A review in Science argues that sugars from fruit and honey, not meat, powered the human brain

The authors argue that the roughly fivefold expansion of the hominin brain over about four million years, from roughly 300 g in early hominins to about 1,500 g in modern humans, was underwritten by dietary sugars from fruit and honey rather than by meat, the story that has dominated popular accounts for decades.

They model obligatory glucose demand, meaning glucose required by brain, red blood cells, kidney medulla and reproductive tissue, across six evolutionary stages including australopithecines, Homo habilis and Homo erectus. As reported in coverage, the brain takes about 20% of resting energy in adults and around two thirds of basal metabolic rate in developing children, with modelled adult glucose requirements in the range of 150 to 250 g per day and around 125 g for children.

Supporting evidence spans fossil dental morphology and wear, isotope ratios, comparative primate diets, trichromatic color vision as an adaptation for spotting ripe fruit, and genetic variation in sugar and starch metabolism. Raw starch releases very little glucose without cooking or processing, and grinding stones for flour appear only about 65,000 years ago, long after brain expansion was underway, which is why naturally sweet foods carry the argument.

Press coverage also reports a claim that early hominins derived more than 65% of energy from sugars in fruit and honey. That figure is unverified against the paper.

The numbers

Brain mass expansion, as reported in coverage	roughly 300 g in early hominins to about 1,500 g in modern humans, across about four million years
Adult brain share of resting energy, as reported	around 20%; developing children around two thirds of basal metabolic rate
Modelled glucose requirement, as reported	150 to 250 g per day for adults, around 125 g for children
Reported claim on early hominin energy from sugars	more than 65% from fruit and honey, unverified against the paper
Earliest evidence of seed grinding for flour	about 65,000 years ago

What this does not show

That the paper's numbers are confirmed. The Science article page returned a 403 to every access attempt during the digest sweep. Volume, issue, pages, DOI and date are confirmed from PubMed indexing, but the specific figures come from press coverage and need checking against full text.
New evidence. This is a review. Nothing was measured; it is an argument built from other people's data, and it is explicitly a corrective to a prevailing narrative, which means it is arguing a side.
Anything about modern diets. A paleoanthropology argument about honey and ripe fruit says nothing about added sugar in a modern diet, and evolutionary arguments are weak guides to optimal intake for a person with a desk job.
That sugars replaced meat. The sugars not meat framing is a media construction as much as an authorial one. The paper's own position is that carbohydrate belongs alongside meat, fat and protein in the picture, not that it replaces them.
That honey intake was measured. Honey leaves almost no archaeological trace, so its contribution is inferred rather than measured, and diet reconstruction across millions of years is loosely constrained by isotope and dental evidence.
That glucose is dietarily essential. Obligatory glucose demand can be met by gluconeogenesis as well as by diet. The argument is about the metabolic cost of that route, a distinction that gets lost fast in summary.

Caveats worth holding

Verification limit: the Science article page returned a 403 to every access attempt during the sweep, so all specific numbers here come from press coverage of the paper rather than from the paper itself. Verify against full text before repeating any of them.
It is a review, not new evidence, and it is explicitly arguing against a prevailing narrative.
Diet reconstruction across millions of years is inherently uncertain; honey in particular leaves almost no archaeological trace.
Amylase copy number variation is frequently cited in this debate and is genuinely contested in the genetics literature.
Nothing here supports any claim about added sugar, modern diets or health.