All life forms with DNA in their cells (or cell!) are related. Even you, dear reader, are related (and not all that distantly as the following figure shows) to any DNA-carrying animal, ciliate, plant or fungi you care to mention.
X you are here
34. What Does "Related" Mean?
by George Weber
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Table of Contents
1. Introduction 2. Relationships at the top level of the tree of life 4. Palaeoclimate and human ancestry 5. Speciation (the development of new species) 6. Modern human races (their skin colour, body size, etc.) 7. "Skull Measurers" and "Lookers" 8. DNA analysis (nuclear and mitochondrial DNA) 9. So, what does "Related" mean then? 10. Negrito relatives Far and Wide 11. Respect Them! |
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CAUTION: Readers who cannot accept Homo sapiens' evolutionary lineage and scientific classification within the Kingdom Animalia are entitled to their opinions but read this chapter at their own risk. Those who might have a problem with the term "Negrito" should first see FAQ ("Is 'Negrito' an acceptable term?"). |
1. Introduction
In any group dedicated to a specific subject, the danger of fixation on that one subject is ever-present. As for ourselves, we must beware of seeing Negritos under every bed. The danger is particularly acute in this and in the following chapters where we try to identify populations that might be more or less closely related to the Negrito, based on evidence that ranges from firm to gossamer-thin speculation.
The Internet is full of web-sites in which a wide variety of dubious propositions are offered regarding human ancestry, human races and other subjects touching on this chapter. In real science, interpretation of evidence is always tentative and subject to review if new evidence or alternative arguments turn up. Pseudo-science, on the other hand, picks out the current interpretation that suits best and denies or ignores what does not. It is rather risky, therefore, to state publicly that what we know "for certain" about human ancestry is rather less than is often thought outside the field. Researchers know this but rarely admit to it publicly. The danger is that any pedlar of pseudo-scientific snake-oil can jump in and point out "how little science really knows", thereby diverting attention from the fact that he or she knows nothing at all "for sure". We will have to live with this situation. In the spirit of real science we must admit that there is not all that much hard evidence out there yet, even if the amount is definitively growing. It also has to be admitted that much of the available hard evidence is mostly in the form of fossil bones which are subject to interpretation based on measurements. For what that means in real life see below under "Skull measurers". All this adds up to something that is definitively better than the fairy tales that we had before, but the foundations of our present knowledge remain fairly rudimentary. Unfortunately, ancient human fossils have lost all their DNA and bone measuring is still to a large extent the only method for gathering data on the subject. Keep this in mind when reading this chapter.
What follows below is based on what is, to the best of our knowledge, in line with THE MOST SOLID AVAILABLE EVIDENCE AT THE MOMENT. If new evidence or convincing alternative interpretations come to light to change or throw new light on any aspect of the subject, we will happily change this chapter. This is how real science proceeds and this is how we want to keep it.
2. Relationships at the Top Level of the tree of life
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All life forms with DNA in their cells (or cell!) are related. Even you, dear reader, are related (and not all that distantly as the following figure shows) to any DNA-carrying animal, ciliate, plant or fungi you care to mention. X you are here |
Though all life on earth is related, there are degrees of relationships, just as there are in human families where there are mother and child relationships and there are 11th cousins. The mother-child relationship is the closest and cannot be separated in time while your 11th cousin's and your own last "common ancestor" lived and died long before either of you had been born. What applies to individuals of a species also applies to entire groups from species upwards. It is only that the time spans involved are enormously larger. The degree of a relationship that any species has with any other can be seen as a function of time: the more remote a relationship = the more the DNA of the two life forms differs = the more the two life forms differ in their anatomy, requirements and and life cycle = the longer ago their common ancestor has lived.
