The moratorium on la bise, as it’s known in France, brings sorrow, but also relief
parasitic agents (meaning infectious bacteria, fungi, parasitic invertebrates, and viruses) only exist if they’ve managed to avoid their host’s immune system, at least long enough to replicate and send their next generation on to a new host. No infectious agent is descended from an ancestor that was killed before it could replicate. In fact some parasitic agents can have geologically long relationships with their host species such that the two are really coevolved. Despite the evolution of a multifaceted immune system, parasitism is a fundamental principle of life. […]
Plants and the vast majority of animals on earth have no acquired immune system; rather, they have a multiplicity of mechanisms to prevent infection that we collectively term innate immunity. I wish to emphasize that the most effective innate mechanism is the denial of access. […]
Why is innate immunity sufficient for the most abundant species on earth, but not for vertebrates? […]
The proposal here is that contrary to widely held views of practicing immunologists, the immune system is not evolutionarily selected to prevent infection in an absolute sense. Rather, it is selected to make one individual slightly more resistant or at least different than others of the same or related species. The adversary of any individual is not really the world of parasites, they are truly undefeatable, it is his or her neighbor. A zebra doesn’t have to outrun the lion, just the slowest member of the herd.
