IPA: /ˌjuːnɪˈvɑːlvd/
KK: /junˈivəld/
Not developed or changed; remaining in a simple or primitive state.
The unevolved species still exhibits traits from millions of years ago.
Unevolved → It is formed from "un-" (meaning not) and "evolve" (from Latin "evolvere", meaning to unroll or develop). The word "unevolved" means not developed or not having undergone evolution.
Think of 'not' ('un-') having 'developed' ('evolve') — that's why unevolved means something that has not changed or progressed.