Homo sapiens (aka "humans" or the "human race") is an earthly form of life and can be classified along with all other animals. The table reflects how closely or distantly Homo sapiens is related to other life forms.
|
Rank |
Scientific |
Description |
|
Superkingdom |
Eucariota |
Cells have nucleus |
|
Kingdom |
Animalia |
Animals |
|
Phylum |
Chordata |
Animals with notochord and dorsally situated central nervous systems |
|
Subphylum |
Vertebrata |
Backboned animals |
|
Class |
Mammalia |
Mammals (animals that nourish their young with milk) |
|
Order |
Primates |
Simians and prosimians (apes, monkeys, lemurs and other monkey-like animals) |
|
Suborder |
Anthropoidea |
Simians (apes and monkeys) |
|
Infraorder |
Catarrhini |
Old-world simians |
|
Superfamily |
Hominoidea |
Humans, apes and extinct remotely human-like forms (Oreopithecus, Afropitecus, Heliopithecus, lived more than 7 million years ago in Africa and its fringes (southern Europe, Arabia) |
|
Family |
Hominidae |
Hominids (humans and extinct human-like forms, all African) |
|
Sub-family |
Homininae |
The only living genus of the Homininae is Homo Extinct genera (all African) are Sahelanthropus,
Ardipithecus, Kenyanthropus, Australopithecus and
Paranthropus. (for Details see Fig. 34-2 below) |
|
Genus |
Homo |
All living and extinct humans extinct forms are Homo neanderthalensis, Homo
floresiensis, (for Details see Fig. 34-3 below) |
|
Species |
sapiens |
The only living species of the genus |
In our own Order Primates there are two suborders
with the following living families (we ignore the sub-classifications
between Suborder and Family here):
the Prosimii and the Anthropoidea.
The Suborder Prosimii
|
Family |
Common name |
World-wide |
Description and/or Examples |
|
Tupaiidae |
Tree shrews |
20 living |
Similar to insectivores, |
|
Lemuridae |
Lemurs |
19 living |
Madagascar primates |
|
Daubentoniidae |
Aye-aye |
1 living |
Rare, Lemur-like with spidery fingers |
|
Lorisidae |
Bush-babies |
11 living |
Includes the lorises and pottoes, |
|
Tarsiidae |
Tarsiers |
3 living |
Small, large-eyed leapers, |
|
Indriidae |
(none) |
unknown |
Lemur-like, |
The Suborder Anthropoidea
|
Family |
Common name |
World-wide |
Description and/or Examples |
|
Callitrichiidae |
Marmosets and tamarins |
21 living |
Tiny monkeys, live in |
|
Cebidae |
New-world monkeys |
26 living |
Madagascar primates |
|
Cercopithecidae |
Old-world monkeys |
60 living |
Includes baboons, langurs, rhesus, etc. |
|
Hylobatidae |
abcd |
7 living |
Gibbons and siamang, |
|
Pongidae |
Apes |
4 living |
Bonobos, chimpanzees, gorilla, orang-utan |
|
Hominidae |
Subfamily Homininae = |
1 living |
Humans |
The family Hominidae is represented by one single living species: Homo sapiens . This fact alone would not be all that unusual. Families with a world-wide distribution often have a number of species, each restricted to a special niche or geographical area. Among the truly world-wide Order Rodentia (the rodents) the Family Murridae (rats and mice) contains 500 species. If we consider invertebrate animals, we find the family Hymenoptera (bees and wasps) of the Class Insecta, there are 100,000 species. There are countless other, similar examples. What is unusual Homo sapiens is the combination of
In fact, this combination of characteristics is not just unusual, it is unique - and it can tell us a lot.
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One possible genealogical tree from cretaceous insectivores to modern Homo sapiens . Many points remain in dispute and for others the evidence is unclear or missing. The available evidence would also allow other trees to be constructed. (adapted from The Cambridge Encyclopaedia of Human Evolution, Cambridge 1992).
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Humans have not descended from monkeys - but they have a common ancestor. The chart shows the chromosomal alterations that have ocurred during the evolution of Old World Simians (infraorder Catarrhini). Each dot represents an event inferred from a comparison of the karyotypes of living species. Within any branch, the sequence of dots is arbitrary. Emphasis is given to human and great apes, whose chromosomes have been more extensively studied than those of other primates. NOR = nuclear organisers. (adapted The Cambridge Encyclopaedia of Human Evolution, Cambridge 1992). |
What the list of human peculiarities can tell us is that Homo sapiens must be a new kid on the block, a newcomer in evolutionary terms. For reasons we do not understand, apart from Homo sapiens, they all died out. For the past 30,000 years, Homo sapiens has been alone.
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Homo sapiens and its extinct relatives: some species shown here are likely to be in our direct ancestral line. Sahelanthropus tchadensis is a very recent discovery and was first described in July 2002 in Nature while Kenyanthropus platyops described in March 2001 the same magazine is scarcely less recent. (adapted and expanded from Nature, 11 July 2002, 418:134).
