primitive man; prehistoric human
Refers to early humans or hominids from prehistoric times, often in anthropological or historical contexts. Can also be used figuratively to describe someone with crude or unsophisticated behavior.
I saw a fossil of a primitive human at the museum.
His rough behavior is just like that of a primitive man.
古代人 means 'ancient people' and typically refers to humans from early historical civilizations, whereas 原始人 points to pre-civilization, Stone Age humans.
Compound of 原始 (primitive, original) and 人 (person). The term is a modern coinage used in anthropology and history to describe early humans.