One of the theories about what positive affect high blood sugar might have on humans- what survival advantage it could give- is that higher blood sugars help people's bodies deal with colder weather. I think the evidence for this theory is weak but I still find it interesting.
Some animals increase the concentration of sugar in their blood as part of their adjustment to colder weather.
About two years ago, somebody did a study on dolphins' insulin levels, and found that dolphins have higher insulin levels when they haven't eaten. Apparently they are insulin resistant overnight (I'll count that as a fact) which has led to some interesting speculation on the theory that people need diabetes (or rather, insulin resistance) in order to cope with low carb diets. Found that an interesting twist.