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A likely sequence (though far from being proven) of ancestral forms down to Homo sapiens would be according to Daniel L. Liebermann (Nature, 22 March 2001, 410:420):
from
- Australopithecus anamensis (Africa)
to
- Australopithecus garhi (Africa)
to
- Australopithecus habilis (formerly Homo habilis)
(Africa)
to
- Homo ergaster (Africa)
to
- Homo erectus (Africa, Asia, perhaps Europe)
to
- Homo SAPIENS (today world-wide)
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Details of some extinct later possible ancestors and of of early Homo sapiens itself. The archaic Homo sapiens also shown need not necessarily be in direct line of descent to modern Homo sapiens but may well represent one or several different extinct species of Homo. (Chart from: The Cambridge Encyclopaedia of Human Evolution, Cambridge 1992). |
There can be little question that the ancestral home of Homo sapiens was in Africa. A few local nationalists elsewhere still try to hold to their own theories which hold that Homo sapiens originated in their own corner of the world . The evidence for Africa is now so overwhelming that such efforts can no longer be taken seriously. The substantial available scientific evidence s all points towards Africa. What is still an open question is whether modern Homo sapiens developed exclusively in Africa or whether the species developed in a complicated series of migrations and intermingling of local forms all over Africa, Asia and possible Europe (see Robin Dennell and Wil Roebroeks An Asian perspective on early human dispersal from Africa).
The first waves of proto-human migrations are thought to have started around 1.7 million years ago. It was a splendid confirmation of this estimate when in 2002 the so-called Dmanisi skull of a Homo habilis was unearthed - in Georgia (Caucasus). Others Anatomically modern Homo sapiens itself appears first in Africa around 150,000 years ago and seems to have spread out from there in several waves from 100,000 years onwards. Whether or not Homo sapiens on his travels met the descendants of older migrations, absorbed or exterminated them during the relentless expansion, is still an open and very controversial question. No trace of older Homo DNA in the genes of modern humans has so far been found - but the search for it goes on and hopes are high that something will be found soon.
The human race is unquestionably one species under any definition of the word "species". Until around 30,000 years ago, at least one (and possibly two) other members of our genus Homo shared the planet with us: Homo neanderthalensis and (perhaps) the recently discovered tiny Homo floresiensis whose affiliation is still a matter of debate. It used to be thought that the Neanderthals were just a local variation of Homo sapiens and that the two might have interbred. Recent analysis of ancient Neanderthal mtDNA indicates otherwise: their DNA was sufficiently different for them to have been a different species, but close enough so that limited interbreeding may still have been just barely possible. It must have been rare with any offspring, if any, probably infertile, for not a trace of Neanderthal DNA has been found in modern humans.
4. Palaeoclimate and human ancestry
The following illustration is adapted from Science (Anna K. Behrensmeyer, "Climate Change and Human Evolution", Science, 27 January 2006, 311:476-478.
Marine and land records showing palaeoclimatic trends during early human evolution.
Marine record, left:
Global ice volume trend from 4.5 million years ago until today,
based on composite oxygen stable isotope data from seven marine
cores.
Marine record, right:
Cycles of aridity in the Saharan desert from 3.5 to 1.5 million
years ago, based on percent terrigenous dust in the Ocean Drilling
Program from a site in the Arabian Sea.
Land records, left:
Multibasin records of lake phases from 3.5 to 1.5 million years ago.
The darkest blue vertical bars indicate deep lakes, lighter bars
indicate shallower lakes, and the lightest bars indicate land. Red
bars mark radiometric dating levels.
Land records, centre:
Carbon stable isotope record of closed (woodland or bush) versus
open (grassland) vegetation in the Turkana basin of northern Kenya
(same basin as central lake phase record).
Land records, right:
Milestones in the fossil and archaeological record that are used as
evidence for the timing of the appearance of Homo.
There is no simple translation of the marine Plio-Pleistocene global climate shifts into the continental records, but future integration of marine and land-based evidence will allow rigorous testing of the impact of global change on th environments and evolutionary trajectories of our ancestors.
