IPA: /ˌrɛtrəˈɡrɛʃən/
KK: /rɛtrəˈɡrɛʃən/
A process of returning to a simpler or less developed state, often involving decline or deterioration.
The retrogression of the species was evident as their habitat was destroyed.
Retrogression → It is formed from "retro-" (meaning backward) and "gressio" (from "gradi", meaning to step or walk). The word describes the act of stepping backward or returning to a previous state.
Think of 'going backward' ('retro-') as if you are 'stepping' ('gressio') back in time — that's what retrogression means.