Cows. They've been blamed for the Great Chicago Fire, for blowing up barns with their flatulence and for plunging towns into darkness by rubbing electrical poles [sources: AP; BBC]. But thanks to a genetic analysis of tuberculosis DNA taken from a trio of 700- to 1,000-year-old Peruvian skeletons, they might at long last be in the clear for a more serious crime: originating the bacterium that later jumped species to cause tuberculosis in humans. According to research published in the Aug. 20, 2014, issue of Nature, that dubious distinction now belongs to seals [sources: Bos et al.; Saey].
Actually, the pinnipeds didn't so much originate the disease as transport it to the New World. The new research suggests that TB originated in Africa about 4,000 to 4,400 years ago and produced seven strains, some of which jumped to animals and then later back to humans. The seal explanation is supported by the fact that ancient Peruvians used tools made from seal remains and depicted seals and seal hunting on their pottery [source: Doucleff]. The theory helps to explain how they could have become infected with TB when no land route to the New World existed at the time [sources: Bos et al.; Saey].