In the case of the Double-Helix, it's understandable, since they communicate through smell (and phermones, whatever they might be). However, the Nephilem do speak, so it's reasonable to assume they have history - where there's communication, there's history. Except that they might not have writing, which would then mean that their history comes in the form of legends, and is much vaguer than human history.
Or they might have a hive mind, like it is implied in the WCP manual.