Natural theology originally dismissed as simplistic (5)

I believe the answer is:

naive

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'simplistic' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for naive that I've seen before include "Jejune" , "Innocently trustful" , "Unaffected or guileless" , "Rather too innocent and trusting" , "Inexperienced and guileless" .)

I've seen this clue in The Independent.

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