5. Speciation (the development of new species)
Environmental and other pressures (geographic, climatic and other changes, predation, parasitism, food resources, competition, etc) weigh heavily on all living things, from humans to bacteria. Over many generations, populations adapt to pressures and over long periods these changes are genetically encoded and then distributed throughout that population. Many adaptations accumulate over the generations and help make the species better adapted to its environment. If parts of a species experience somewhat different pressures to that on another part, given enough time the adaptations can make populations to break into different species.
The whole process of speciation is not well understood. One recent surprise was the discovery that parasitism and diseases are a major driving forces in speciation. Another was the discovery that while most speciation is a slow process over countless generations, there is (at least among insects and other invertebrates) the possibility of new species appearing within a few generations. Future research is likely to come up with more such surprises. Since we are concerned mostly with speciation as has affected Homo sapiens , we will disregard such complications from the world of the "lower animals".
A new species can be defined as population who has accumulated so many different local adaptations, that is has become separated from its parent population. In living population, this shows itself when the new and the old populations are no longer able or willing to produce mixed offspring. Horses and donkeys are two different species of the same genus moving apart. They can produce offspring in the artificial conditions of human care but the offspring remains infertile and cannot propagate itself: the two species have gone beyond their parting point.
Another way of recognising species is based on anatomy (especially the structure of bony parts, especially of the skull); from a somewhat arbitrary chosen moment onwards the bones of a species can be deemed deemed to be sufficiently different to form a separate species. In extinct species (including all extinct human and pre-human forms), Until someone can find a way to make bones mate, this is the only way that allows boundaries to be drawn between extinct species. Unfortunately, anatomical classification is open to differing interpretations which significantly increases the density of scientific uncertainties and controversies.
Very generally it can be said that the more species differ, the longer ago they have split off from the reference population, i.e. the longer ago lived their "common ancestor." The degree of difference cannot be used to estimate times (with the exception of mtDNA, see below) since the speed of species evolution differs unpredictably under the influence of many outside factors.
Homo sapiens is extremely long-lived by comparison with most other animals and reaches sexual maturity rather late at age 12 upwards. This slows down any genetic adaptations but humans have largely shaken off the need for genetic adaptations to survive: they now face any challenge with cultural adaptations such as tools, clothes and social cooperation. As we have seen, it took millions of years for human-like animals to develop and further hundreds of thousands of years for Homo sapiens to develop from them. A very short 30,000 years after the disappearance of our Neanderthal colleagues, we are today genetically still almost identical the Homo sapiens of those ice age days. Yet look at us today and marvel at the difference it made.
However, evolution has not forgotten us. There are local adaptations among humans called races...
6. Modern Human Races (their skin colour and body size)
Homo sapiens is today divided into a number of "races": negrid, europid, mongolid, australid, and others. The classifications of the 19th and 20th centuries (when they were fashionable) differ widely and are not worth listing here. Despite their flimsy nature, much ado has been made about all these races and their supposed deep differences (see for example our biography of E.v. Eickstedt). The appalling misery caused by such pseudo-scientific classifying among Homo sapiens during the past 200 years has been the darkest chapter in the history of pseudo-science. In fact, the genetic differences between the "human races" are minute and merely represent relatively recent local evolutionary adaptations to local conditions.
Human races exist, but only in the limited sense of an accumulation of individual genetic traits more common in people of a certain area than in others. The variations between individuals of the same race are so wide, that a majority of any population carry traits from outside their own race. There is no such thing as a "pure" race. The collection of anatomical and other traits put together to make up and define a "race" on paper is essentially arbitrary. The fact that the original inhabitants of Africa south of the Sahara are mostly naturally black does not mean they all belong into the same racial pot. For why they are black, see Fig. 35-5 below. It is not racial ties that hold groups together but social ties.
If each modern race was left alone for, say 100,000 years, to develop in isolation, we would then probably have quite a few new species in the genus Homo. But no such thing will happen. On genetic evidence, it is thought that the Andamanese Negrito were indeed isolated for tens of thousands of years but when outsiders appeared again in the 1850s, intercourse took place (whether voluntarily or not is not relevant here) and babies followed after the customary 9 months. It is an open question whether they could have developed into a separate species, even if they were left alone long enough. Their number (5,000 before the outsiders arrived in masses) and limited gene pool might have been to small, although nobody knows for sure.
The original Homo sapiens who first left Africa 100,000 years ago were probably just looking for better Although they could not have known it at the time, they set out to conquer the world. They were all black.
