Diseases causation Complexity

In our increasingly complex world, as we encounter thousands of unnatural toxins, typically in varying combinations, every person becomes a relatively unique specimen unto him- or herself, one that cannot be replicated in a laboratory setting. The best we can do is look for instances where a large population has been exposed to an agent. So while MDs love certainty and want to provide =definitive diagnosis, many areas of medicine today still rely on a wait-and-see, or maybe-this is-causing-that, or let's-see-if this-works-at-all approach. In fact, in many cases we have no idea what is causing a particular syndrome, disease or epidemic. We just notice that unexpectedly someone is sick for no apparent reason. (from How Does evolution really work now? Juan Enriquez and Steve Gullans 2015)