> I'm not sure I understand what biogeography has to do with their point which seems to mainly be about the passage of time. Individuals in different biogeogra

> I'm not sure I understand what biogeography has to do with their point which seems to mainly be about the passage of time. Individuals in different biogeographical niches can have distinct “passages of time” in their immune systems, depending on their exposure to endemic pathogens. > Doesn't water mix things up pretty well? So does air, but you don’t see a homogeneous distribution of airborne pathogens around the world :) By the way, thanks for those papers, they reminded me of single-domain antibodies (or “nanobodies”), which appear to have evolved independently in cartilaginous fish and camelids: https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001120 https://journals.plos.org/plosbiology/article?id=10.1371/jou...