Sunshine, Pathogen Genocide, Vitamin D, Happiness, and Cognition

Immunology has long fascinated me. Somewhere, sometime I read how the immune system was so sensitive it could identify a self from non-self protein in as little as 10 amino acids. "Crap!" I internally exclaimed even though completely ignorant of immunology at that time. As it turns out ...

Sort of true. That is a class of molecular structures known as PAMPS: pathogen associated molecular patterns.  Charles Janeway is the poster boy on that front. Our innate immune system is sensitized to these patterns. When you crunch numbers in a crude off the top sort of way, the immune system does a remarkably good job at fending off pathogens that have certain mathematical advantages. The challenge is so great that evolution came up with(remarkably!) the heavy and light chains which allow a tremendous ongoing creation of antibody types until there is one that "fits". It is a numbers game and while there are good odds with microbes the odds are bad with viruses because their replication and mutation rates are, relatively speaking, much higher. Two modern viruses are excellent examples of this. Hepatitis C and HIV exist in a variety of variants that will keep expanding. So when you think of mass extinctions remember one viable cause is a tiny molecular structure of only two key components which can wipe out a species very quickly and leave no trace. It dies with the species. That is an unsuccessful virus and not our concern. We are concerned with all the bugs that manage to live on and in us.