19 The Dispersion of Modern Humans-Molecular and Morphological Patterns of Relationship

Dr. Vijeta Dr. Vijeta

Contents:

• Introduction
• Traditional Studies of Race
• Molecular Patterns of Relationships
• The Peopling of Pacific
• Morphological Patterns of Relationship
• Conclusion
• Summary

Learning Objectives:

1. To understand about the dispersion of modern humans

2. To understand about the molecular patterns of relationship.

3. To understand about the morphological patterns of relationship.

Introduction

The biological variety of living human populations from the beginnings of anthropology has been approached through the study of race. For almost two centuries following Linnaeus, anthropologists attempted to define discrete units of humanity, and to find criteria for distinguishing among these ‘races’ as sharply as possible. Individual’s best conforming to such criteria were viewed as ‘pure’. All this happened before the emergence of genetics (Jones et al., 1992). Human populations in different parts of the world have adjusted to the physical environment in various ways, but surprisingly little is known of the adaptive significance of these physical differences. Such variation must be an outcome of the evolution of modem Homo sapiens, although we have learned little about just how this happened.

Traditional Studies of Race

There have been several attempts to categories the variety of present humans. Many of these are unnecessarily pro-crustean, but have some value in purely descriptive terms. A typical classification based on human visible variation is as follows: Caucasoid, from northern Europe to northern Africa and India. These are depigmented to a greater or lesser degree. Hair in males is generally well developed on the face and body, and is mostly fine and wavy or straight. A narrow face and prominent narrow nose are both typical. Negroid (or Congoid), in sub-Saharan Africa. Skin pigment is dense, hair woolly, noses broad, faces generally short lips thick, and ears are squarish and lobeless. Stature varies greatly, from pygmy to very tall (in the latter the face is long). The most divergent group is the Khoisan (Bushman and Hottentot) peoples of southern Africa. Mongoloid, found in all parts of Asia except the west and south (India), in the northern and eastern Pacific, and in the Americas. The skin is brown to light, hair coarse, straight to wavy, and sparse on the face and body. The face is broad and tends to flatness. The eyelid is covered by an internal skinfold known as epicanthic eyefold amongst this population but such folds are less marked or absent in other races. The teeth often have crowns more complex than in other peoples, and the inner surfaces of the upper incisors frequently have a shovel appearance. The Chinese, Koreans and Japanese are the ‘typical’ populations and have probably shown considerable expansion in historical times. In central and northeastern Asia and among hunt the flatness of face and nose is still more marked. In more marginal populations, such as the Ainu of Japan, aboriginal Taiwanese, Philippine Islanders, Indonesians and Southeast Asians these traits are less marked. The same is true of Polynesians and Mieronesians. In American Indians, the face is usually broad but nasal bridges are apt to be more prominent relative to the eyes; the teeth are especially complex in pattern and shovelled incisors are particularly prevalent. Australoid, the aboriginals of Australia and Melanesia. Skin is dark; hair predominantly wavy (Australia) or frizzy (Melanesia), with biondness in children (lost in adulthood) being common throughout. The head is long and narrow, the forehead sloping with prominent brow ridges, and the face has a projecting jaw (Jones et al., 1992).

