Extraction of the mitochondrial DNA After death, DNA starts degrading immediately. It is thought that under the most favorable conditions, some DNA fragments can survive for as long as 50,000 to 100,000 years. The Feldhofer Neandertal fossil, thought to be between 30,000 and 100,000 years old, was therefore pushing the limits for this kind of work. Howeverinitial testing of the fossil showed good preservation of amino acids, indicating that it might contain recoverable mtDNA. Polymerase Chain Reaction (PCR) is a techniquewhich can be used to create many copies of an initially small number of molecules.
The researchers used PCR to amplify and extract many short strands of mtDNA from

the Neandertal sample. By overlapping these, they were able to generate a sequence of 379

bases apparently from the Neandertal individual. To protect against errors and

contamination, each base was extracted in at least two separate amplifications. Krings et

al. then compared this sequence against a database of 994 different mtDNA sequences from

modern humans. For the sequence of mtDNA in question, humans on average differ from each

other in 8 +/- 3.1 positions (the '3.1' represents one standard deviation). The greatest

difference between any two modern humans was 24, and the smallest difference was 1 (because

duplicates were removed from the database). Distributions of Pairwise Sequence Differences

among Humans, the Neandertal, and Chimpanzees. X axis, the number of sequence differences; Y

axis, the percent of pairwise comparisons. (Krings et al, 1997) By contrast, the Neandertal

genome had an average of 27 +/- 2.2 differences from modern humans  The smallest difference

between any human and the Neandertal was 22, and the largest difference between any human

and the Neandertal was 36.