Tressa Jamison

The Australian Aboriginal People: 

Dating the Colonization of Australia

Abstract

The colonization of each continent by modern human populations remains an important question in our history as a species.  Studies of variations in mitochondrial genomes, Y-chromosomes, satellite DNA, and other genetic markers can be used to estimate the time of divergence of one population from another.  Recent advancements in technology have advanced our capabilities in genetic analysis.  In particular, PCR can be used to amplify, study, and sequence DNA from long-deceased specimens.

Ingman and Gyllensten studied 101 complete mitochondrial genomes from contemporary populations in Australia and many other regions.  The mitochondrial genetic diversity of Aboriginals is remarkably high, similar to that found in Asia.  Ingman and Gyllesten estimated colonization of Australia at 40,000-70,000 years ago and supported multiple waves of migration.  Another study by Adcock and others indicates that anatomically modern humans were present in Australia before complete fixation of the mtDNA lineage, but does not establish a colonization date. 

A study of Y-chromosome variation by Vandenburg and others in 1999 revealed two haplotypes unique to Australian Aboriginals.  Most (78%) of Aboriginal haplotypes fell into two clusters, possibly indicating two original, separate lineages of founding Aboriginal Australians.

As recently as the 1960’s, anthropologists predicted the colonization of Australia at less than 10,000 years ago.  Advancments in thermoluminescence dating pushed back the estimated colonization time to 50,000-60,000 years ago in the early 1990’s.  Improvements in thermoluminescence and carbon dating techniques adjusted previous colonization dates of 50,000-60,000 years to approximately 45,000 years. 

The results of morphological dating best-support the multiregional evolution hypothesis of modern humans, and further complicate the possible ancestry of modern Australian Aboriginals.

Mitochondrial DNA analysis, recent thermoluminescence dates, and the history of ocean levels coincide roughly to indicate a colonization of Australia at approximately 50,000 years ago.    

 

 

 

 

 

Introduction

 

Throughout recorded history, humans have been defined by a desire to know ourselves:  Where did we come from?  How did we get here?  Where are we going?  Many questions are directed towards our appearance as a species and subsequent populating of the earth, -- piece by piece.  One particularly large piece of the earth is Australia:  a continent, a country, and a mystery in human history.

 

Though the major events in Australian natural history have been revealed, for the most part, human history remains a great topic of debate.  Population geneticists, anthropologists, archaeologists, biologists, and theologians have agonized over the arrival of the founders of the Australian Aboriginal population since Europeans colonized Australia in the 18th century (Brown, 1997).  This paper seeks to present, discuss, and scrutinize evidence from various scientific “camps” explaining the origin of the Australian Aboriginal people.      

 

Australia’s history has been influenced by many circumstances and events.  In the last 600 million years, the continent of Australia has drifted around the globe, encountering vastly different climates, ocean levels, continental neighbors, and resident organisms.  Most recently, Australia has come to reside with neighbors of New Zealand, Papua New Guinea, various islands of the South Pacific, and Tasmania.  Focusing on the last 100,000 years, Australia’s native species have been shaped and pressured by Australia’s considerable size and extreme arid interior. 

 

The circumstances of the environment, along with population isolation and the necessary time interval, allow species on separate continents to be distinguished from one another via slight variations.  Species isolated in Australia for thousands of years display traits and variations not seen in their counterparts on other continents.  Indigenous human populations are no exception to the rule.  While one population may be phenotypically* similar to another, variations exist in genotypes which are not evident to the outward observer (Strachan and Read, 2004).  Studies of variations in mitochondrial genomes*, Y-chromosomes, satellite DNA*, and other genetic markers can be used to estimate the time of divergence of one population from another (Strachan and Read, 2004).  

 

In addition to genetic studies, archaeological and anthropological evidence can provide clues and a context on which the genetic information may be applied (Brown, 1997).  Some human remains in Australia have been dated to correlate with other evidence, or in some cases, contradict it (Brown, 1997).  Genetic and anthropological/archaeological evidence taken together may begin to explain the origin of the Aboriginal Australian people.