Molecular Patterns of Relationships

Genetic analysis became possible with the discovery of systems of blood groups. This work was the first to emphasize the weaknesses of previous racial studies. Vast amounts of data now show population differences in blood-group frequency. As such antigen systems directly express the genotype, which more complex traits like skin colour or body height do not, it was once expected that a coherent genetic classification of the. Human populations might emerge. This has not been the case. The ABO blood groups were first described in 1900. They are strongly patterned over the surface of the world. Groups A and B are both at high frequency in Africa and much of Asia, extending into the Pacific through Melanesia. In northwestern Europe, B is lower, O and A higher. In native populations of the Americas, A and B are almost absent, except in western central North America, where A becomes common. In Polynesia, B declines towards the periphery and A and O rise, and in aboriginal Australia again, B is absent and A is high. Such a distribution is difficult to interpret in purely historical terms. Gene frequencies appear to be relatively stable over moderate amounts of time; for example, gypsies in Western Europe preserve frequencies close to those of their original home, India. The worldwide distribution might suggest the operation of selection, but little is known about such selection on the ABO system (although a history of differential resistance to disease has been suggested). The founder principle and genetic drift may be more important. For example, the settlement of Polynesia, beginning about 1500 BC, involved a serial colonization of island groups eastwards. Such a succession of small groups, probably composed of related families, each drawn as a minor part of the last, is the ideal situation for the reduction and loss of a gene by chance in small samples. Similar chance events may have applied in the small tribal populations of Australia, which probably suffered occasional extinction and repopulation during an occupation of the continent going back to about 500000 years. For the Americas, movement by immigrants from Asia across die relative cold of the Bering Strait area might have led to a purge of disease organisms, so that both chance and the removal of an agent of selection by disease caused the A and B alleles to decrease (Jones et al., 1992).

As natural selection eliminates history, the present distribution of the ABO gene frequencies is unlikely to retain much evidence of ancient migrations and population relationships. The same may be true of most other blood-group systems. The MNSs system is complex: the M allele is somewhat more frequent than N in Europe and Africa, M is very high in the Americas, and N very high in Australian aboriginals. The Rhesus (CDE) system is more complex still, with many variants. Again, the adaptive qualities of each in relation to disease are not known, and their distribution might reflect older disease patterns that have changed greatly in recent times. The MNSs and Rhesus systems have variants peculiar to or especially frequent in Africa, to a degree that might suggest a long isolation of these populations from those of Europe or Asia. Similarly, the Duffy system with two antigens a and b also has a ‘silent allele (Fy1), which is virtually restricted to Africa and gives some protection against the form of malaria caused by Plasmodium vivax. Plasmodium falciparum, which causes more taxing malaria, is resisted by haemoglobin S, the haemoglobin sickling variant. The Gm trait of blood serum consists of several antigens, which occur as sets-of linked loci, inherited as groups or haplotypes. It shows sharper differences among major populations than do most red-cell systems, and may hence be more informative about their past distributions. The antigens on white blood cells resemble the Gm system in that they are complex linked blocks of genes, and also promise an insight into the long-term association of such linkage groups with particular populations. All these systems are useful for micro evolutionary studies. Sometimes they even show some correspondence with local linguistic change.

For example, on the island of Bougainville in the Solomon’s, Melanesians speaking Papuan languages have MNS frequencies quite distinct from those of neighboring tribes speaking Austronesian languages (whose frequencies resemble those of Austronesian speakers elsewhere in the Solomons). However, the same distinctions do not hold for New Guinea. A further insight into patterns of relatedness emerges when blood systems are combined to give a compound measure of genetic distance. Europeans then appear to be closer to Africans, and Australoids to Mongoloids. However, most of the variation in blood groups is between individuals within populations and between small groups, not between the so-called ‘races’ of humankind. Such compound measures of affinity are particularly influenced by one or a few highly variable systems (such as Gm), so that newly discovered genes may not provide much new information (Jones et al., 1992).

