Harvard Professor: Do NOT Make These Health Mistakes In 2025! (Especially After 40+) | Dan Lieberman

Lieberman says humans evolved to avoid physical activity unless it is necessary or rewarding, citing studies showing fewer than 5% of people take stairs next to an escalator across cultures. He argues shame about this is misplaced.

Because humans evolved to be active, activity turns on repair and maintenance mechanisms, and without it those mechanisms are not activated to the same extent. He compares inactivity to lacking air and calls it an evolutionary mismatch.

Lieberman calls the idea that ancestral habits should be copied a paleo fantasy, noting hunter-gatherers also lack toothbrushing, vaccines and refrigeration. Their value is in revealing the normal range of human variation and the mismatches in modern life.

His ultrasound studies found habitually barefoot people have stronger foot muscles and no flat feet, while shod urban populations show weaker feet. He advises building up gradually and wearing supportive shoes during an active bout of plantar fasciitis.

He says muscle is use-it-or-lose-it and sarcopenia sets off a vicious circle of frailty, so lifting a few times a week helps. But strength training without cardio does not give the same cardiovascular benefit, as Finnish athlete data suggested.