The Arrival of the Australian Aboriginal People

Introduction to Human Population Genetics

Recent discoveries in molecular biology and genetics have made it possible to use DNA, as opposed to morphological* features, to describe the relatedness of species and populations.  By comparing the relative similarities and differences in the DNA sequence, the divergence of species can be plotted on an evolutionary tree (Strachan and Read, 2004).  More recent population divergence can also be studied using slight variations in the genetic material.  In particular, PCR* can be used to amplify, study, and sequence DNA from long-deceased specimens (Strachan and Read, 2004; Adcock et al., 2001).

*Indicates a particular term is defined in the glossary.

 
 


Among the most commonly studied human sequences is the mitochondrial genome.  Mitochondrial DNA (mtDNA) is significant because it is passed from mother to offspring (never father to offspring) and evolves at a different rate than the nuclear genome (Strachan and Read, 2004; Ingman and Gyllesten, 2003).  Living humans are remarkably homogenous in regards to mtDNA in comparison to other species (Strachan and Read, 2004; Ingman and Gyllesten, 2003).  Still, there are some differences between populations which may be compared.

 

Sequence variation in the Y-chromosome may also be used to study human populations (Vandenburg et al., 1999).  The Y-chromosome can be seen as the male analog of the mtDNA, as the Y-chromosome is only passed from father to son (Vandenburg et al., 1999).  The Y-chromosome evolves at a different pace than mtDNA, but the two taken together may yield powerful information.

 

Population Genetics Applied to Ancient Australia

 

Recent advances in DNA technology and molecular biology have provided new insights into the colonization of Australia via examination of genetic material.  Specifically, today’s living Aboriginal Australians may be compared to ancient anthropological specimens unearthed in Australia, New Guinea, Africa, and a number of other contemporary populations to propose a time of divergence of the founding population of Australia.

*Indicates a particular term is defined in the glossary.

 
Studies of mtDNA and Y-chromosome variation are among the most commonly studied and informative.  Of particular importance is a study conducted by Ingman and Gyllensten in 2003.  Ingman and Gyllensten studied 101 complete mitochondrial genomes from contemporary populations in Australia, New Guinea, Asia, India, Europe, Melanesia, and Polynesia (Ingman and Gyllesten, 2003).  Samples were selected from a wide range of subpopulations.  Based on an estimated substitution rate for the mitochondrial coding region of 1.7x10-8 substitutions per site per year, and using modern computational/statistical methods* to develop a likely evolutionary tree, the deepest genetic divergence occurred approximately 71,000Ī12,000 years ago (Ingman and Gyllesten, 2003).  Notably, the mitochondrial genetic diversity of Aboriginals is remarkably high, similar to that found in Asia (Ingman and Gyllesten, 2003) This supports the hypothesis that Aboriginals migrated to Australia earlier in human history than first suspected (Ingman and Gyllesten, 2003).  Mitochondrial genome data indicates that Australia was colonized between 40,000 and 70,000 years ago from a heterogeneous source population or by multiple migrations of smaller groups (Ingman and Gyllesten, 2003).

*Indicates a particular term is defined in the glossary.

 
Another type of study by Adcock and others in 2001 examined mtDNA from 10 ancient Australians from several archaeological sites (Adcock et al., 2001).  The study included 4 specimens within the skeletal range of living Australians and 6 with morphologies outside the range of contemporary indigenous Australians (Adcock et al., 2001).  The Lake Mungo 3 specimen (see map next section) is the oldest (approximately 60,000 years ago, by thermoluminescence dating) “anatomically modern” human from which DNA has been recovered.  This ancient man’s mtDNA only survives as a segment inserted* into chromosome 11 of the nuclear genome, which is now widespread among human populations (Adcock et al., 2001).  This indicates that that Lake Mungo 3’s lineage probably diverged before the most recent common ancestor of contemporary human populations.  The other ancient Australian individuals have mtDNA sequences descended from the most recent common ancestor of living humans (Adcock et al., 2001).  Results indicate that anatomically modern humans were present in Australia before complete fixation of the mtDNA lineage (Adcock et al., 2001).  While this result does not establish a definite colonization period of Australia, it is a challenge to current opinions on human origins, and remains an interesting piece in the human evolutionary puzzle (Adcock et al., 2001). 

