth, some 4.6 billion years ago. The first and longest span of time was the pre-Cambrian, where forms of life were small, simple and softbodied. The onset of Cambrian about 570 million years ago marked the rise of shelled animals in the sea. Then followed the “ages” of the fish, Amphibians and Reptiles, culminating in the domination of land by the dinosaurs, from about 200 to 65 million years ago.
Mammals first appeared more than 200 million years ago, but were overshadowed by the reptiles. However, some 65 million years ago all the dinosaurs – as well as other groups of reptiles on land, in the sea and in the air, and certain other animal groups and many plants too – became extinct over a relatively short period. This was only one of several “mass extinctions” that have occurred through geological time. The extinction marked the beginning of the Tertiary period and the Age of Mammals. The Tertiary is divided into epochs, and development in the primate group can be traced from the fossils they left in the rocks formed during the time. The first hominids (members of our family Hominidae) crop up in the fossil record less than million years ago. Mammalian evolution covers only about 4 percent of the Earth’s entire history, and humans have been around for only 0.1 percent of the history of our planet The quest for our ultimate origins begins with the origin of life itself. The earth is about 4.6 billion years old. Fossil evidence shows that small, simple organisms were living at least 3 billion years ago. A great deal of evidence supports the notion that all present day organisms are related to each other, and these forms as diverse as slime molds and elephants, oak trees and beetles, roses and humans – ultimately arose from a single common ancestor, some 3.5 billion years ago. This means that a single evolutionary tree or phylogeny, relates all organisms, living and extinct. Biologists and palaeontologists assume that life evolved from its simple beginnings through a succession of stages, as represented in the fossil record, toward the present day diversity of some 10 – 30 million species. This does not mean that today’s diversity is in some way the destiny or the end point of evolution; there has been great diversity in the past, and there may be in the future.
2. Human Fossil Ancestors The course of human phylogeny or the human biological evolution like other mammals can be followed only from the fossil records. Though the fossil records are fragmentary, the paleoanthropologists have been able to piece them together and draw them an almost complete phylogeny of primates and of modern man, Homo sapiens sapiens. The early stages of human biological diversity can only be studies by comparative anatomy of fossils and also by comparative biochemistry of present day humans, apes and other primates. Information on the later stages in human evolution are based on artifacts that include stone tools, pottery, fire – hearths and the fossils of other animals along with human fossils.
The fossils of pre-human and ancestral human forms are obtained from widely diverse regions of Africa, Asia and Europe which indicates that man’s centre of origin was probably in Asia and Africa. More precisely human must have been originated from central Asia because the oldest known fossils have been obtained from Asia, China, Java and India (Siwalik hills); the number of domesticated animals and plants is maximum in Asia; A number of migrations of animals have occurred in the past from Asia; Asian culture appears to be the oldest culture; the climatic conditions in Asia and nearby places were most conductive for human evolution and rich fossil beds are discovered from rift valley in East Africa, where Hominid fossils have been found. These areas are – Olduvai Gorge, Lake Victoria and Lake Natrona in Tanzania and Lake Turkana in Kenya. Through the fossils records, it can deduced that the last and most important hominid from Miocene is Ramapithecus and through evolutionary processes it evolved to Homo sapiens sapiens of modern times.
