Genetics In Anthropology Research Paper

1. Human Variation

When laboratory techniques for studying Mendelian traits first became available, international anthropology had just emerged from a serious controversy over racial typology during which Franz Boas, recognized by many as the founding father of American anthropology, had repudiated to the satisfaction of most anthropologists the racial theories of Gobineau and his intellectual heirs. Originally trained as a physicist, Boas presented data and arguments between 1910 and 1913 showing that ‘race,’ ‘language,’ and ‘culture’ were three independent phenomena which, he asserted, should all be studied by anthropologists, but using different kinds of theories and techniques. On the heels of this observation, the Hirzfelds, building on the work of Landsteiner and others, showed in 1919 that while the ABO blood system was universal among human populations, the phenotypes and hence the alleles, the alternative forms of a gene, were in different proportions, thereby supporting Boas’ contention that the differences among ‘racial’ populations were not qualitative but quantitative (Weiss 1998). The ability to taste PTC (phenylthiocarbamide), a simple Mendelian trait, also seemed to occur in many different human populations, likewise in different frequencies. But other apparently Mendelian traits examined early in the century—eye color, skin color, and ear lobe shape—turned out to embody genetic relationships with a much more complex genetic architecture (McKusick’s current list of over 30,000 Mendelian traits can be found at World Wide Web URL: http://www3.ncbi.nlm.nih.gov/Omim/).

Data on human phenotypes assembled for military purposes in World War I continued to encourage anthropological geneticists in the decades following the war. In addition to complex and composite anthropometric traits such as height and weight, the military was especially interested in those factors that affected the compatibility of blood and blood components used in transfusion. The collection of such data was continued through World War II, when most European and American soldiers and sailors were typed for ABO and Rh factors during initial processing, and this body of data became generally available to scientists after 1945 (Harrison et al. 1964).

For anthropologists, the major theoretical model which emerged to describe human genetic variation in this period was the notion of cline, the gradual geographic change in the frequency of an allele, which also served to undermine further the idea of racial typology. As regularities began to emerge, especially in the European data, it was found that the alleles of a gene, and also phenotypic traits such as red hair, seemed to vary across the landscape in a regular manner. These were mapped using arrows to show the direction of increasing frequency of one of the component alleles of a gene, or by isographs which identified geographical areas where allele frequencies were within a particular range. Traits mapped in this manner included blood system alleles, phenotypic traits, and also diseases which were suspected of having a simple genetic basis, such as albinism, color blindness, and some types of cancer (Harrison et al. 1964, pp. 234–76).

Some patterns which emerged from the analysis of clines conformed to more general biological principles pertaining to other animals. It was found, for example, that Gloger’s, Bergmann’s and Allen’s Rules for variation within a mammalian species (pertaining to pigmentation, mass, and limb length, respectively) were also valid for the human species, reflecting adaptation to the different latitudes, climates, and environments inhabited by local human populations. Since these traits were so clearly adaptive, it was suspected that other patterned traits, with definite clines, likewise reflected genetic adaptation to local conditions.

2. Adaptation

The most forceful new example of human genetic adaptation was presented by Livingstone in 1958 with his study of sickle cell disease, especially as it existed in Africa. In addition to presenting convincing evidence of several types to prove that sickled blood cells were a response to the presence of malaria, Livingstone’s work illustrated several other lessons in anthropological genetics. First of all, it was the heterozygote of hemoglobin S (HbS) which had the adaptive advantage, not the HbS homozygote, who often sickened and died. The second lesson was that an apparent ‘disease,’ sickle cell anemia, was on closer inspection actually a successful adaptive mechanism, a proposition which is still better understood by anthropologists and population geneticists than by their colleagues in clinical medicine (Weiss 1993).

Another highly visible connection between genetic variability, culture, and environment concerns the ability of human adults to digest milk and milk products from dairy animals, an ability that seems to be under genetic control. When mapped geographically, the alleles responsible for adult lactose tolerance in human populations seem to be correlated, in the Old World, with the locations of pastoral peoples. Significantly, populations where lactose tolerance is high include pastoral societies all the way from Scandinavia to southern Africa, producing east–west clines which cut across the north–south clines describing the distributions of all sorts of other phenotypical characteristics, including those related to latitude and climate (Durham 1991).

