Yeah the ability itself is fine IMO. It is very much a pro gamer™ ability though. Depending on how it calculates there may be ways to seriously cheese it. For instance, if you use Darwin to pop +2000 science on a 4 hex natural wonder, which in turn grants you your first tech of the era, will you then get +4000 culture or does the bonus only count your per turn science?
Oh man that would be awesome as a cheese.