Genomic Sequencing of Pleistocene Cave Bears -- Noonan et al. 309 (5734): 597 -- Science:
Despite the greater information content of genomic DNA, ancient DNA studies have largely been limited to the amplification of mitochondrial sequences. Here we describe metagenomic libraries constructed with unamplified DNA extracted from skeletal remains of two 40,000-year-old extinct cave bears. Analysis of ~1 megabase of sequence from each library showed that despite significant microbial contamination, 5.8 and 1.1% of clones contained cave bear inserts, yielding 26,861 base pairs of cave bear genome sequence. Comparison of cave bear and modern bear sequences revealed the evolutionary relationship of these lineages. The metagenomic approach used here establishes the feasibility of ancient DNA genome sequencing programs.
Direct comparison of modern bear DNA and DNA from bears roughly 42-45,000 years old reveals that Brown bear (grizzly) and polar bear both split off from a common ancestor more recent than the cave bear lineage. The cave bears are not necessarily that common ancestor, and the common ancestor may be older than 45,000 years old.