There are indications that the frequencies of many other diseases, such as cancer and diabetes, correlate with blood types and also with alleles involved in the digestion of food. People of A phenotype, for example (in the ABO system), may carry an increased risk of death from cancers of the esophagus, pancreas, and the stomach, but whether these diseases are in any sense ‘caused’ by type A blood, as the sickling trait can cause anemia, or whether both disease and blood type are derived from an independently variable genetic or environmental condition, is very problematic to clarify. Northern Scandinavia, for example, has a high frequency of type A individuals and a high incidence of stomach cancer. But their diet is different from other Europeans, and their climatic environment is different as well, so it is difficult to separate the variables which might cause stomach cancer (Molnar 1998, pp. 100–7).

Perhaps the most useful way of looking at the various genetic and environmental factors correlating with disease frequencies is to say that each ‘contributes’ to the likelihood that an individual will exhibit the disease (Terwilliger and Goring 2000). Many anthropologists argue that from the standpoint of adaptation, no gene of itself is a ‘bad’ gene. Like HbS, any allele manifested in the phenotype might be beneficial in certain circumstances. Among anthropologists, it is increasingly recognized that the relationship of gene to environment, like the relation of gene to gene, is very complex. Also, the distinction between ‘genetic disease’ and ‘infectious disease’ begins to break down when we consider that smallpox, for example, takes a more virulent course in people of blood type A or AB , as opposed to O or B (Stein and Rowe 2000, pp. 427–30).

The study of adaptation to cold climate and high altitude has provided an opportunity to differentiate between the effects of genetic differences among human populations and phenotypical differences engendered by growth and development—more simply, the difference between nature and nurture. Most recently, Beall has shown that Tibetan and Peruvian populations have a different genetic basis for their respective adaptations to thin air (hypoxia), but many other aspects of human adaptation to climatic extremes remain to be examined (Jones et al. 1992, pp. 46–51). These studies require the comparison of highland to lowland Peruvian Indians, and the examination of such characteristics as body type, especially lung capacity, and oxygen saturation rates among migrants and colonists in both locations.

3. Population Genetics

With increased funding for science in the United States after World War II, and increased access to field sites, anthropologists began to investigate isolated, small-scale human populations with renewed vigor, often including a biological anthropologist in the research team. The most visible of these joint enterprises was probably the comprehensive study of the Yanomamo, who live in the upper drainage of the Orinoco River in Venezuela and Brazil. In the 1960s, James Neel of the University of Michigan organized a comprehensive multidisciplinary series of field expeditions which investigated the environment, ecology, biology, culture, and social organization of these then little-known people. After a series of books and articles was published over the next two decades, the Yanomamo became not the least known but one of the best known tribal societies in the world.

For the genetics part of the research, Neel and Ward examined six blood systems relatively well known at the time (MNS, Rh, Kidd, Duffy, Diego, and haptoglobin) among seven villages of Yanomamo, seven villages of nearby Makiritare, and 12 other tribes of Central and South America (Neel and Ward 1970). After comparing the different groups, the authors concluded that human evolution might have been proceeding at a pace ‘100 times more rapid’ than previously thought, if these small-scale societies could be taken as analogues of earlier Pleistocene or Paleolithic human peoples.

In the same period, Friedlaender and Harpending were proceeding with similar investigations in Oceania and Africa, respectively. Working in the Solomon Islands from 1966 to 1973, sometimes alone and sometimes as part of a multidisciplinary team, Friedlaender simultaneously undertook studies of demography, anthropometry, genetics, and social structure, seeking to integrate his results into some general conclusions that cut across these traditional fields of research. Like Neel and Ward, he emphasized the genetics of blood systems, in this case ABO, MNS, Rh, Kell, and Duffy. In these years, blood system alleles were not sequenced directly, but determined from immunological reactions to blood proteins, usually through the intermediary use of rabbit antibodies (Jones et al. 1992, p. 304). From this kind of data, Friedlaender calculated phenotype frequency and then allele frequency by techniques described in his major ethnographic work, Patterns of Human Variation (Friedlaender 1975). His most general conclusion, combining results from anthropometry, dermatoglyphics, genetics, and demography, was simply that Bougainville communities tended to exhibit high biological variability within the group, but low variability among the groups, and that some traits, such as skin color, eye color, and hair form, were ‘monotonous’ on the island, while dermatoglyphic characteristics and some blood system alleles were discontinuous from village to village.

