If less hair helped, why didn’t humans become fully hairless?

Answer: Some hair still helped

Some hair still helped ✓ — Correct! Humans did not simply lose hair everywhere. Hair stayed where it still helped, such as on the scalp, eyebrows, and eyelashes.

Evolution stopped halfway — Wrong. Evolution does not aim for a perfect endpoint. Traits stay when they still provide useful functions.

Hair was too costly — Wrong. The issue was not that hair was simply too costly, but that different body areas faced different pressures.