A short, fossilized femur from a 38,000-year-old Neandertal could lead to the first full genome sequence for the closest relative of Homo sapiens. Working off samples from the same bone, two research groups used different methods to obtain partial DNA sequences and compared them with human DNA. The two genomes are at least 99.5 percent identical (in comparison, chimpanzees share 99 percent of the human genome). Depending on the particular genetic analysis, humans and Neandertals split from a common ancestor perhaps about 500,000 to 700,000 years ago, and the two stopped interbreeding about 370,000 years ago. The Neandertal sequence will help answer lingering questions, such as whether humans who migrated out of Africa mated with Neandertals in Europe 30,000 to 40,000 years ago. The current studies did not find any evidence of such mixing, but they did not rule out the possibility. The findings appear in the November 16 Nature and the November 17 Science.