2.1. Ramapithecus
2.2. Australopithecines
2.2.3. Chronological Implications
These Pliocene and Pleistocene fossils have shown both hominid and ape-like features. However the hominid features are overwhelming. The presence of ape-like features can be accounted for by way of common inheritance from a hominid or pongid ancestor. The hominid characters however can be accounted for by way of independent acquisition demonstrating and highlighting the fact that these fossils were on a direct line of human evolution and not pongid line. According to Donald C. Johnson and Timothy White, the East African fossil Australopithecus afarensis split into two branches, an australopithecine line represented by A.africanus, P.robustus, P.boisei and a hominid line represented by Homo habilis, Homo erectus and Homo sapiens. This split was supposed to have happened 3 million years ago. The australopithecine line progressively became robust. This pattern generally called two-branch theory. According to this two-branch theory, A.afarensis gave rise to A.africanus 3mya, of the same height, living upto 2mya. Next arrived A.robustus which showed marked increase in robustness of body, face, jaws and teeth and it has lived upto 2.3 to 1.8 mya. Finally the last and the most robust form A.boisei lived in east Africa from roughly 1.8 to 1 million years ago. The second branch of the model, the Homo line, also shows a shortening of the face but there is a marked decrease in the size of both the cheek teeth and the front teeth. There is a massive increase in the size of the brain. This line begins with a transition from A.afarensis to H.habilis, the first hominid who made and used tools and lived in Africa from 2 to 1.5 mya. However, we can conclude that hominid evolution may not have been so simple, isolated and clear-cut in its operation. Instead, there is a possibility that three or more hominid lineages may have been evolving and interacting with each other. The two-branch theory was widely accepted till the discovery of a new type of hominid skull – Australopithecus aethiopicus, in northern Kenya in 1985 by Alan Walker. This skull had massive teeth and ape like brain. Thus the revised theory holds a three line evolutionary sequence, one to A.boisei line, second to Homo and third to africanus, robustus line having A.afarensis as the common ancestor. The discovery of Australopithecine – A.ramidus has added a new dimension to the three branch theory. It holds that A.afarensis is the common ancestor for Homo, P.boisei and P.robustus but it itself evolved from A.ramidus. With overspecialization of diet, competition for food with H.habilis and the later’s predation along with H.erectus led to the extinction of the australopithecine group
2.3. Homo habilis
2.3.2. Chronological Implications One of the main criteria for inclusion in the genus Homo was brain size. Different authorities had different threshold sizes ranging from 700 – 800 c.c. Most australopithecines were around 500 c.c., while Homo erectus was above 1000 c.c. For some authors, a brain size of more than 600 c.c. would suffice for inclusion in Homo along with other features indicated by the fossils such as upright posture and bipedal walking, and a precision grip in the hand. The first H.habilis specimen had a brain size estimated at 680 c.c. In the mid 1960s, many people thought it probable that Homo erectus had evolved from some type of australopithecine. Therefore, it would be natural to find fossils representing transitional form – the result of evolution in action. Rather than create a separate species, this new form should be placed either with its predecessors, the australopithecines, or with its successor, Homo erectus. According to Le Gros Clark, Homo habilis can be easily accommodated within A.africanus. There were plenty of other opinions about were Homo habilis fitted into the hominid evolutionary tree. Leakey long held the view that our modern species was in fact direct descendents of Homo habilis. In 1972, Richard discovered a skull at Koobi Fora which had a cranial capacity of 800c.c. A brain size of this surely meant the creature to be a member of genus Homo. Till today more than 20 Homo habilis fossils have been found. Besides having a bigger brain than australopithecines, Homo habilis also had a higher brain to body ratio. Compared to apes, the temporal lobes which deal with memory and other mental functions are more developed; so are the parietal lobes which analyze information coming in from senses and the speech processing area is also developed. The version of our evolutionary tree in which A.afarensis gave rise to H. habilis, which evolved into H.erectus, which in turn produced homo sapiens, has an appealingly neat straight line. But standing back from the main habilis time period about 1.9 – 1.6 mya, brings various complications. By 1.6 mya, another human species had appeared. The taller, long legged, bigger brained Homo erectus. If habilis did evolve into erectus, could such a great evolutionary change have taken place so quickly? One possibility is punctuation – a rapid burst of change in the type of evolutionary process known as punctuated equilibrium. The time between 2 and 1.5 mya has been called the “crucial humanizing period”. Recent fossil finds from this time have widened the debate as to how many species of hominids lived in Africa then, and who evolved into what. More fossils may serve to clarify the picture or further to confuse it.
2.4. Homo erectus
2.4.2. Chronological Implications What caused the biological advance that led early Homo to evolve into Homo erectus? One of the most plausible theories has been put forward by Grover S. Krantz in 1968. He points out that contemporary hunting and foraging groups with Stone Age technologies engage in what he terms persistence hunting. One of the conspicuous aspects of the transition from the australopithecine stage to that of Homo erectus is the dramatic expansion of the size of the brain and the development of the cortex. Krantz suggests this evolutionary development underlies an improved memory and thus provided a selective advantage to those individuals who were consequently better able to keep memory images in their minds to motivate their hunting behaviour. One does not have to stress persistence hunting as a selective pressure for the brain expansion and the increase in its organizational complexity that marked the transition to Homo erectus. Nevertheless the incorporation of regular, cooperative hunting into a primitive social system must have had a profound and extensive impact. And not only social behaviours – the body itself quite probably changed significantly. These changes included physical adaptations to day time hunting like increased pigmentation of the skin, loss of fur on the body and increase in the number of sweat glands. Thus, we may, with assurance, refer to Homo erectus as an extinct ancestral form of human being.
