Sugar, Not Just Meat, Powered the Human Brain's Evolution, Study in Science Argues

Meat has long dominated the story of how the human brain grew, but a new study published in Science argues the expansion ran on a dual fuel: meat and sugar. The multi-centre study, by Jennie Brand-Miller, professor of human nutrition at the University of Sydney's Charles Perkins Centre, and colleagues does not discount meat's role, but posits that natural sugars and starch found in fruits and honey delivered the glucose — the simple sugar that fuels body tissues — required to power a rapidly expanding, metabolically expensive brain.

Over roughly four million years, the human brain grew from around 300 grams in early hominins — early two-legged human ancestors — to about 1,500 grams in modern humans. As brains grew, so did demand for glucose, which is also needed by red blood cells, kidneys and reproductive organs. The researchers modelled the glucose needs of humans and their ancestors from four million years ago until recently, and the modelling suggests sugars provided over 25 percent of dietary energy.

Brand-Miller explained that raw starch will not release glucose, meaning early humans likely relied on naturally sweet foods long before cooked grains entered the diet. The earliest hominins such as "Lucy", whose brain was the same size as a chimpanzee's, along with Homo habilis and Homo erectus, were likely highly reliant on carbohydrate-rich foods, particularly fruit. Only later, as fire and cooking became widespread, did starch from underground food sources such as wild yams, water lily rhizomes and African potato contribute to glucose intake.

Co-author Karen Hardy, professor of prehistoric archaeology at the University of Glasgow, said: "The human evolutionary diet has a strong focus on meat eating and the need for protein. But we also require energy and this is best provided by glucose obtained from plants." Meat still provided critical amino acids and micronutrients, the study holds, and the findings might also explain to some extent why humans crave sweet foods.