The modern human races (Negrids, Europids, Australoids, Mongolids, etc) are of fairly recent origin; as they look today they are less than 15,000 years old. However, to call the first modern humans to migrate out of Africa "Negrids" would be pointless since Negrids are a modern human race and did not (like all the other modern races) acquire their present detailed characteristics until 15,000 years or so ago. We do not know whether the earliest human migrants looked more like the Khoisan or like Negrids of modern Africa, or different from either. A lot can happen to one's looks in 100,000 years! What we do know is that the first migrants must have been black.
There are occasional genetic "fall-backs" of dark-skinned babies born to light-skinned parents. The opposite never happens (apart from albinos which are a different thing altogether) because black people have never been white while whites have all been black tens of thousands of years ago. The dark skinned genetic memory is still there and may occasionally be switched on to shock the snow-white parents. Pity the poor mother and baby in light-skinned societies berfore the advent of modern genetics! Not many were allowed to live then. There are also rare cases of genetic fall-backs going back even further: human babies are sometimes born with tails. Not many parents are told today when this happens and doctors are said to cut off the superfluous appendage quickly and say nothing to prevent distress to the parents.
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The flux of UV light from the sun almost perfectly matches the skin colour of the people who have lived in their present area for many thousands of years (maps from Jablonsky/Chaplin). |
Here we will look in more detail at only one racial characteristic, but that the most troublesome in all human history: skin colour.
Dark coloured skin is the result of melanin deposited in the skin. All humans produce melanin and the amount in the skin can be increased by tanning. The genetic constitution merely determines the range of skin colour variation among individuals of a given population. Lots of melanin (i.e. dark skin) offers the best protection against the ultraviolet light of the sun and in populations living for hundreds of generations in an area bathed in strong UV-light, dark skin was the required genetic standard. The "white" skin in turn was a much later adaptation of originally black populations that had gradually moved so far north that they needed as much exposure to the little UV light around to help generate vitamin D and thus avoid rickets.
Skin colour is among the most easily and rapidly changeable genetic physical traits in humans (along with hair colour, eye folds, lip and nose forms). The form of hair (as opposed to its colour), of the teeth, of bone parts and of the skull are rather slower and less predictable to change. Let a modern black group live in northern Siberia for as little as 500 generations (ca. 10'000 years) and you will have light-skinned people, do the opposite and you will get dark-skinned groups. In evolutionary terms this is practically overnight.
It is socio-cultural attitudes in genetically light-skinned societies that have first claimed that skin colour was a sign of socially low status. To the early agricultural societies, dark skin = work in fields = not high class = inferior race. Such attitudes are first recorded in pharaonic Egypt. From antiquity until the 19th and into the 20th century, Africa had been the major supplier of slave labour, from ancient Egypt, to the Romans, the Arabs right up to the early USA on the verge of the industrial revolution. The association between black skin and low status thus held over as much as 5,000 years and the catastrophic formula "dark skin = inferior" became a sort of natural law. Today we know better but Homo sapiens still has a long way to go to shake off this ancient simple-mindedness.
Another trait that needs a brief mention in a treatment of the Negrito is characteristic of a majority but not all Andamanese towards short stature (for details see Chapter 5 "A Physical Examination"). Indeed, the Andamanese are often called "pygmies" although not all are short enough to deserve the label. Nonetheless, on average they are quite short in relation to other human groups. They share the trait of shortness with populations who have lived for a genetically significant number of generations in thick forest: the African pygmies, the Veddas of Sri Lanka, the Barrineans of Australia and the other Negritos, Negritoids and Veddoids. Short stature may be an adaptation independently acquired by each population or a genetic trait going back to the original founding population - we do not know yet.
The tallest and the shortest people in the world ith the two extremes in colour (adapted from Carleton S. Coon, gratefully acknowledged):
Other genetic traits:
The trait of steatopygia (for details see Chapter 5 "A Physical Examination") links the Andamanese to the South African Khoisan (Bushmen and Hottentots) in a fascinating way: the two populations are very remote from each other but they are the only living groups with steatopygia. This is especially relevant since steatopygia is genetically controlled and is thought to be very ancient indeed.
The form of head hair and to a lesser degree other body hair (which is quite separate from hair colour) is also a racial characteristic. Whether curled or straight, the form is genetically programmed. Most African groups have tightly curled hair while outside Africa loosely curled locks and straight hair is more common. Is seems that the lose and straight hair forms have developed for unknown reasons only after the migration out of Africa.
