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Fossils tell you what an extinct relative looked like. They cannot tell you whether that relative is still, in a small way, inside you. Svante Pääbo found a way to ask that question, by reading DNA from bones tens of thousands of years old. This post covers who he is, the problems ancient DNA throws up, what his team found, a worked example that turns "1-4% of the genome" into base pairs, and what students can take from his approach.
Who is Svante Pääbo?
His Nobel Prize facts page records that he was born on 20 April 1955 in Stockholm. He received the 2022 Nobel Prize in Physiology or Medicine alone, "for his discoveries concerning the genomes of extinct hominins and human evolution". At the time he was at the Max Planck Institute for Evolutionary Anthropology in Leipzig.
The 2022 Nobel press release adds that he began working on Neanderthal DNA as a postdoctoral researcher with the evolutionary biologist Allan Wilson, moved to the University of Munich in 1990, and was later offered the chance to set up the Max Planck Institute in Leipzig.
Why is ancient DNA so hard to read?
The press release lists the problems. Over time DNA is chemically modified and breaks into short fragments. After thousands of years only traces are left, and those traces are heavily contaminated with DNA from bacteria and from present-day humans.
Pääbo's first answer was to start small. Mitochondria have their own small genome, present in thousands of copies per cell, which raises the chance that some survives. In 1997 his group reported in Cell a stretch of mitochondrial DNA from the original Neanderthal specimen80310-4), found in 1856 in western Germany. Multiple controls showed the sequence belonged to the fossil, not to contamination. It fell outside the range of modern human variation.
What did the Neanderthal genome show?
Pääbo then went after the much larger nuclear genome. In 2010 his team published a draft sequence of the Neanderthal genome in Science, made from more than 4 billion nucleotides from three individuals. Neanderthals shared more genetic variants with present-day people in Eurasia than with people in sub-Saharan Africa. The best explanation was that Neanderthals and the ancestors of non-Africans had interbred.
The press release puts numbers on it: in people of European or Asian descent, about 1-4% of the genome comes from Neanderthals. It also dates the most recent common ancestor of Neanderthals and Homo sapiens to around 800,000 years ago.
Who were the Denisovans?
In 2008 a finger bone about 40,000 years old was found in Denisova Cave in southern Siberia. Its DNA was well preserved. Pääbo's team reported in Nature that its complete mitochondrial genome belonged to an unknown hominin. The press release says the sequence was unlike all known Neanderthal and modern human sequences, and the group was named Denisova. Some people in Melanesia and other parts of South East Asia carry up to 6% Denisovan DNA.
How much DNA is 1-4%? A worked example
NCERT's Class 12 chapter on the molecular basis of inheritance gives the haploid content of human DNA as 3.3 × 10^9 base pairs.
At 1%: 0.01 × 3.3 × 10^9 = 3.3 × 10^7 bp, or 33 million base pairs.
At 4%: 0.04 × 3.3 × 10^9 = 1.32 × 10^8 bp, or 132 million base pairs.
For comparison, NCERT gives E. coli's whole genome as 4.6 × 10^6 bp. Even the low end, 3.3 × 10^7 bp, is about 7 times that (3.3 × 10^7 / 4.6 × 10^6 = 7.2).
So the Neanderthal share in a single person is small as a percentage but very large as DNA.
Common mistakes:
Using the diploid figure. Percentages of "the genome" refer to one set, so use 3.3 × 10^9, not 6.6 × 10^9.
Saying Africans have zero Neanderthal DNA. The finding is that non-Africans share more; be careful with absolutes.
Mixing up dates. NCERT says Neanderthals lived 1,00,000 to 40,000 years ago in the near east and central Asia; the Nobel press release gives a wider range, from about 400,000 to 30,000 years ago, across Europe and western Asia. Use NCERT's figures in your exam, and know that research gives a fuller picture.
What can a student take from Pääbo's way of working?
Start with the version you can solve. He tackled small, many-copy mitochondrial DNA before the full genome.
Assume your own sample is contaminated. His controls are why the results were believed.
Bring in other skills. The press release says he worked with experts in population genetics and sequence analysis.
His work rests on copying tiny amounts of DNA, which links it to our story of Kary Mullis and PCR, and NEET students can revise the fossil side in our guide to human evolution. For genome arithmetic like the example above, the Fermi Problem Library has worked problems with a step-by-step solver that explains the reasoning rather than printing an answer.
Try it now: work out how many base pairs 6% of a human haploid genome is, and compare it with your answer for 4%.
