 The researchers recovered ancient DNA of Neanderthals by extracting the DNA from the femur bones of three 38,000 year-old female Neanderthal specimens from Vindija Cave, Croatia, and other bones found in Spain, Russia, and Germany.Only about half a gram of the bone samples (or 21 samples each 50–100 mg) was required for the sequencing, but the project faced many difficulties, including the contamination of the samples by the bacteria that had colonized the Neanderthal's body and humans who handled the bones at the excavation site and at the laboratory.In February 2009, the Max Planck Institute's team led by Svante Pääbo announced that they had completed the first draft of the Neanderthal genome.