Minute but clearly discernible differences in teeth forms, genetically controlled, distinguish some races and have become very important tracers to prehistoric migrations, especially in Asia. Teeth often survive where all other body parts including bones have long since vanished and this make them specially valuable.
7. "Skull Measurers" and "Lookers"
Until the discovery of DNA, human races were classified according to "looks". Someone "looked" Negroid, therefore he was "Negro". This was unreliable and highly subjective. Reading a book on human races of as late as the 1960s can seriously curdle one's toes today.
The "measurers" were rather more scientific than the "lookers" and bones, skulls and suchlike would be measured precisely and in in vast numbers, the variations among individuals within and outside their assigned race could still be such, however, that it was easy for classifications to become a matter of opinion - unless vast numbers of measurements could be taken of a specific population. Results and conclusions reached by reached by measuring bones (especially skull and teeth where humans are most "human") remain valid and valuable today for ancient populations, especially when complemented and checked against the results of DNA analyses.
With fossil humans, the painstaking measuring of bones and especially skulls (though with much more sophisticated technology than even 20 years ago) together with much improved dating techniques are still (almost) the only tools we have. Relationships between fossil finds can still only be established by comparing measurements. Unfortunately, fossilised bones have lost almost all their original DNA - although tiny traces left of them have indeed become increasingly recoverable with the latest DNA techniques.
All this may go some way to explain (if not excuse) the opinionated, vitriolic and often undignified disputes surrounding so many human fossils and their classification. The Australian author, T.J. Gillin, put the case nicely (in connection with the Australian aborigines and the possible existence of Australian Negritos - see our Chapter 51) when he said that "in a field where one school regards early finds as evidence of distinct "gracile" and "robust" populations, and other sees the same evidence as rival head-wear fashions, the Queensland skull issue needs to be kept in perspective."
What the old "lookers" could not accomplish and the "measurers" only in a limited way, DNA analysis can, at least in principle, supply reliable, consistent and reproducible results. The results of DNA analyses allow researchers to establish relationships between living human populations. It is even possible to establish relationships between extinct population. The methods of DNA analyses are not without its problems, of course. DNA analyses are extremely complex and have to be run through highly sophisticated computer programmes to produce intelligible results, The programmes may contain errors or analyse the data in ways that can lead to controversies between specialists using different programmes. These are essentially technological problems that can be and will be solved. There are also human stumbling blocks: many palaeontologists are comfortable with measuring and analysing bones but feel acutely uncomfortable with DNA which they do not really understand. This is a generational question that is not likely to last much beyond the current generation.
What is DNA? Every single cell of every living organism on earth &endash; from the common fly to the whale, from the bacteria to the human being &endash; has its size, function, metabolism and, besides much else, at least part of its behaviour determined by a molecule known as deoxyribonucleic acid or DNA. There are two kinds of DNA: nuclear and mitochondrial, each with its distinct advantages and disadvantages for analyses of relationships between populations.
Nuclear DNA (nDNA) is a single enormous DNA molecule inside every cell's nucleus. It is responsible for most of an organism's appearance. In humans the molecule consists of 3,000,000,000 nucleotide base pairs arranged in the form of the famous double helix into genes combining into 23 pairs of chromosomes. Only 50,000 to 100,000 (2-3%) of the whole nDNA molecule actually seem to code for making enzymes and structural protein, the rest has unknown functions and is usually known, somewhat disrespectfully, as "junk." Junk undoubtedly has some function in the evolution, replication and organisation of genes but these have not yet been discovered. Some may provide a sort of security through redundancy. There are also apparently meaningless bits of junk nDNA called introns or intervening sequences which insert themselves into genes and have to be cut out ("edited out") before the DNA message can be transcribed by the organism. Nuclear DNA is inherited from both parents and is quite stable, evolving only slowly over time. There is also only one nucleus per cell and therefore only one nDNA per cell . This makes nDNA unsuitable for using in ancient material since it is quite difficult to track down among the decayed cells of an archaeological find, for example, and because of its size it is likely to have broken into thousands of strands.
