参差 itself appears in 《诗经·关雎》: 参差荇菜，左右采之 - the water-plants growing in uneven clumps. Yang Xiong's Han-era 《法言》 added 不齐 to express 'unequal level' as a judgment, and the phrase stuck.
mistakes
The pronunciation of 参差 (cēn cī, both first tone) is famously irregular - not cān (join) or shēn (ginseng), which are the character's other readings. Worth memorizing as a set.
