DNA is particularly well preserved in hair — enabling the genome of a human to be sequenced, and his ancestry and appearance to be determined, from 4,000-year-old remains.

The impact of the Human Genome Project (HGP)1 and the development of 'mega-DNA sequencers' continue to have ramifications in diverse fields. An excellent example is reported on page 757 of this issue by Rasmussen et al.2, who describe the first genome sequence of an ancient human. Their work was made possible only by the technical advances seen since the HGP. The authors used bioinformatics tools, databases and molecular-biology techniques to uncover a great deal of information about this ancient person.

Rasmussen et al.2 recovered DNA from a tuft of 4,000-year-old human hair preserved in permafrost at Qeqertasussuk, Greenland. The hair came from an individual from the Saqqaq culture, the first culture known to inhabit Greenland. On the basis of their DNA analysis, the authors identified the individual as a male. They also determined that, surprisingly, the geographical origin of the man was eastern Siberia, thereby providing insights into the peopling of the New World. Finally, the authors reconstructed some of the features and characteristics of this individual. We predict that many future studies will also combine methods for analysing ancient DNA with the scientific tools and genomic information that have accumulated as a result of the HGP. Such studies have the potential to reconstruct not only our genetic and geographical origins, but also what our ancestors looked like.

DNA analyses of ancient humans and their ancestors have always been technically challenging, from the initial work on an Egyptian mummy3 to the more recent sequencing of Neanderthal DNA4. Typically, these studies have been conducted on bone or skin tissue. The main difficulty with such work is that almost all excavated ancient tissues are contaminated with modern human DNA, not to mention substantial numbers of fungal and bacterial colonies4,5,6. Several measures can be taken to enrich ancient human DNA, such as taking multiple samples of the same specimen, or analysing only short DNA fragments that have the characteristic damage associated with ancient genetic material5,6.

Studies on mammoths7, however, show that DNA in hair is typically preserved with little contamination from fungi or bacteria. Rasmussen et al.2 therefore extracted the DNA from the Saqqaq specimen in the expectation that it would have retained mostly human DNA. Sure enough, they found that more than 84% of it came from the ancient human. They then used the latest 'next-generation' sequencing technology to generate 20× coverage of most of the ancient genome (79% of the genome was sequenced 20 times; the genome consists of 3 billion base pairs). This is impressive, given that the gold standard for the HGP was 10× coverage.

The authors' next step was to study the genome's single nucleotide polymorphisms (SNPs) — differences at single DNA base pairs that exist between individuals (Fig. 1). These genetic markers are spread relatively uniformly across the human genome, and can provide, among other data, information on the geographical origin of an individual. Such data are especially useful in this instance2, because the origin of the Saqqaq culture has been hotly debated. Most theories propose that the Saqqaqs' ancestors were migrants from neighbouring Native American populations, such as the Na-Dene of North America or the Inuit of the New World Arctic. Figure 1: Single nucleotide polymorphisms of an ancient genome. V. WARD, UNIV. AUCKLAND Rasmussen et al.2 have sequenced the genome of a man from the Saqqaq culture, using DNA from hair preserved in permafrost in Greenland. They analysed the genome to find single nucleotide polymorphisms (SNPs) — differences in single DNA base pairs that exist between individual genomes, and that may act as markers of an individual's physical traits. a, Here, a short stretch of human DNA is shown that is a marker for normal earwax. b, In the analogous DNA from the Saqqaq individual, there is a SNP in which a C in the lower strand has been replaced by a T (C, G, T and A denote the four kinds of DNA base). This SNP shows that the Saqqaq man had dry earwax. Rasmussen and colleagues identified other SNPs indicating that the ancient human had, among other things, brown eyes, non-white skin, thick dark hair and an increased susceptibility to baldness. Full size image

Rasmussen et al.2 analysed more than 350,000 SNPs from the ancient genome, comparing them with SNP data of people from several surrounding populations to pinpoint the geographical origin of the Saqqaq individual. Surprisingly, the ancient eskimo proved to be most closely related to three Old World Arctic populations: the Nganasans, Koryaks and Chukchis of the Siberian far east. This suggests that there was a substantial and relatively recent migration across the Bering Strait and over North America to Greenland (see Fig. 3a on page 761). The authors' analysis indicates that the Saqqaqs diverged from the Chukchis about 200 generations (5,400 years) ago, implying that the ancestral Saqqaqs separated from their Old World relatives almost immediately before their migration to the New World.

Human SNPs are now known to number in the millions, and many of them have been identified as reliable markers for an individual's phenotype (characteristics)8. Rasmussen et al.2 used DNA databases to match large numbers of their Saqqaq individual's SNPs to the likely phenotypes of individuals in modern human populations that carry the same SNPs. In this way, the authors were able to provide a wealth of information on their subject's morphology, metabolism and a likely predisposition (Fig. 1). They determined that their individual was an inbred male with a pattern of population-defining SNPs commonly found among east Siberians, and that he had an A+ blood group, brown eyes, non-white skin, thick dark hair and 'shovel-graded' front teeth typical of Asian and Native American populations. What's more, he had an increased susceptibility to baldness, dry earwax and a metabolism and body-mass index commonly found in those who live in cold climates.

With a growing number of SNPs being linked to morphological or physiological characteristics9,10,11, we have an increasingly powerful forensic tool with which to 'reconstruct' extinct humans and the demographics of populations. This will also allow high-resolution analyses of worldwide population movements, on a scale not previously seen: future studies will probably be able to track movements more broadly across both space and time.

But it won't all be plain sailing. One big problem is that the majority of ancient human remains are found in temperate and even hot environments. Because the rate of degradation of ancient DNA increases exponentially with temperature, it remains to be seen whether genomic studies of hominin specimens from these regions will recover sufficient DNA to be informative. Whatever the case, Rasmussen and colleagues' findings2 will no doubt stimulate a series of additional studies and provide useful methods for future investigations of human evolution.

References 1 International Human Genome Sequencing Consortium Nature 409, 860–921 (2001). 2 Rasmussen, M. et al. Nature 463, 757–762 (2010). 3 Pääbo, S. Nature 314, 644–645 (1985). 4 Green, R. E. et al. Nature 444, 330–336 (2006). 5 Wall, J. D. & Kim, S. K. PLoS Genet. 3, e175 (2007). 6 Green, R. E. et al. EMBO J. 28, 2494–2502 (2009). 7 Miller, W. et al. Nature 456, 387–390 (2008). 8 Ioannidis, J. P. A., Gilles, T. & Daly, M. J. Nature Rev. Genet. 10, 318–329 (2009). 9 HUGO Pan-Asian SNP Consortium Science 326, 1541–1545 (2009). 10 Cruciani, F. et al. Am. J. Hum. Genet. 70, 1197–1214 (2002). 11 Tishkoff, S. A. Science 324, 1035–1044 (2009). Download references

Author information Affiliations David M. Lambert and Leon Huynen are in the School of Environment and the School of Biomolecular and Physical Sciences, Griffith University, Nathan, Queensland 4111, Australia. d.lambert@griffith.edu.au David M. Lambert & Leon Huynen l.huynen@griffith.edu.au David M. Lambert & Leon Huynen Authors David M. Lambert View author publications You can also search for this author in PubMed Google Scholar Leon Huynen View author publications You can also search for this author in PubMed Google Scholar

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About this article Cite this article Lambert, D., Huynen, L. Face of the past reconstructed. Nature 463, 739–740 (2010). https://doi.org/10.1038/463739a Download citation Published: 10 February 2010

Issue Date: 11 February 2010

DOI : https://doi.org/10.1038/463739a