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Replication of DNA, showing how the molecule unwinds and, by pairing of the complementary bases with each other, makes two identical copies of the original DNA sequence. (from: The Cambridge Encyclopaedia of Human Evolution, Cambridge 1992). The four bases are: A (adenine) complements T (thymine) / G (guanine) complements C (cytosine). |
Mitochondrial DNA (mtDNA) got its name from its residence within the mitochondrial organelles of cells which are responsible mostly for cell metabolism and energy. In humans, the circular mtDNA is only 16,500 base pairs long and contains no junk or introns. It is inherited, at least among mammals, exclusively from the mother. On fertilisation, the mtDNA within the mother's egg is preserved while that within in the sperm cannot enter the egg and is discarded. There are several major advantages to mtDNA for studies of living populations as well as ancient remains. It is much simpler than nDNA, occurs in the thousands inside each cell and so is easily found and duplicated even from badly decayed samples. It also has parts that evolve at a speed ten times that of nDNA which makes it more useful for criminological and evolutionary studies over relatively recent time spans. Comparing two sets of mtDNA can tell us how closely two organisms are related. The remains of the victim of a crime can be positively identified on discovery, decades after death, by comparing the victim's mtDNA with that of living relatives. This has been done with murder victims, the family of the Russian Czar and with Neanderthal man, among others. It can also help to establish the relationship between living and extinct human and animal. The larger the differences between two samples, the more distant the two organisms' relationship is.
The analysis of ancient mtDNA is not another method of dating a sample although, indirectly, it can also be used in this way. Instead, mtDNA analysis is primarily a method of establishing degrees of relationships between the original owner of the sample and other individuals and groups, ancient and modern, living and extinct. How far back can reliable ancient mtDNA analysis go? Highly technical controversies have raged but nobody knows for sure. Neanderthal mtDNA more than 100,000 years old has been analysed but not all agree with the results. A great deal of research is needed before these questions can be answered with any confidence.
When we are talking about multiplication of DNA, we are talking about the survival of isolated and broken pieces of such DNA, not the survival of the complete DNA. Fanciful suggestion that long-extinct animals (or humans even) could be brought to life again through reconstructed DNA today is not even a twinkle in any serious geneticist's eyes (protestations from Hollywood notwithstanding).
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Fig.34-6a. The structure of mtDNA is circular Some genes on the mtDNA are: |
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Reprinted from Carnina Dennis "Mining the Secrets of he egg", Nature, 9 February 2006, 439:653 |
Y chromosome is not DNA but of course it contains DNA. It is the male chromosome that is switched on in embryos destined to become boys (females have chromosomes XX and males YX, hence females can be said to be female but males are really altered females, male supremacists please note). The Y chromosome is inherited from the father only and in analyses can be used as a counterpart to the all-female mtDNA to give information on the ancestral male lineage.
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The structure of the Y and X chromosomes. |
Today, DNA samples from living people are taken with a stick tipped with a cotton-wool kept in a small plastic container. Held by the stick, the cotton wool is inserted in the open mouth and then moved lightly along the inside of the cheeks for a few seconds. Then, when wet with saliva containing cells, it is re-inserted into the container, a little preservation fluid is added and the container is screwed shut - and ready is the sample for despatch to the laboratory. There is no pain, no screaming and no blood.
Even with the vastly improved technology for analysing the DNA of many human populations, it will take many years if not decades to complete the job. Many people and their governments remain highly suspicious of anything to do with DNA. They are worried what it could mean to them and if the samples they hand over could be abused or make a huge profit for someone else but not to them. In many countries, the letters DNA set off a hysteria tinged with fear of the huge pharmaceuticals, the stealing of patents and other chicanery. This is most unfortunate because none of this is true for the DNA samples taken in order to investigate the relationships of groups of people to each other.
The results can sometimes cause a certain amount of trouble when they shatter long-held myths about a population's origins. One tragic case is that of the Australian aborigines (see chapter 51). People afraid to have their group affiliations investigated with DNA analysis have to be respectfully and patiently persuaded that their myths remain valid and beautiful as myths but that their refusal to face their physical origins means living in cloud-cuckoo-land. Any refusal will have to be accepted. In the long run it will be their descendants' loss.
To set such fears at rest alone will be a major undertaking. Large gaps in our knowledge will remain. No doubt, many open questions of today will be answered, but many unexplained results will also appear. Nor is the DNA technology and the scientists using it infallible. It has always been thus. The technology of DNA analysis itself is also developing at a breathtaking rate and older results sometimes have to be re-visited and re-analysed. As before: "facts" in science remain and must remain checkable and falsifiable.
