Nature is weird, so I don't consider it impossible for the body to attack itself. Obviously, that condition has to be rare or difficult to trigger; otherwise it

Nature is weird, so I don't consider it impossible for the body to attack itself. Obviously, that condition has to be rare or difficult to trigger; otherwise it would have evolved out, unless it would come with great benefits in other features. One explanation could be that our living conditions have changed sufficiently to trigger the erroneous behavior more frequently. There are various proposals for factors, ranging from mundane (e.g. dirt) to crazy, of course. Another one could be that the immune system attacks things that are no longer there, either because the system gets stuck, or because those things looked too much like our own tissues. Or indeed, we're overlooking something. The latter is a difficult one, and won't get much attention, because the risk of not finding anything publishable is too high.