In contrast to Australian mtDNA, Australian Y-chromosome diversity is surprisingly limited.  One would expect that an isolated population would develop variations in Y-chromosome DNA in parallel with mtDNA variations.  A study by Vandenburg and others in 1999 revealed two haplotypes unique to Australian Aboriginals (Vandenburg et al., 1999).  The frequency distributions of 4 highly polymorphic Y-chromosome specific microsatellites* were determined in 79 unrelated Aboriginal males from the Northern Territory thought to be the site of earliest colonization (Vandenburg et al., 1999).  These results were compared with other worldwide populations at the locus* and haplotype* level.  Combing all 4 microsatellites produced 41 unique haplotypes.    Most (78%) of Aboriginal haplotypes fell into two clusters, possibly indicating two original, separate lineages of Aboriginal Australians (Vandenburg et al., 1999).  This is in contrast to the study by Ingman and Gyllesten, which supported multiple migrations of Aboriginal Australians. 

 

*Indicates a particular term is defined in the glossary.

 
 


Archaeology and Anthropology Applied to Ancient Australia

Anthropological and archaeological evidence may support or contradict the estimated time of colonization of Australia obtained by genetic analysis.  As recently as the 1960’s, anthropologists predicted the colonization of Australia at less than 10,000 years ago (O’Connell and Allen, 2004).  In the 1980’s, Carbon 14* dating pushed back the estimate to approximately 40,000 years ago.  Archaeologist Rhys Jones observed that this was suspiciously close to the limits of Carbon 14 dating techniques (O’Connell and Allen, 2004).  Jones’ suspicions proved justified when thermoluminescence* dating pushed back the estimated colonization time to 50,000-60,000 years ago in the early 1990’s (O’Connell and Allen, 2004; Roberts et al., 1994).     

One particular broad and very recent study by O’Connell and Allen reviewed data from over 30 archaeological sites, focusing on 5 sites with proposed ages of greater than 45,000 years (O’Connell and Allen, 2004).  Improvements in thermoluminescence and carbon dating techniques pushed forward previous colonization dates of 50,000-60,000 years to approximately 45,000 years (O’Connell and Allen, 2004). 

On current evidence, 45,000 calendar years is the best outside date for the colonization of Pleistocene Sahul. It requires more than the mere announcement of yet another old date, without adequate consideration of context, to change this conclusion” (O’Connell and Allen, 2004). 

*Indicates a particular term is defined in the glossary.

 
To review, archaeologists in the 1960’s dated the colonization of Australia at about 10,000 years ago (O’Connell and Allen, 2004).  Carbon 14 dating pushed this estimate back to about 40,000 years ago in the 1980’s (O’Connell and Allen, 2004).  Thermoluminescence dating in the 1990’s pushed the colonization back further to approximately 50,000-60,000 years ago (Roberts et al., 1994).  And most recently, improvements in dating techniques adjusted the estimate to approximately 45,000 years ago (O’Connell and Allen, 2004).  Perhaps further advances in archaeological dating techniques are required to solve this mystery.  See Figure 1 below for prominent archaeological sites in Australia and Southeast Asia, including the Lake Mungo site mentioned in the previous section.

Figure 1:  Significant archaeological sites in Sahul* and adjacent parts of southeast Asia (Brown, 1997).

*Indicates a particular term is defined in the glossary.

 
 


In addition to dating specimens, anthropologists look to morphological features to date human remains.  One particular specimen of importance is WLH50, recovered from a deflating land surface in the Garnpung/Leaghur Lakes region of southwestern New South Wales (Brown, 2004; Hawks et al., 2000).  This fragmentary cranial vault is the source of considerable controversy.  In 1987 the specimen was Carbon 14 dated as “modern” (Brown, 1997).  In 1991 the specimen was dated older than Lake Mungo remains on morphological grounds (Brown, 1997). Electron spin resonance estimates the specimen to be 30,000 years old (Brown, 1997).  This specimen is of considerable importance because various theories of human evolution make different predictions about its ancestry (Hawks et al., 2000), namely the complete replacement hypothesis and the regional evolution hypothesis.  Researchers used metric and non-metric data from three specimens that are potential ancestors of WLH50 to test predictions of WLH50’s ancestry (Hawks et al., 2000).  The results best-support the multiregional evolution hypothesis of modern humans, and further complicate the possible ancestry of modern Australian Aboriginals (Hawks et al., 2000). 

