about 500 million years ago, a split occurred, resulting in what would evolve into two major immune system lineages. One lineage belongs to non-jawed vertebrates, such as the lamprey and the hagfish. They developed a defense network that is both fundamentally different from ours and nearly as sophisticated. By comparison to ours, theirs is like an ancient language with different lettering, an alternate scripting of the genetic code that confers many of the same defense advantages.
