Before I get lambasted the out off Africa model is also just a theory I believe fish is optimal food for humans incl shellfish hypothesis iv read claim bipedilism evolved from wading. Modern Apes stand on 2 legs in swamp forests to cross water, humans have many coastal adaptations brown fat and white fat less hair kidneys that excrete excess salt. Brains that thrive on DHA fats and good swimming capabilities it's possible we were sea hunters then conquered land in that order there's to many adaptations to write here but Google is your friend thoughts?