One of the scariest stories exposed by Dr. Roberts was that of the chicken virus that caused appallingly large and fatal tumours. At one time, this same virus was merely a minor irritant and then a chicken vaccination had been developed - but this changed the selective landscape. The virus evolved a resistance to the drug, a change exacerbated by modern factory farming methods, and so the virus became stronger. The virus can now kill a chicken in just ten days. Of course, bacteria was on our planet long long before we arrived and no doubt, it will still be going strong when our species has disappeared.