Those expecting that these early studies would provide fundamental insights into the mechanisms of human evolution were soon disappointed. Summarizing a widely shared consensus of opinion in 1974, Harpending concluded (1974, p. 229):

… studies of the genetic structure of small populations have made particular and incidental contributions to formal genetics, to regional history and prehistory, to epidemiology, and to several other fields to which they are peripheral, but … they have not advanced our understanding of human evolution in a global sense. The sample sizes available have been too small to allow reliable inferences about natural selection; the extensive occurrence of what is presumably local random genetic drift has little or no consequence for evolution over long time periods over large areas; and the presumed selective agents in the various environments of these peoples differ greatly so that few of the generalizations which have been put forward hold for many groups.

4. Evolution Of Primates

Although anthropologists, even before the publication of Darwin’s Descent of Man had recognized that humans and apes were closely related, the significance of the differences between them had been both exaggerated and misunderstood. Based on the fossil record, the split of humans from the ape line had been put far back in time, about nine million years, and it was assumed that all the ape species were closely related to each other and quite distinct from humans. Therefore the allegation of Sarich and Wilson, published in 1967 and based primarily on immunological data, that humans and apes had diverged as recently as five million years ago (mya), created a serious confrontation between ‘the bone people’ (paleontologists) and ‘ the lab people,’ human geneticists such as Sarich and Wilson. The former accused the latter of inaccuracies in their assumptions about the speed of ‘evolution,’ in this case the evolution of blood albumin, while the latter accused the former of manipulating primate taxa to preserve the supposed profound differences between ape and human. In fact the fossil Ramapithecus, with an antiquity of about 14 mya, soon fell out of the human lineage on osteological grounds, so that even the fossil evidence seemed to point to a more recent divergence between human and apes.

Beginning in the 1970s, Morris Goodman and his associates have become prominent in the reconciliation of fossil and biological evidence which, taken together, provide the best description of the evolution of apes and humans. In 1974 Goodman proposed that humans, chimpanzees, and gorillas should join humans as hominines, a subfamily of the family Hominidae, perhaps leaving the more distantly related gibbons and/orangutans as separate families or sub families. Goodman’s conclusions, like those of Sarich and Wilson, were based on molecular data, in this case amino acid sequces from blood proteins.

Goodman’s current synthesis (1999) includes data from many kinds of direct sequencing of DNA from humans and other primates, especially the β-globin gene cluster, and from the analysis of morphological features, especially certain diagnostic skeletal features on living and fossil primates. His current picture of relationships among living humans and apes shows a split between the Tribe Hominini and the lesser apes about 18 mya, between orangutans and the Subtribe Hominina about 14 mya, and among gorillas, humans, and chimpanzees within the last seven million years. The timing and significance of the chimpanzee– bonobo separation has not yet been firmly established, since they have only recently been recognized as distinct species, and basic comparative genetic studies of both groups are now underway.

5. Methods

Although thousands of laboratory procedures have been developed over the last half-century, especially by medical researchers, to elucidate the structure of the human genome and show how it reproduces itself, certain techniques and certain targets have been more interesting to anthropologists because of their particular research agenda. Ideally, anthropologists interested in adaptation would like to know the locations of all human genes on the chromosomes, the number of alleles for each gene, and the locations of all loci involved in constructing a protein, but in practice researchers have had to settle for much less. Early in the twentieth century, the identity of alleles had to be teased out of complex immunological procedures in the laboratory. Later, proteins could be examined directly, but without much knowledge of the DNA structures, the precise sequence of nucleotides which had produced the protein. But with the development of slow though reliable DNA sequencing procedures in the 1970s, anthropologists became much more selective about which portions of the chromosomes they wanted to study, and for what purposes.