9. So, what does "Related" mean then?
"Related" in our context is the answer, backed by falsifiable scientific evidence, of when, through how many steps and in what way the genetic inheritance of the "last common ancestor" of two given populations or individuals has come down to the present day.
10. Negrito relatives Far and Wide
The following maps show that have at one time or another been thought (based on more or less solid evidence or suspicions more or less far-fetched) to be related somehow to the Andamanese Negrito. In the following chapters we will discuss these cases in more detail.
The Toalean and the Hoabinhian are stone tool industries, i.e. methods of producing and styles of stone tools in use widely in Southeast Asia between 12,000 and 6,000 years ago. The Hoabinhian is named after a site in northern Vietnam and has been suspected to have been the work of Negritoid groups (see also Chapter 25 "Prehistory").
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Fig. 34-7.
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Fig. 34-8. For numbers, see list below.
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INDIAN SUBCONTINENT and ISLANDS CONTINENTAL SOUTHEAST ASIA INDONESIA |
PAPUA AND NEW GUINEA THE PHILIPPINES AUSTRALIA The unmixed Tasmanian population has went extinct when the "last Tasmanian", the woman Truganini, died in 1876. The Kalang are an enigmatic ethnic minority people (possibly extinct) in Java who are said to have retained their ancestral religious beliefs despite centuries of Islamic domination.. |
The aboriginal and remnant populations in many countries are badly treated, despised, pushed into a precarious fringe existence and pressurised to "come into the mainstream of society" (a expression widely used in India towards the Andamanese Negrito). In practice this always gives the same result: loss of original culture without acquiring a new culture plus grinding poverty and alcoholism or drugs. While the same countries are rightly proud of their ancient past, rarely are the living representatives of that past treated with any kind of respect or allowed their dignity.
It is not a coincidence that many of the tribal names given them by outsiders mean "slave" and "debt slave" while their own names usually mean "human beings". The present-day attitude towards aboriginal populations rarely comes from ill-will but from a lack of respect which in turns comes from ignorance. Such ignorance is widespread and not limited to the less educated classes.
Only Australia and New Zealand so far have made serious efforts to make what amends are possible for the atrocities of the past 200 years. The Australian aborigines have recently received many rights long overdue to them and possession of their ancestral lands. This is good news as far as it goes, but even a good thing can be pushed into absurdity. This has been done in Australia where any archaeological find - even if it is 50,000 years old - may be claimed by the aboriginal tribe now living in the area for immediate reburial without any scientific analyses possible. One could understand if remains less than, say, 100 years old and certainly any remains personally known to the presently living must be so treated -but archaeological remains?
Political activists insist that aborigines are one people and not (perhaps) several and so research into the factual situation is strongly discouraged. Given the aborigines' treatment in the past, such reactions are only too understandable. Yet the Australian aborigines will find that they hurt themselves most when they hobble scientific research into their past. Apart from patient and respectful persuasion, there is nothing much one can do now to stop the aborigines for damaging themselves in this way . However, as soon as the first aboriginal scientists graduate, they will realise what an appalling disservice their "friendly" and politically correct academic advisors have done their parents and their people.
In the meantime, one would have thought that the academic establishment of Australia would make every effort to explain patiently and respectfully the purpose of scientific research and try to motivate the aborigines to participate in the great enterprise and in the interpretation of any results; they must be convinced, not bullied. They should also be told that their wonderful "dreamtime myths" do not clash with scientific results but that the two complement each other - there is no other place in the world where they would complement each more spectacularly! One would have thought so but one would have thought wrongly. Some scientists do try to make these points but under the dead hand of guilt-ridden "political correctness", too many do not. The attitude is widespread that results not fit for the world of PC must be false and must not be published, older results are airbrushed out of existence, denied or ignored. Obscurantist ideology in the guise of idealism comes before facts - uncles Adolf and Joe send their regards.
The problems in Australia show that treating aboriginal populations correctly anywhere and with respect is not easily done (with the best will in the world and the best laws to back it up) and may have unfortunate consequences. But it must be done with common sense and without mindless "idealism".
Our hope is that the information we present on this Web-site will go some way to change popular attitudes towards aboriginal populations in those countries that are lucky enough to still have them as citizens.
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Last change 1 February 2006