2.5. Neanderthal Man
2.5.2. Chronological Implications The Classic Neanderthals seem to have been disappeared between 35,000 to 40,000 years ago, as we have no fossil evidence thereafter. According to one view, they are believed to have been driven out by the migrations of advanced modern forms which are now referred to as Homo sapiens sapiens. However, some authors believe that Neanderthals gave rise to modern man. Brose and Wolpoff are of the opinion that there is a continuous development of Neanderthal man to Homo sapiens sapiens. They have noted that in certain sites there are continuous sequences showing a gradual transition in cultural remains from Neanderthal man to modern man. They however feel that the gradual increase in the number of specialized tools during the period indicated more efficient technology which developed by the end of the Neanderthal period
2.6. Rhodesian Man
2.6.2. Chronological Implications In 1921, Woodward on the basis of the position of foramen magnum considers it to be human and assigns these to Homo rhodesiensis. However, some feels that they did not have erect posture as is indicated by the pelvis and assigned it to Cyphanthropus rhodesiensis. This connection however has not been accepted. Von Bonian feels that the skull, pelvis, femur and tibia indicate erect posture and places the Rhodesian man near the point of divergence of the Neanderthal and the modern man. In the opinion of Boule, Neanderthal man, Rhodesian man and modern Australians had a common origin. Rhodesian man may be the African variety of Neanderthals. In the opinion of Hooton, there is sufficient likeness between Neanderthal and Rhodesian man so as to regard the latter as a variant of the former. In certain features Rhodesian man is inferior to Neanderthals and even to Pithecanthropus.
2.7. Homo sapiens
2.7.1. Cro- Magnon Man In 1868, M. Louis Lartet excavated the rock shelter of Cro-magnon on the banks of Vezere in the village of Les Eyzies. This site has yielded several human skeletons. There were strata containing hearths and implements of Aurignacian culture. The skull is massive and large in every dimension. The skull is dolichocranial and exhibits a pentagonal contour. The cranial capacity about 1660 c.c. The forehead is broad and the occiput bulges behind. The face is relatively flat and very broad. The cheek bones are large and protruding, nose is narrow, long and high. The maxilla exhibit pronounced prognathism. The chin is prominent. The forearms are long in comparison to upper arms. Another important feature is a type of flattening of the thigh bones called Platymeria and also side to side flattening of the shin called Platynemia. This is attributed to the habit of walking with the knees bent. The muscular impressions are strongly marked. 2.7.2. Grimaldi man Grimaldi fossil remains are referred to as European Upper Paleolithic. The discovery was made in a cave near Mentone in Italy. In one of the caves, called Grotte des Enfants, two skeletons were found in 1901. On the basis of cranial morphology, the Grimaldi skulls are believed to have Negroid features. The cranial capacity is around 1454 c.c. The skulls are long, narrow and high. The brow ridges are feebly developed as in the Negroid crania. The forehead is straight and well developed and slightly bulging. The skull presents a regular elliptically shaped contour with flattened parietal eminences. The face is narrow and short. Nose is depressed at the root, the bridge is low and broad suggesting that the nose is Platyrrhine. The lower jaw is strong with its body very thick. The chin is not greatly developed. The forearm and the leg are very long in relation to the Upper arm and thigh respectively. The shaft of the femur has a pronounced curvature and is strongly bent. The Grimaldi material is believed by many anthropologists as definitely Negroid and they are commonly accepted as a good evidence of Negroid race in Europe during Aurignacian times.
2.7.3. Chancelade Man The name is derived from a rock shelter near Chancelade where the discovery was made. The deposits yielded the typical fauna and implements belonging to the Magdalenian period. The skeleton lay on its left side in the deepest stratum with its arms folded on its breats and knees doubled up against the body. The body is powdered over with red ochre. The skull of the Chancelade man resembles the crania of Eskimos. It is long and narrow. Supra orbital ridges are slightly developed with forehead bulging and rising vertically. The cranial capacity estimated is around 1530 c.c. face is long and moderately broad. The cheek bones are prominent and strongly developed, which give a flat appearance to the face. The nose is long and narrow and the nasal bridge is broken. The post cranial skeleton indicates that long bones are massive and strong. The muscular impressions are well marked indicating a muscular body. The stature was short. The upper are longer unlike Europeans. Femur is slightly bent. The shaft of the tibia has a flattening in the transverse direction and is slightly Platynemic. Foot is large with first metatarsal distinctly separated from second toe like in Neanderthal man.