Surprisingly, with the inception of direct sequencing, it was discovered that perhaps 93–97 percent of the mass and length of human chromosomes consisted of apparently inactive regions variously called introns, satellites, tandem repeats, noncoding regions, or even ‘junk.’ Almost immediately these regions began to attract the attention of anthropologists even though they did not contain genes. It was the presumed inactivity of these regions which was interesting, since accumulated mutations on these regions were apparently selectively neutral, that is neither favored nor disfavored by natural selection. Therefore, it was reasoned, they might in a more accurate, clock-like manner reflect not only the relationships among primate species, but also the migrations and gene flow of ancient human populations. That is, satellite DNA was considered to constitute a ‘passive’ record of evolutionary events, rather than comprising active agents under selective pressure.

5.1 Stains

As soon as chromosomes could be observed directly through microscopes, attempts were made to stain them chemically so that bands would appear which might show differences in structure. Initially, the purpose was to discriminate among the different chromosomes of the human karyotype, or suite of chromosomes (22 autosomes, 1 X and 1 Y), so they could be counted and numbered. During the course of this research, it also became apparent that patterns of stains on a particular chromosome might vary from one individual to another within a population. In addition, when it was noted that certain patterns of staining were characteristic of particular species, yet another method became available for evaluating the phylogenetic relationships among apes and humans. At first the functional significance of the patterns was unknown, but this is changing rapidly as new techniques allow the identification of gene-rich regions identified by stains.

5.2 Restriction Enzymes

In 1973 it was discovered that certain enzymes, mostly recovered from bacteria, could sever a strand of DNA selectively at locations defined by a known base pair sequence. For example, the enzyme AluI recognizes the sequence AGCT and cleaves DNA at that location to produce fragments which are on average 300 base pairs in length in humans. The resulting distribution of segments of different length serves to define the structure of a chromosome, even without knowing the entire succession of base pair sequences on each segment. An appropriate enzyme, or several enzymes applied in series, can be selected to produce a small or a large number of segments, long or short, depending on the purposes of the research. By comparing the phenotypes of individuals contributing DNA samples and examining their pedigrees, ‘linkages’ could then be discovered between particular alleles included in the same segment.

Electrophoresis, which had previously been used to separate blood proteins obtained from serum, can be used to separate DNA segments according to size and net electric charge, with the segments sometimes enhanced or differentiated visually by using a large number of new stains developed in the last two decades of the twentieth century, some of which are fluorescent. In the 1980s, the PCR (polymerase chain reaction) ‘revolution’ occurred, which allowed researchers to clone or amplify small pieces of DNA indefinitely. PCR procedures make it possible to amplify a tiny bit of DNA clipped from an electrophoresis gel, or even a single sequence from a single cell, to obtain sufficient material for analysis (Hillis et al. 1996). All of these became useful tools for describing genetic variation in a population within a species, or to compare and contrast variations between and among species.

5.3 Chromosome Mapping

A major objective of human genetics research is to locate all genes on their respective chromosomes as well as to identify all the other functional regions of DNA, including some formerly dismissed as ‘junk.’ One technique for gene mapping involves the use of genetic markers, like the restriction enzyme sites described earlier, or other DNA sequence variants discovered by various means at hundreds of other chromosome locations. Because many of these are relevant to human disease, high levels of funding were made available to the Human Genome Project to identify the location of these variable sequences or ‘polymorphisms.’ This support has led to the development of very fast computer and molecular technology and machinery, and much of the resultant data appears in easily searched form on the worldwide web.

5.4 Mitochondrial DNA (mtDNA)

Most human genes reside in the nucleus of the cell and occur in two copies, one each inherited from the mother and the father. However, the body or cytoplasm of each cell also contains structures known as mitochondria, which are involved in the production of energy for the cell and contain their own DNA. This DNA is special in many ways. At fertilization, the mitochondria of the ovum are transmitted to the offspring, but the mitochondria of the sperm are not. Thus mtDNA is inherited in a strictly maternal manner, a biological phenomenon which parallels several important sociological phenomena of special interest to anthropologists, such as matrilineal clan membership.

