An archaeologist of the genome: Svante Pääbo
Submitted by brown on 23 August 2011
How, I ask, did he get into this field of research? He explains that an early fascination with Egypt, fuelled by holidays there with his mother, led him to study Egyptology at the University of Uppsala, Sweden. There, however, his romantic dreams were dashed: “We learned about ancient Egyptian word forms, rather than excavating mummies and pyramids in Egypt as I had imagined.” Disappointed, he decided to study medicine instead, and then started a PhD in molecular immunology.
The lure of Egypt persisted, however. In the 1980s, DNA sequence analysis was just beginning. Surely, thought Svante Pääbo, someone must have tried to extract and analyse DNA from Egyptian mummies? “I knew from my Egyptology studies that there are thousands of mummies in museums and hundreds more discovered every year in Egypt.
Inspired by the success of the research, which showed that Ötzi’s mitochondrial DNA (see diagram below) was very similar to that of modern central and northern European populations (Handt et al., 1994), Svante Pääbo moved further back in time – about 38 000 years into the past. He wanted to use DNA analysis to investigate human origins.
The entire set of genetic instructions found in a cell is known as the genome. In humans, the genome consists of 23 pairs of chromosomes found in the nucleus (the nuclear genome), as well as a small chromosome found in the cells’ mitochondria (the mitochondrial genome). These chromosomes, taken together, contain approximately 3.1 billion (3,1x109) bases of DNA sequence.
Nuclear DNA is inherited from both parents: each parent contributes one chromosome to each pair, so that offspring get half of their chromosomes from their mother and half from their father.
In contrast, mitochondria, and thus mitochondrial DNA, are passed from mother to offspring
Image courtesy of Darryl Leja, NHGRI / NIH
“One of the big insights from this field in the past 20 years is that modern humans came from Africa rather recently,” Professor Pääbo explains. Although many fewer people live in Africa than outside Africa, “if we look at variations in the DNA sequences of humans, we find that most of the variation exists in Africa and everybody outside Africa is a subset of that variation. It turns out that within the past 100 000 years, a group of Africans left Africa and colonised the rest of the world. So I like to say that from a molecular genomic point of view, we’re all Africans; either we’re living in Africa or we’ve been recently exiled.”
But modern humans, Homo sapiens, were not the only humans around at the time. Roaming Europe and western Asia (the Near and Middle East) from around 300 000 to 30 000 years ago were our relatives: the Neanderthals, H. neanderthalensis.
The results were fascinating: non-African modern humans carry some DNA sequences that are similar to Neanderthal sequences but are not found in Africans. In fact, the scientists’ data suggest that between 1 and 4% of the genome of non-Africans is derived from Neanderthals (Noonan et al., 2006).
“The simplest explanation is that when modern humans first left Africa, they came through the Middle East and then went on and colonised the rest of the world. In the Middle East, modern humans interbred with Neanderthals, and their descendants carried the Neanderthal DNA sequences with them – to Australia or Papua New Guinea or the Americas,” explains Professor Pääbo. Only the African populations were unaffected (see diagram below).Svante Pääbo believes that when modern humans first left Africa, they came through the Middle East, interbred with Neanderthals, and then colonised the rest of the world, carrying Neanderthal DNA sequences with them
Image courtesy of Nicola Graf
“What’s so fascinating to me is that with DNA sequence analysis, we can answer questions that we cannot address by looking at the skeletons of early humans or the stone tools that they left behind.”
Since 1997, true to his early fascination for human origins, Professor Pääbo has been a director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
ESRF is one of the members of EIROforumw4, the publisher of Science in School.
Currently, Professor Pääbo is working on an even more distant human relative than the Neanderthals. And at first glance, he and his colleagues had very little to go on: just the tip of a little finger bone, found in southern Siberia. The scientists knew that this bone belonged to some sort of hominid – or human form – but initially they knew very little more about it. What did it look like? How widespread was it? Could it have been a type of hominid found right across Asia while the Neanderthals were limited to more western regions?
