Evidence of ancient antibiotic resistance genes in bacteria

"Researchers Find Antibiotic Resistance in Ancient DNA"

link to NYTimes article

Highlights

• researchers isolated and sequenced DNA from bacteria in 30,000 yr old permafrost
• by comparing the gene sequences to current databases they were able to identify some of the ancient genes as genes involved in antibiotic resistance

for current Micro students - so given that 30,000 years precedes human use of antibiotics (considerably I might add), why did those bacteria have antibiotic resistance genes? (let me know if you think you have an answer...you'll find out later this semester but it's an interesting one to think about in the meanwhile.)