The Fat Accep­tance move­ment may seem like a 21st cen­tu­ry phe­nom­e­non, ris­ing to pub­lic con­scious­ness with the suc­cess of high-pro­file writ­ers, actors, film­mak­ers, and activists in recent years. But the move­ment can date its ori­gins to 1967, when WBAI radio per­son­al­i­ty Steve Post held a “fat-in” in Cen­tral Park, bring­ing 500 peo­ple togeth­er to protest, cel­e­brate, and burn diet books and pho­tos of Twig­gy. “That same year,” notes the Cen­ter for Dis­cov­ery, “a man named Llewe­lyn ‘Lew’ Loud­er­back wrote an arti­cle for the Sat­ur­day Evening Post titled, ‘More Peo­ple Should be FAT.’” These ear­ly sal­lies led to the found­ing of the Nation­al Asso­ci­a­tion to Advance Fat Accep­tance (NAAFA) two years lat­er and more rad­i­cal groups in the 70s like the Fat Under­ground.

There would be no need for fat activism, of course, if there were no bias­es against fat peo­ple. This rais­es the ques­tion: where did those bias­es come from? They are not innate, says Har­vard Uni­ver­si­ty evo­lu­tion­ary biol­o­gist Daniel Lieber­man in the Slate video above, but are a prod­uct of a his­to­ry that tracks, coin­ci­den­tal­ly, with the rise of mass mar­ket­ing and mass con­sumerism. We have been sold the idea that thin bod­ies are bet­ter, health­i­er, more attrac­tive, and more desir­able, and that fat is some­thing to be warred against. “How­ev­er, as an evo­lu­tion­ary biol­o­gist, “says Lieber­man, I’ve come to appre­ci­ate that with­out fat, we’d be dead. Humans wouldn’t real­ly be the way we are. Fat is real­ly life.”

A quick perusal of art his­to­ry shows us that larg­er bod­ies have been val­ued around the world in much of human his­to­ry. We now asso­ciate fat with poor health, but it has also sig­naled the oppo­site — a store­house of caloric wealth and healthy fer­til­i­ty. “Our bod­ies have all sorts of tricks to make sure we nev­er run out of ener­gy,” says Lieber­man, “and the main way that we store ener­gy is fat.” Leiber­man and oth­er biol­o­gists in the video sur­vey the role of fat in human sur­vival and thriv­ing. “Fat is an organ,” and sci­en­tists are learn­ing how it com­mu­ni­cates with oth­er sys­tems in the body to reg­u­late ener­gy con­sump­tion and feed our com­par­a­tive­ly enor­mous brains.

Among ani­mals, “humans are espe­cial­ly adapt­ed to be fat.” Even the thinnest among us are cor­pu­lent com­pared to most pri­mates. Still, the aver­age human did not have any oppor­tu­ni­ty to become obese until rel­a­tive­ly recent his­tor­i­cal devel­op­ments — in the grand evo­lu­tion­ary scheme of things — like agri­cul­ture, heavy indus­try, and the sci­ence to pre­serve and store food. When Euro­peans dis­cov­ered sug­ar, then mass pro­duced it on plan­ta­tions and export­ed it around the world, sug­ar con­sump­tion mag­ni­fied expo­nen­tial­ly. The aver­age Amer­i­can now eats 100 pounds of sug­ar per year. The aver­age hunter-gath­er­er might have strug­gled the eat “a pound or two a year” from nat­ur­al sources.

The over-abun­dance of calo­ries has led to a type-II dia­betes epi­dem­ic world­wide that is close­ly relat­ed to sug­ar con­sump­tion. It isn’t nec­es­sar­i­ly relat­ed to hav­ing a larg­er body, although fat deposits in the heart and else­where can wors­en insulin resis­tance (and heart dis­ease); the prob­lem is almost cer­tain­ly linked to excess sug­ar, the con­stant avail­abil­i­ty of high-calo­rie foods, and low incen­tives to exer­cise. Our hunger for sweets and love of com­fort are not char­ac­ter flaws, how­ev­er. They are evo­lu­tion­ary dri­ves that allow us to acquire and con­serve ener­gy, oper­at­ing in a food econ­o­my that often pun­ish­es us for those very dri­ves. Diet­ing not only does­n’t work, as neu­ro­sci­en­tist San­dra Aamodt explains in her TED Talk above, but it often back­fires, mak­ing us even hun­gri­er because our brains per­ceive us as deprived.

As sci­en­tists like Lieber­man gain a bet­ter under­stand­ing of the role of fat in human biol­o­gy, those in the med­ical com­mu­ni­ty are real­iz­ing that doc­tors and nurs­es are hard­ly free from the soci­etal bias­es against fat. Stud­ies show those bias­es can trans­late to poor­er med­ical care and bad advice about diet­ing, a vicious cycle in which health con­di­tions unre­lat­ed to weight go untreat­ed, and are then blamed on weight. Evo­lu­tion­ary biol­o­gy explains the role of fat in human devel­op­ment, and human his­to­ry explains its increase, but the ques­tion of where the hatred of fat comes from is a trick­i­er one for these sci­en­tists to answer. They bare­ly men­tion the role of adver­tis­ing and enter­tain­ment.

In 1979, activists in the “Fat Lib­er­a­tion Man­i­festo” iden­ti­fied the prob­lem as fat people’s “mis­treat­ment by com­mer­cial and sex­ist inter­ests” that have “exploit­ed our bod­ies as objects of ridicule, there­by cre­at­ing an immense­ly prof­itable mar­ket sell­ing the false promise of avoid­ance of, or relief from, that ridicule.” Despite decades of resis­tance, the diet indus­try thrives. A Google search of the phrase “body fat” yields page upon page of unsci­en­tif­ic advice about ide­al body fat per­cent­ages, as though remind­ing the major­i­ty of Amer­i­cans (7 in 10 are clas­si­fied as over­weight or obese) that they should feel there’s some­thing wrong with them.

Blame, shame, and ridicule won’t solve med­ical prob­lems, say the biol­o­gists in the video above, and it cer­tain­ly doesn’t help peo­ple lose weight, if that’s what they need to do. If we bet­ter under­stood the role of fat in keep­ing us healthy, hap­py, and alive, maybe we could over­come our hatred of it and accept oth­ers, and our­selves, in what­ev­er bod­ies we’re in.

Relat­ed Con­tent: 

How the Food We Eat Affects Our Brain: Learn About the “MIND Diet”

Exer­cise May Prove an Effec­tive Nat­ur­al Treat­ment for Depres­sion & Anx­i­ety, New Study Shows

Why Sit­ting Is The New Smok­ing: An Ani­mat­ed Expla­na­tion

Josh Jones is a writer and musi­cian based in Durham, NC. Fol­low him at @jdmagness