Question: Is modern clinical antibiotic use responsible for the emergence of antibiotic resistance in bacteria?
Bacterial (ancient) DNA was isolated from 30,000 (!) year-old Beringian permafrost sediments. As with many aDNA studies - there's the problem of contamination. To establish authenticity (I found this part really neat), they amplified 12S rRNA and two chloroplast genes, then BLASTed the amplified fragments to ensure that the sequences matched late Pleistocene (not Holocene - the present geological epoch) flora and fauna. Once authenticity was established, they looked for the presence of resistance-conferring genes in these aDNA bacterial genomes - specifically resistance genes for tetracycline, penicillin, and vanomycin (as a side note, they also looked at genes responsible for "diverse strategies of drug evasion").
The big finding? The ancient bacteria already possessed genes conferring antibiotic resistance - highly similar to the genes we see in modern bacteria. Antibiotic resistance is ANCIENT. And not something that evolved via selection pressures caused by modern clinical antibiotic use.