Since mtDNA is haploid rather than diploid in form (a single rather than double strand), it does not recombine during replication, and over time, as sequence variations accumulate through mutation, it produces distinct, diverging, lineages of mtDNA sequences. This variation can be used to reconstruct the mtDNA structure of the common, apical ancestor (the coalescent sequence) from a sample of mtDNAs collected from individuals alive today. Because the mitochondria are so numerous in the cell, mtDNA can be recovered much more easily than DNA from the nucleus.

The mtDNA chromosome takes the form of a relatively small ring of 16,500 base pairs (16.5 kB), which was entirely sequenced by 1981. By 1987, 147 human individuals had contributed additional sequences and the structure of the converged mtDNA lineage was announced, which ‘coalesced’ on a woman who was promptly dubbed ‘mitochondrial Eve,’ alleged to have lived in Africa about 200,000 years ago, and whose ‘modern human’ progeny had emigrated from Africa and repopulated the world, which was at that time allegedly occupied entirely by earlier forms of human, such as Neanderthals and Homo erectus (Cann et al. 1987).

5.5 Y Chromosomes

There is one DNA molecule that is uniquely inherited in the paternal line, a kind of mirror image of mtDNA. When it was discovered that certain regions of the Y chromosome were very stable and apparently did not recombine during meiosis, it was hoped that the Y chromosome would become the analytic reciprocal of mtDNA. That is, Y chromosome lineages should parallel patrilineal social practices in the same way that mtDNA lineages paralleled matrilineal social practices. A dramatic confirmation of the utility of Y chromosome analysis has been provided by Thomas et al. (1998) who showed how Y chromosome lineages confirmed the patrilineal inheritance of the Jewish priesthood among widely dispersed Jewish populations. Seielstad and others have opened another promising line of research by comparing the geographical distributions of mtDNA and Y chromosome lineages in attempts to reconstruct the marriage practices of prehistoric peoples (see Y-chromosomes and Evolution; Stoneking 1998).

5.6 Satellites

Although the picture is constantly changing, researchers at this point recognize three general categories of tandemly repeated sequences, which are classified by length. They are satellites, the longest sequences, minisatellites, defined as sequences which are 500–40,000 base pairs in length, usually consisting of five or fewer repeated nucleotides, and microsatellites, which tend to be short and simple in motif, even consisting of repeats of a single base pair, or a triad or tetrad of nucleotides (for example, CACACA or CAGCAG) (Jackson et al. 1996, pp. 171–210).

These short, apparently neutral sequences are useful to anthropologists because their rate of mutational change is much higher than the single nucleotide mutation of DNA, so that minisatellites and microsatellites, like mtDNA, provide a finer control of historical relationships among individuals and the populations they represent. While the mutation rate for single nucleotides is about 10^-7, the rate for microsatellites is about 10^-3per generation.

6. Grand Synthesis

Before the entry of genetics into anthropology, the recent history of our species, over the last 6,000 years, was determined largely from written accounts or, in the case of preliterate societies, from oral narratives. To reconstruct events farther back, in the late prehistoric period, archaeologists examined architecture and technology, with architecture becoming less important farther back in time and technology, especially stone tools, becoming more important, especially before the Neolithic period began about 10,000 years ago. In all periods, compared to cultural remains, biological evidence in the form of graves and fossil humans has been rare, and the interpretations have been controversial.

In some ways, the present evolutionary debate among anthropological geneticists can be seen as a continuation of an historic dispute in paleontology between ‘lumpers’ and ‘splitters.’ Lumpers have historically emphasized the general evolution of the whole species, while splitters have tended to group human fossils into named regional and temporal categories, which were considered to evolve somewhat separately and independent of other regional populations. Splitters tended to assign new names to new fossil finds, while lumpers were reluctant to inaugurate new taxa, emphasizing instead the ongoing wide diversity within the human species.