Genetic study at the molecular level is so laborious that it has not yet given much new insight into the differences among human populations. One attempt has been made, using the gene cluster of human p-haemoglobin. Using restriction enzymes to find cleavage sites detects the presence or absence of these sites and produces a series of closely linked genetic differences or haplotypes. Study of individuals from different regions suggests that Africans form one grouping and all non-Africans (including Melanesians, Polynesians and Asians) form another. One application of molecular techniques may be particularly promising. This uses the DNA of the mitochondria, the sites of energy metabolism in the cytoplasm of cells. This extra-nuclear DNA (mtDNA) consists, in humans, of a loop of 16500 base pairs, far less than the total chromosomal DNA. It is hence much easier to analyze in detail, and the complete sequence of mtDNA is known. This DNA is transmitted only in the maternal line, via the ovum, and is not subject to the shuffling of gene groups – recombination – found in the nucleus. Change takes place only through mutation, which takes place at a much higher rate than in nuclear DNA. Studies of mtDNA determine maternal lineages. These may be very ancient. They differ by virtue of substitutions at various restriction sites. One study based on 12 restriction enzymes revealed 196 polymorphic sites, many of which can distinguish among a number of different female lineages. The largest number of different lineages occurs in Africa. By this hypothesis Africa seems to be the source of populations elsewhere in the world, with new lineages arising in the emergent population. Thus, other regions of the world have both ‘African’ and non-African lineages. Europe was colonized by populations having a large number of female lineages (albeit fewer than Africa, with Asia, Australia and New Guinea founded by successively smaller numbers of lineages. This pattern might arise because population bottlenecking has reduced the numbers of lineages. The assemblages of lineages in a particular place are not specially related, although one New Guinea cluster seems to have its closest relative in Asia, not Africa. In Asia, a deletion of a short section of the mtDNA is common to Chinese, Japanese and some Pacific peoples. It is also found in South America. Rates of lineage divergence are about 2 to 4 per cent per million years, using the probable times of human colonization for America and New Guinea as a reference point. If this clock is accurate, a common ancestor might then have existed in Africa at some time from 290000 to 140000 years ago. Humans may have migrated from Africa during this period, and because the oldest population cluster of types outside Africa with no African types is estimated to be 90000 to 180000 years old, this sets an approximate minimum age for the emergence of these people from Africa. mtDNA gives some fascinating hints about ancient migrations. However, in other animals, such as mice and fruit flies, patterns of distribution of mtDNA appear to give positively misleading clues about patterns of historical relatedness among populations. The mitochondrial case is as yet far from proven (Jones et al., 1992).

However, most molecular patterns do lean towards the hypothesis of dispersal of modern humans from one general area – Africa. They also imply that racial distribution is two-dimensional, with no important contributions to modern populations from ancient peoples, such as local survivors of Homo erectus. mtDNA mapping does seem to provide the possibility of long-range probes of the past. None of the lineages yet found is sufficiently divergent from others to suggest that it arose before the appearance of modem Homo sapiens.

The Peopling of Pacific

The patterns in genes in modern populations, confirm some of his views, and add a great deal to our understanding of this area, which includes some of the first and some of the last parts of the world to be occupied by modern humans. The archaeological and fossil records suggest that we got to some places very early on. Recent finds of stone tools and red ochre’s in Arnhem Land in northern Australia show that humans were there between 60000 and 50000 years ago. They reached Tasmania more than 20000 years ago, extinguishing many native plants and animals on their way. In Papua New Guinea, too, there has been human habitation for at least 40000 years. In contrast, many of the Pacific islands have been settled for less than 5000 years, and islands such Pitcairn were occupied 1000 years ago with populations that then became extinct. Language supports this pattern of settlement. In Papua New Guinea, an ancient homeland populated by groups isolated from each other by geography and culture, there are about 700 languages, “many of which are very distinct and have only a few speakers. In the highlands, there were ditches for drainage and for growing taro tubers at least 9000 years ago. The other main centre of languages – and of an expanding agricultural population -in the Far East was in the Yangtze (Chang Jiang) basin in eastern China about 8000 years ago. These rice growers spread southwards and were the source of a vast movement of people, cultures and genes that today covers much of eastern Asia and the Pacific. Their culture and the Austronesian languages associated with it spread to the Philippines by 3000 BC, to , central Polynesia by 200 BC and ultimately to Hawaii (AD 300) and New Zealand (AD 800). The vast area has a common linguistic heritage: the word for ‘eye’ (mata) is the same in the Philippines, Fiji, Samoa and Easter Island. Many genes- for blood groups, enzymes, mitochondrial DNA and nuclear DNA sequences have been mapped in the Pacific region. Some clear large-scale patterns emerge. There is a genetic link -as the eighteenth-century voyagers saw -between the modern populations of Southeast Asia and those of the myriad of small islands making up Polynesia. This is clearly seen in the patterns of the maternally inherited mitochondrial genome. In Japan and East Asia, many people lack a short section of the DNA in the mitochondrion. This deletion does no harm, but is a characteristic of Southeast Asian populations. It is also found throughout Polynesia, and on the coast of Papua New Guinea, bolstering the linguistic ties that show that these peoples originally came from somewhere in that part of Asia. However, the native populations of central New Guinea and of Australia, with their wild diversity of language, do not carry this ancestral cue; they travelled more slowly and for far smaller distances than did the Polynesians. Populations of the most distant Polynesian islands are genetically rather uniform, .suggesting – not surprisingly – that they went through a series of bottlenecks as they spread across the Pacific, in the isolated parts of Papua New Guinea, too, there is a shortage of genetic variation, showing that these mountain valleys are just as isolated (Jones et al., 1992).

