To know what the heck I’m speaking about, we could have to rapidly assessment what the TNG episode “The Chase” was all about.
In that ep, Captain Picard’s mentor and father determine, Professor Galen, dies, leaving his former scholar with a research-based thriller to unravel.
Ultimately, the Enterprise captain (with the assistance of Klingons, Cardassians, and even Romulans) solves the thriller. They discover a recording from an historic race claiming to be answerable for seeding the galaxy with the DNA that led to the formation of those alien races (which explains why all of the aliens are comparatively much like people).