Brain

Cooked starch fed the growing human brain

By WhyStopHarmingAnimals.com

The popular story says eating meat made us smart. The evidence points to starch[1][2][4]. Humans carry a genetic adaptation for digesting starch[4][5] that other apes lack, the foods that feed most of humanity are grains, tubers and pulses[9][10], and researchers who study human evolution argue that glucose from plants, above all cooked starch, fuelled the brain as it grew[1][2]. Plenty of other animals eat meat, and none of them became human-smart.

The brain runs on glucose

Hardy, Brand-Miller, Brown, Thomas and Copeland set out the case in the Quarterly Review of Biology in 2015[1]. Cooking starch greatly increased the energy reaching glucose-hungry tissues, the brain most of all[1], and they argue plant starches were essential during the Pleistocene, when the brain was expanding. Our ancestors did eat meat[1]. So do hyenas, wolves and orcas, and none of them grew a 1,350-gram brain.

In 2026 Brand-Miller, Hardy, Copeland and colleagues returned to the question in Science, modelling the human body’s glucose needs back to four million years ago[2]. Sugars from fruit and honey came first[2], then pounded and cooked starch once fire was in use[2]. As the University of Sydney put it in its coverage of the paper, raw starch does not release glucose[3], so early humans probably relied on sweet plant foods until cooking made tubers and grains useful[3]; after that, cooked starch from wild yams and similar plants contributed[3]. The authors conclude that glucose was essential for the human brain, which puts carbohydrate foods in the bigger-brain story as much as animal foods[2].

These are reviews and modelling papers, not experiments, and nobody can run a controlled trial on human evolution. Their argument rests on physiology and on what the genome and the world’s diet show.

Our genes adapted to starch

Perry and colleagues reported in Nature Genetics in 2007 that humans carry about three times as many copies of AMY1, the gene for salivary amylase, as chimpanzees on average, and that populations eating more starch carry more copies still[4]. Behringer and colleagues (Physiology & Behavior, 2013) measured salivary amylase across the apes and found much higher levels in humans than in the other great apes[5], in line with earlier reports that put the human figure around six to eight fold higher[5]. Dogs and some rodents later expanded their own amylase after generations of eating human starch[5]. Cats barely have it[5].

Humans have no comparable gene expansion for digesting raw flesh. The enzymes that break down protein, pepsin and trypsin, work on protein from any food, plants included, and herbivores make them too. Without tools, cooking and seasoning, flesh is hard to chew and mostly bland. The genome invested in starch[4], and it took a kitchen to make meat easy to eat.

Stomach acid is sometimes offered as proof that humans are built for meat. Beasley and colleagues (PLOS ONE, 2015) found human stomach acid runs at about pH 1.5[7], and the rabbit, a herbivore, has a comparably acidic stomach in the same dataset[7]; scavengers as a group run lowest[7], and cats sit around 3.6. Stomach acid alone does not make a species a carnivore[7]. Milton Mills, writing on comparative anatomy, points to our grinding molars[8], the lack of the shearing carnassial teeth that cats have[8], a small intestine long relative to a cat’s, and a colon built to hold plant bulk.

What humans eat, everywhere

The FAO lists the foods most people live on as rice, wheat, maize, millet, sorghum, potatoes, cassava and yams[9]. Rice, maize and wheat alone provide about 60% of the world’s food energy[9], and starch staples including pulses supply the bulk of calories for most of the species[10]. Cooked grain and tuber as a global primary diet is something no other animal has[10]. No wolf or orca lives on rice[9].

Carnivores hold no monopoly on intelligence

If eating meat were what builds intelligence, the animals we call smart would mostly be meat-eaters. Sentient Media compiled a widely shared list of 30 animals often called the most intelligent[11]. It is journalism rather than a scientific ranking[11], but it works as a rough check. About seven of the 30 eat almost only animals: dolphins, octopuses, cats, orcas, wolves, hyenas and Portia spiders[11]. About eleven eat almost only plants: elephants, African grey parrots, pigeons, horses, squirrels, bees, deer, llamas, koalas, gorillas and giraffes[11]. Chimpanzees, bonobos and orangutans, also high on the list, get the vast majority of their calories from plants.

A diet of meat does not explain intelligence in other animals[11], and the genes and staple foods of our own species point to starch[4][9][10].