Morphological Patterns of Relationship

Other information is also useful in studying historical relationships. Fingerprint and palm print patterns in Pacific populations show a striking separation: Polynesians, Micronesians (both speakers of Austronesian languages), Melanesian Austronesian speakers and other Melanesians further divided by the Papuan language spoken can all be distinguished. This may reflect a history of subdivision and drift in these island populations. This pattern is much clearer than that which emerges from blood-group studies in the Pacific. The dispersion of these populations may have started 4000 years ago or more. Fingerprint analyses have not yet been carried out on continental populations, but the method might be valuable for studying problems such as the history of migrations among American Indians.

Other useful morphological characters include those of the skeleton. Cranial measurement had its beginning in the first half of the nineteenth century. A large amount of information soon became available; as skulls could be collected while living individuals could not. The only analysis was to use ratios/indices to convey shape. The cranial index (breadth over length x 100) classed specimens as dolichocranial (long, with an index below 75), mesocranial and brachycranial (short, index over 80). Other ratios also proliferated: relative height of skull, height of face, breadth of nose, and so on. This approach was often used to produce a classification based on combinations of such categories. Populations of skulls were commonly subdivided into ‘types’, which were supposed to have entered into the population at its origin. In spite of the vast amounts of information gathered, it soon proved impossible to make effective comparisons or to produce population histories based on anything more than supposition. The Coefficient of Racial Likeness was an attempt by the English statistician Karl Pearson to compare skull series by combining a number of measurements. This was a first attempt to gather the information present into a whole and it gave impetus to the collecting of sets of skulls.

However, the method failed to take account of the correlation among measurements, and hence placed too much emphasis on difference in overall size (Jones et al., 1992).

Since Pearson’s time, this problem has been overcome by computers and the development of multivariate statistics. These summaries measurements as a new set of transformed figures between which correlation is removed and which are more specific in meaning and importance (‘Discriminant functions’ or principal components are usual forms). These help to relate populations to each other, and they also reveal a lot about the underlying differences in form. Such techniques tend to gather populations of skulls into groups corresponding quite well with geography – that is, Africans, Europeans, Australo-Melanesians, Far East Asiatics, Polynesians and American Indians. Discrimination among these is mainly based on distinctions not fully revealed by the traditional measurements or ratios. Breadth of the cranium, particularly at the base, is a major factor, as is relatively anterior or posterior positioning of the face, especially at the sides of the facial mask. Such distinctions are most marked between Inuit or inner Asiatic Mongoloids -such as Buriats of the Lake Baikal (Ozero Baykal) region on one hand, and Africans and Australo- Melanesians on the other (Jones et al., 1992).

