<Since fishing didn't evolve until 20,000 years ago, how did man
obtain these relatively rare fats needed for brain development if he wasn't
eating fish?>

one of the low points in this list has been the ludicrous assumption that
man could not or did not eat fish, as well as shellfish and eel, turtles,
from the word go.
throw sharp stick into water
throw saponin-containing plants into water.
throw rocks into water to make a temporary damn.
pick up shellfish from rocks.

etc
andrew