What killed the Orcadians was not dietary deficiency but disease. People living together are vastly more likely to spread illness from household to household, and the close exposure to animals through domestication meant that flu (from pigs or fowl), smallpox and measles (from cows and sheep), and anthrax (from horses and goats, among others) could become part of the human condition, too. As far as we can tell, virtually all of the infectious diseases have become endemic only since people took to living together.