The nature of genetic evidence lends itself to the continuation of this kind of debate. To a considerable extent, all modern human populations share similar alleles, and can be distinguished in this respect only by their different frequencies. An array of allele frequencies from a population can in principle be analyzed as a combination of two or more previous arrays, identified by name and allegedly specific to some region. This is a splitter’s approach. On the other hand, genetic ‘lumpers’ can maintain that the human species has always been diverse, and is no more heterogeneous now than it was hundreds of thousands of years ago.

The debate can also be characterized as between cladistic theorists who see local or regional human populations as largely maintaining their social and biological integrity, increasing in size, dividing into daughter groups, and then migrating to replace less successful populations. By contrast, ethnogenetic theorists postulate that gene flow by reciprocal marriages or matings among small adjacent populations might be as significant as long distance migration in changing regional allele frequencies, and that while language and culture might change rapidly within a region, biological characteristics change more slowly.

Luca Cavalli-Sforza and his colleagues have been prominent in this debate, and viewed by many as leaders of the cladistic school of thought. In the final decades of the twentieth century, they have produced several important theoretical books, followed by a huge compendium of maps, tables, and texts showing known global genetic variation (Cavalli-Sforza et al. 1994). In this school of thought, current human genetic variation is explained as the result of historic and prehistoric migrations of named ethnic groups from region to region and continent to continent, especially including the ‘African Replacement’ by Eve and her progeny.

If these works have not entirely convinced all of their academic readers, they at least have served as a convenient target for ‘lumpers’ and advocates of ethnogenetic theory. Prominent among these critics has been Milford Wolpoff, who argues, primarily on the basis of osteological evidence, that global human evolution has been mostly in situ, since modern populations, in the Far East for example, tend to reflect unique or unusual osteological features exhibited by pre-Eve residents of the region. The other main line of criticism has been from linguists and social anthropologists, who argue that Cavalli-Sforza and his co-workers have got the languages and ethnography wrong, and that their hypothesized migrations and other social and linguistic processes cannot be confirmed independently (MacEachern 2000, Terrell 2000). Such critics argue that human groups, especially the small-scale hunting-collecting societies which existed in Paleolithic times, were more fluid and less bounded than required by the migration hypotheses.

Accumulating genetic evidence seems to support the migration hypotheses. Concerning Eve, other genetic lineages besides mtDNA also seem to coalesce at about 120–200,000 years ago, supporting the Out of Africa hypothesis. However, rates of evolution of sequences on the autosomal chromosomes are difficult to judge, and the particular histories of gene families and other segments of chromosomes, especially their evolutionary odysseys of travel among the chromosomes over the last millions of years, are just beginning to unfold.

The analysis of ancient DNA from human fossils has the potential for resolving many problems of human prehistory and evolution, provided that appropriate and usable DNA can be retrieved from scarce and damaged human bones, of great antiquity. Already the examination of mtDNA sequences from a few Neanderthal specimens has shown deep rather than shallow genealogical relationships to modern human sequences, as if indicating that modern Europeans replaced them, rather than being descended from them. A human of lesser age, the so-called and well publicized Tyrolean Ice Man, has an estimated antiquity of about 5,000 years, according to carbon-14 dating, and could have been ancestral to modern Central Europeans (Herrmann and Hummel 1994, Kolman and Tuross 2000).

The most formidable but most satisfying task facing anthropological geneticists in the near future is to continue the confirmation and criticism of the fit, or lack thereof, among genetic, linguistic, and archaeological evidence for human migrations. No technique has yet been found for differentiating allele distributions resulting from gene flow from those resulting from a sudden migration after several generations have passed. Intermarriage and recombination tends to blur the distinction, so that anthropologists for the next several decades will no doubt continue to debate the accumulating evidence for global, continental, and regional migration and gene flow.