Fine distinctions in the relative projection of the root of the nose and the eye orbit are also important. Mongoloids such as the Buriats have a relatively high face. Inuit of Greenland have very flat faces, with a flat nasal saddle. Polynesians, as exemplified by Hawaiians, have large and quite flat faces; they are distinguished by a particularly prominent upper nasal and facial region. American Indians and Europeans are not far from the global mean in any direction, although the Americans are somewhat closer to Hawaiians than to Europeans. American Indians have a flatfish face, but the root of the nose and the space between the eyes is relatively high. Australians and Melanesians have narrow skulls and low faces, with a jutting tooth-bearing part, which, together with a protruding eyebrow ridge, dis-tinguishes them well from Africans The African face is short but broadish across the eyes, and the skull is narrow. Though small-skulled, southern African San (Bushmen) share the main African characters. Such cranial analyses can also be used on prehistoric material. An analysis of ‘size’ and ‘shape’ distances based on the means of nine measurements on a large number of European skull series from the Mesolithic to Roman times shows a general homogeneity among groups from any given cultural complex, such as the Bell Beaker people in the third millennium BC. It also discerns two major cranial forms- long-skulled/broad-faced in the north and long- skulled/narrow-faced in the south. The latter form (sometimes referred to as Mediterranean) appears to have expanded at the expense of the former (the Cromagnoid). These real differences in skull form do not coincide at all with the long-accepted typological ‘races’ in Europe – Nordic, Mediterranean and Alpine. Indeed, the last, traditionally seen as an invading physical group, disappears (Jones, et al, 1992).

Such multivariate comparisons might also be used to study much older specimens. Late Pleistocene skulls do in some cases approximate to their regional successors; examples are Mladec 1 (for Europeans) and Keilor (for Australians). There are, however, difficulties in applying these techniques, which are only partly due to insufficient material. One is statistical. Another arises from the fact that there are slightly greater differences between ancient and modem peoples than appears to the eye. For example, specimens from Liujiang in southern China or Border Cave in South Africa have a prominent eyebrow ridge in an otherwise modem-appearing skull. Modem humans appeared indifferent parts of the world at widely differing times. In Africa and Southwest Asia, they were early. They may have been excluded from Europe, constrained by the presence of Neanderthals, as they appeared there only about 38000 years ago when they had already reached Australia and a few Melanesian islands. The Far East is difficult to assess. The Liujiang skull, however, is believed to have a date of 67000 years. The remains from: Zhoukoudian (Upper Cave) are 20000 to 30000 years old (Jones, et al, 1992). Although modem, their shape suggests that they are not antecedent to today’s Chinese, and their affiliation is not clear.

The New World does not help us with the emergence of modem populations generally, because the first American arrived so recently. There is considerable variation in physical and cranial form among the indigenous American populations, which might result from differences among arriving migrant groups. It might also arise from local micro-evolution and the founder effect. On the other hand, son features are shared by all New World populations, whir distinguishes them within the general Mongoloid group.

There are two views of the arrival of the first American One, involving linguistic and genetic evidence, envisage three main migrations: Paleoindian (the earliest and the one responsible for most of the variation); Na-Dene (now centered on northwestern North America); and Eskimo-Eleut. The migrating populations are supposed to have originated in three areas of northeastern Asia: the north coasts the interior and the Pacific littoral, respectively. The second hypothesis proposes a first movement, at perhaps 20000 years ago, which penetrated south via a corridor between the existing ice sheets, and a second that was held up until the icecaps melted and which gave rise to northern tribes and Inuit. A problem in all this is the poverty of archaeological evidence before about 120000 years ago. A few cave sites in North and South America, such as Pedra Furada in Brazil, are believed by some workers to give such evidence. But not all are persuaded; in spite of much research, there are no signs of widespread occupation of the Americas during the late Pleistocene, or of coherent cultural patterns like those evident in Europe and Australia. Australasia is another matter. Although there were considerable expanses of water along the migration route, people were occupying Australia and New Guinea (then joined by a land bridge) at least 50000 years ago. Aboriginal populations of recent times show little variation: North Australians are perhaps closer to Melanesians than are others, and the Tasmanians (now extinct) also differed slightly from other Australian populations. There was greater variation at many times before 6000 years ago, to the extent that the specimens are often divided into ‘robust’ and ‘gracile’ groups. To the former belong the more heavily built skulls from Kow Swamp, Lake Nitchie and Willandra Lakes. In the latter group are the less-robust specimens from LAKE Mungo and Keilor. Migrations from different regions have been postulated to explain these differences, as has input from a south-east Asian Home erectus population (Jones et al., 1992).

