Why does everyone cite "The Chase", when the proliferation of humanoid species by The Preservers was already explained two decades earlier in "The Paradise Syndrome"?
In fact, it amazes me that "The Chase" even got past story development meetings. Did NOBODY on staff watch the original series?
The writers of the "The Chase" left the issue vague, but Ron Moore has said that it was their intention that the race depicted probably was the Preservers.
The reason that people are more inclined to use "The Chase" is probably because that episode specifically addresses the biological similarities between Trek races. The only information that we had on the Preservers was that they saved potentially endangered cultures. We saw no evidence that they had any role in spreading humanoid biology or that they might have had any connection between say the Vulcans, Romulans, Klingons etc.