7. Problems

The greatest barrier to using variation in DNA sequences—polymorphisms—to trace the antiquity of relationships among human individuals and populations is the unreliability of the molecular clock. While mtDNA sequences, DNA lineages constituting gene families, and specific microsatellite sequences can be arranged into evolutionary trees, no one knows for sure the time between each generation or branch of the tree. It is clear that the frequencies of base pair deletions and other forms of mutation are not the same in different chromosomal regions, and similarly the amount and dynamics of variation seem to vary greatly among regions on the same chromosome, and among the autosomes, the Y chromosome, and mtDNA. There also seem to be ‘hot spots’ where mutations or recombinations are more frequent, near telomeres and centromeres, for example. An additional concern in calibrating the molecular clock is that the ‘proofreading,’ repair, and editing functions of genetic reproduction seem to be uneven for different genes and loci (especially, mtDNA seems to have weaker repair systems), so that some sequences are actually much older than they appear, because they have been systematically repaired (Kumar and Hedges 1998). What all of this means is that each gene has its own history, and only by aggregating information from many such histories do some aspects of the picture of human history begin to emerge.

Bibliography:

1. Cann R L, Stoneking M, Wilson A C 1987 Mitochondrial DNA and human evolution. Nature 325: 31–6
2. Cavalli-Sforza L L, Menozzi P, Piazza A 1994 The History and Geography of Human Genes. Princeton University Press, Princeton NJ
3. Crawford M 2000 Anthropological genetics in the 21st century: Introduction. Human Biology 72(1): 3
4. Durham W H 1991 Coevolution. Stanford University Press, Stanford, CA
5. Friedlaender J S 1975 Patterns of Human Variation: The Demography, Genetics, and Phenetics of Bougainville Islanders. Harvard University Press, Cambridge, MA
6. Goodman M 1999 Molecular evolution ’99: The genomic record of humankind’s evolutionary roots. American Journal of Human Genetics 64: 31–9
7. Harpending H 1974 Genetic structure of small populations. Annual Review of Anthropology 3: 229–43
8. Harrison G A, Weiner J S, Tanner J M, Barnicot N A 1964 Human Biology. Oxford University Press, Oxford, UK
9. Herrmann B, Hummel S 1994 Ancient DNA. Springer, New York
10. Hillis D M, Moritz C, Mable B K 1996 Molecular Systematics. Sinauer Associates, Sunderland, MA
11. Jackson M S, Strachan T, Dover G (eds.) 1996 Human Genome Evolution. BIOS, Oxford, UK
12. Jones S, Martin R, Pilbeam D 1992 The Cambridge Encyclopedia of Human Evolution. Cambridge University Press, Cambridge, UK
13. Jorde L B, Bamshad M, Rogers A R 1998 Using mitochondrial and nuclear DNA markers to reconstruct human evolution. BioEssays 20: 126–36
14. Kolman C J, Tuross N 2000 Ancient DNA analysis of human populations. American Journal of Physical Anthropology 111: 5–11
15. Kumar S, Hedges S B 1998 A molecular timescale for vertebrate evolution. Nature 392: 917–20
16. Long J C 1993 Human molecular phylogenetics. Annual Review of Anthropology 22: 251–72
17. MacEachern S 2000 Genes, tribes, and African history. Current Anthropology 41(3): 357–84
18. Molnar S 1998 Human Variation. Prentice–Hall, Saddle River, NJ
19. Neel J V, Ward R H 1970 Village and tribal genetic distances among American Indians, and the possible implications for human evolution. Proceedings of the National Academy of Sciences 65(2): 323–30
20. Sarich V M, Wilson A C 1967 Immunological time scale for Hominid evolution. Science 158: 1200–3
21. Stein P L, Rowe B M 2000 Physical Anthropology. McGrawHill, New York
22. Stoneking M 1998 Women on the move. Nature Genetics 20: 219–20
23. Terrell J E (ed.) 2000 Archaeology, Language, and History. Bergin and Garvey, Westport, CT
24. Terwilliger J D, Goring H H 2000 Gene mapping in the 20th and 21st centuries: Statistical methods, data analysis, and experimental design. Human Biology 72(1): 63–132
25. Thomas M G, Skorecki K, Ben-Ami H, Parfitt T, Biadman N, Goldstein D 1998 Origins of Old Testament priests. Nature 394: 138–9
26. Weiss K M 1993 Genetic Variation and Human Disease. Cambridge University Press, Cambridge, UK
27. Weiss K M 1998 Coming to terms with human variation. Annual Review of Anthropology 27: 273–300