*Indicates a particular term is defined in the glossary.

 
In direct disparity, a study conducted in 1999 (previous to the study by Hawks and others) asserts that evidence collected from WLH50 as supportive of multiregional evolution is unreliable (Antón and Weinstein, 1999).  This study concludes that it is unwise to use non-metric traits, such as cranial contours, to infer relatedness between fossil Australians and other hominids of that time (Antón and Weinstein, 1999).  According to the study, the frequency of non-metric traits may be influenced by artificial deformation and pathological hypervascularity/hyperostosis* (Antón and Weinstein, 1999).   Peculiarly, the study by Antón and Weinstein preemptively and specifically contradicted the study by Hawks and others.  This is just one indication of the disagreement among archaeologists/anthropologists on the colonization date of Australia and related human history.      

Conclusions

Though genetic, archeological, and anthropological studies on the colonization date of Australia are contradictory at times, some general conclusions may be reached when the evidence is considered collectively. 

Based on mtDNA analysis, Ingman and Gyllesten proposed a colonization date of 71,000Ī12,000 years ago and suggested multiple migrations to Australia or a heterogeneous source population. Vandenburg and others did not suppose a colonization date, but based on Y-chromosome analysis suggested two distinct waves or colonies of founding Aboriginal Australians.  The most recent and reliable thermoluminescence dates support the estimated colonization of Australia at approximately 45,000 years ago (O’Connell and Allen, 2004).  Morphological studies in general have supported the multiregional model of human evolution (Hawks et al., 2000), and hence have not supported a colonization date because these models assert that humans arose independently in Australia.

*Indicates a particular term is defined in the glossary.

 
The range of Ingman’s and Gyllesten’s study (40,000-70,000 years ago) coincides roughly with O’Connell’s and Allen’s estimate of colonization at 45,000 years ago.  Brown points out that sea levels dropped around 50,000 years ago (Brown, 1997) and would enable humans to migrate to Australia without large ocean obstacles (see Figure 1 on page 8).  Although more evidence is necessary to declare a definite establishment date of Australia’s native human population, Aboriginal Australians may justifiably presume a history of about 50,000 years.  Improvements in genetic analysis (undoubtedly on the way), advancements in thermoluminescence dating, and the discovery of additional human specimens will help to clarify this colonization date.     

 

 

 

 

 

 

 

 

 

 

 

 

REFERENCES

 

Adcock, G J; Dennis, E S; Easteal, S; Huttley, G A; Jermiin, L S; Peacock, W J and Thorne, A.  2001.  Mitochondrial DNA sequences in ancient Australians:  Implications for modern human origins.  Proceedings of the National Academy of Sciences of the USA.  98(2): 537-42.  

 

Antón, Susan C and Weinstein, Karen J.  1999.  Artificial cranial deformation and fossil Australians revisited. J. of Human Evolution. 36(2): 195-209.

 

Brown, Peter.  1997.  Australian Palaeoanthropology.  History of Physical Anthropology:  an Encyclopedia.  F Spencer, ed.  New York, NY.  Garland Publishing.  138-145.             

 

Hawks, John; Oh, Stephen; Hunley, Keith; Dobson, Seth; Cabana, Graciela; Davalu, Praveen; Wolpoff and Milford H.  2000.  An Australasian test of the recent African origin theory using the WLH-50 calvarium.  J. of Human Evolution. 39(1): 1-22.

 

Horton, David, ed.  1994.  The Encyclopaedia of Aboriginal Australia:  Aboriginal and Torres Strait Islander History, Society, and Culture.  Canberra, Australia.  Aboriginal Studies Press.

Ingman, M and Gyllesten, U.  2003.  Mitochondrial genome variation and evolutionary history of Australian and New Guinean aborigines.  Genome Research.  13(7): 1600-6. 