Whereas the last common ancestor of Neanderthals and modern humans lived half a million years ago, the mystery hominid diverged from the Neanderthal-human ancestor about a million years ago. That small fragment of bone belonged to a very distant human relative indeed.
This is the first time that a new hominid has been described purely by its DNA sequence but, believes Svante Pääbo, such analyses will become increasingly popular. “This little bone fragment has hardly any information about what the individual looked like, but if it’s well enough preserved, our next step will be to reconstruct the whole genome from it. I think that in future, we will describe newly discovered organisms by their DNA rather than by how they looked.”
This article is based on an interview with Svante Pääbo at the European Molecular Biology Laboratory in June 2010.
Handt O et al. (1994) Molecular genetic analyses of the Tyrolean ice man. Science 264(5166): 1775-1778. doi: 10.1126/science.8209259
Kozlowski C (2010) Bioinformatics with pen and paper: building a phylogenetic tree. Science in School 17: 28-33. www.scienceinschool.org/2010/issue17/bioinformatics
Macchiarelli R et al. (2006) How Neanderthal molar teeth grew. Nature 444: 748-751. doi:10.1038/nature05314
Noonan JP et al. (2006) Sequencing and analysis of Neanderthal genomic DNA. Science 314(5802): 1113-1118. doi: 10.1126/science.1131412
Pääbo S (1985) Molecular cloning of ancient Egyptian mummy DNA. Nature 314(6012): 644-645. doi: 10.1038/314644a0
Rau M (2010) Science is a collective human adventure: interview with Pierre Léna. Science in School 14: 10-15. www.scienceinschool.org/2010/issue14/pierrelena
Smith TM et al. (2010) Dental evidence for ontogenetic differences between modern humans and Neanderthals. Proceedings of the National Academy of Sciences of the United States of America 107(49): 20923-20928. doi: 10.1073/pnas.1010906107
w1 – For a virtual tour of the new building at the European Molecular Biology Laboratory (EMBL), Europe’s flagship laboratory for basic research in molecular biology in Heidelberg, Germany, see: www.embl.de/events/atc/tour
w2 – An international research centre in Grenoble, France, ESRF produces high-brilliance X-ray beams, which serve thousands of scientists from all over the world every year. To learn more, see: www.esrf.eu
w4 – For more information about EIROforum, see: www.eiroforum.org
To find out more about some of Svante Pääbo’s work on primate evolution, see the entertaining fictional dialogue between the ancient Greek philosopher Democritus and his student: www.embl.de/aboutus/science_society/writing_prize/2002_jekely_brochure.pdf
For more about what our DNA can tell us about human evolution, see the following articles by one of Svante Pääbo’s recent PhD students:
For a review of a fictional account of the Neanderthals, see:
To find out how X-ray studies at ESRF can cast a light on the evolution and migration of more distant human ancestors, see:
For more information about ‘Ötzi’, see the website of the South Tyrol Museum of Archaeology, where the iceman is preserved: www.iceman.it
To browse the Science in School evolution series, see: www.scienceinschool.org/evolution
If you enjoyed this article, you might like the other feature articles in Science in School. See: www.scienceinschool.org/features
Dr Eleanor Hayes is the editor-in-chief of Science in School. She studied zoology at the University of Oxford, UK, and completed a PhD in insect ecology. She then spent some time working in university administration before moving to Germany and into science publishing, initially for a bioinformatics company and then for a learned society. In 2005, she moved to the European Molecular Biology Laboratory to launch Science in School.
Cutting-edge science is not just about the future – modern technology can also deepen the understanding of the past. This article about how the study of the genome contributes to archaeological research used in biology lessons to interest students in genetics and evolution. It could also form the starting point of some interdisciplinary research linking biology and history, perhaps using ‘Ötzi’.
Suitable comprehension and extension questions include:
The article could also be used as the basis of discussions, for example about:
Betina da Silva Lopes, Portugal