No evidence anywhere of a straight line in nature.

"Nature uses an organizing principle - it never uses a straight line," Harman said. "I've never seen any evidence anywhere of a straight line in nature - nothing. Your cardiovascular system: 60,000 miles long and no straight pipes, and it's far more efficient than anything humans have ever dreamt of."

(PAX Scientific)

Crystal structures use

Crystal structures use straight lines I believe, or don't they count :-)