 

Merriam-Webster Online Dictionary, http://www.m-w.com/netdict.htm.  Accessed on 03/11/2004. 

 

Mitchell, R J; Howlett, S; White, N G; Federle, L; Papiha, S S; Briceno, I; McComb, J; Schanfield, M S; Tyler-Smith, C; Osipova, L; Livshits, G and Crawford, M H.  1999.  Deletion polymorphism in the human COL1A2 gene: genetic evidence of a non-African population whose descendants spread to all continents.  Human Biology.  71(6): 901. 

 

Mitchell, R J.  1998.  Y-chromosome-specific restriction fragment length polymorphisms (RFLPs): relevance to human evolution and human variation. American J. of Human Biology.  8(5): 573-586.

O’Connell, J F and Allen, J.  2004.  Dating the colonization of Sahul (Pleistocene Australia–New Guinea): a review of recent research. J. of Archaeological Science, In Press, Corrected Proof.  Available online 17 January 2004 via www.sciencedirect.com.

Roberts, Richard G; Rhs, Jones; Spooner, Nigel A; Head, M J; Murray, Andrew S and Smith, M A.  1994.  The human colonization of Australia: optical dates of 53,000 and 60,000 years bracket human arrival at Deaf Adder Gorge, Northern Territory. Quaternary Science Reviews. 13(5-7): 575-583.

                        

McConvell, Patrick and Evans, Nicholas, eds.  1997.  Archaeology and Linguistics:  Aboriginal Australia in Global Perspective.  New York, NY.  Oxford University Press.

 

Strachan, Tom and Read, Andrew P.  2004.  Human Molecular Genetics:  Third Edition.  New York, NY.  Garland Science.  275-310. 

 

Vandenburg, N; van Oorshot, R A; Tyler-Smith, C and Mitchell, R J.  1999.  Y-chromosome-specific microsatellite variation in Australian aboriginals.  Human Biology. 71(6): 915-31.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

GLOSSARY

 

Carbon 14 dating- the determination of the age of old material (as an archaeological or paleontological specimen) by means of the content of carbon 14 (Merriam-Webster Online). 

Computational/statistical methods to develop evolutionary trees-involves generating most likely trees, most simplistic trees, and statistical techniques to predict an evolutionary tree from a set of data (Ingman and Gyllesten, 2003).

Haplotype- a set of genes that determine different antigens but are closely enough linked to be inherited as a unit; also : the antigenic phenotype determined by a haplotype (Merriam-Webster Online). 

Hypervascularity- excessive growth relating to a channel for the conveyance of a body fluid, especially blood vessels (Merriam-Webster Online)

Hyperostosis- excessive growth or thickening of bone tissue (Merriam-Webster Online)

Locus- the position in a chromosome of a particular gene or allele (Merriam-Webster Online). 

Mitochondrial genome-the complete set of DNA contained and maintained by mitochondria in the cells of eukaryotes. 

 

Morphology- “a : a branch of biology that deals with the form and structure of animals and plants b : the form and structure of an organism or any of its parts.”  (Merriam-Webster Online)

Nuclear inserts-DNA inserted into the nuclear genome and perpetuated by replication, may consist of transposons or other sequences (Strachan and Read, 2004). 

PCR-Polymerase Chain Reaction:  “Usually designed to permit selective amplification of a specific target DNA sequence within a heterogeneous collection of DNA sequences.”  (Strachan and Read, 2004)

 

Phenotype- “the visible properties of an organism that are produced by the interaction of the genotype and the environment.” (Merriam-Webster Online)

Sahul- “Sahul is the continent formed when glacio-eustatically lowered sea levels exposed dry land connections between Australia, New Guinea and Tasmania.” (O’Connell and Allen, 2004).  

 

Satellite DNA-“sequences whose base composition is significantly different to that of the bulk DNA” (often repeated sequences). (Strachan and Read, 2004)

            Also mini- and microsatellite DNA (smaller repeated sequences)

Thermoluminescence dating-

 the determination of the date at which materials were formed by measuring the light energy released when heating it (http://en.wikipedia.org/wiki/Thermoluminescence_dating)