Reading through the Prime Directive discussion, this comment got me thinking...
How many races, machines and individuals have interfered with earth's development?
And again, Humans have no clue what a pure culture looks like, since they don't come from one. They were uplifted by aliens who did play god, and apparently okay with that since they keep naming ships after them.
This is what I can think of off the top of my head.
(and the Greek gods)
(Jack the Ripper)
The 'Whale Probe
' from Star Trek IV
The 'Sky Spirit
' from Tattoo
The aliens from The '37s
I haven't even crossed into Temporal manipulation yet...
Captain Braxton and the Timeship Aeon
If you assume that the slightest interference could have big repercussions, it seems to me that the only reason humanity got to where it is, is because everyone and their brothers have dipped their toes into humanity's development.
Can you think of any other instances?