Conclusion

However the morphological diversity within early Australians was merely, variation on only one fundamentally similar form as Melanesian and Australian populations form a broad grouping which Craniometry distinguishes from those of other Asian regions. Any attempt at an analysis of long-term population movements needs a starting-point, or root. This is not only hard to define but also presupposes the existence of one original population, and migration outwards from this single source. Evolutionary trees, however extensive the information on which they are based, are hence not in themselves able to distinguish between the two hypotheses for modern origins. However, some findings do emerge from such comparisons. Although not many specimens are available, skulls that can readily be related to fully modem specimens do not extend far into the past; perhaps around 30000 years. By contrast, existing populations are surprisingly close to one another. Neanderthal and other archaic specimens are certainly far removed from modem populations. These results appear to negate the explanation of regional continuity and evolutionary divergence. However, they are neutral in the matter of African origins for Homo sapiens. Although the earliest skeletal remains (Lake Mungo) are about 30000 years old. The continuous archaeological record in Australia may go back at least as far as 50000 years ago (Jones et al., 1992).As there was probably only one general avenue of entry to the continent and as there are no signs (in spite of the robusticity of such specimens as Kow Swamp) of evolution from Homo erectus within it. Australia probably contains the earliest evidence of fully modern humanity outside Africa and the Near East. The implications of this for the theory of the spread of modem humans from Africa to the east remain uncertain.

Summary

The biological variety of living human populations since the beginning of anthropology have been approached through the study of race. For almost two centuries following Linnaeus, anthropologists attempted to define discrete units of humanity, and to find criteria for distinguishing among these ‘races’ as sharply as possible. Individual’s best conforming to such criteria were viewed as ‘pure’. All this happened before the emergence of genetics. Human populations in different parts of the world have adjusted to the physical environment in various ways, but surprisingly little is known of the adaptive significance of these physical differences. The worldwide distribution might suggest the operation of selection, but little is known about such selection on the ABO system (although a history of differential resistance to disease has been suggested). The founder principle and genetic drift may be more important. Other useful morphological characters include those of the skeleton. Cranial measurement had its beginning in the first half of the nineteenth century. A large amount of infor-mation soon became available; as skulls could be collected while living individuals could not. The only analysis was to use ratios/indices to convey shape. The implications of this theory of the spread of modem humans from Africa to the east still remains uncertain.

References

• Cook, J., & Ward, C. (2008). Conservation assessment of the Neanderthal human remains from Krapina, Croatia and its implications for the debate on the display and loan of human fossils. British Museum technical research bulletin, 2, 39-44.
• White, T. D., Black, M. T., & Folkens, P. A. (2011). Human osteology. Academic press.
• Alfonso, M. P., & Powell, J. (2007). Ethics of flesh and bone, or ethics in the practice of paleopathology, osteology, and bioarchaeology. Human remains: Guide for museums and academic institutions, 5-20.
• HILLS, C. (1992). The Cambridge encyclopedia of human evolution. Cambridge: Cambridge University Press.
• Fenton, C. L., Rich, P. V., Fenton, M. A., & Rich, T. H. (1989). The fossil book: a record of prehistoric life. Courier Corporation.
• Seilacher, A. (2007). Trace fossil analysis. Springer Science & Business Media.
• Tattersall, I. (1995). The fossil trail: How we know what we think we know about human evolution.
• Oxford University Press, USA.
• Etler, D. A. (1996). The fossil evidence for human evolution in Asia. Annual Review of Anthropology, 25(1), 275-301.
• www.mhhe.com/biosci/genbio/raven6b/graphics/raven06b/other/raven06b_23.pdf http://humanorigins.si.edu/evidence/human-fossils/fossils/cro-magnon http://www.shareyouressays.com