Wondering about extras casting

I have this on laser disc; it's fascinating. The strange, animated books are a unique experience.

I've always wondered about casting this for the nude extras.
-Did they get a surplus of candidates willing to bare it all frontally?
or
-Were they forced to accept whoever was basically presentable and willing?

If they got a surplus then they must have been picking and choosing on some criteria. A Wikipedia article states tersely:
'"The film is also notable for its extensive use of nudity, displayed with a naturist ethos in keeping with the work's key themes. (i.e. The nude actors and extras represent a realistic cross-section of male and female humanity.)"[citation needed]'
Note the "citation needed" disclaimer.
It's been a while since I saw it, but as I recall the selection was all white and contained a fair number of plain-Janes and plus-size types. They were not predominantly Hollywood cutie types, so the "realistic cross-section" claim above seems appropriate, with the added qualification of "Caucasian".

That plainness may have been a tactic to avoid accusations of pornography.
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