Western disgust at eating insects may have roots deeper than culture — dental plaque from 745 ancient humans found Europeans rarely ate them, while genetic evidence shows reduced ability to digest their exoskeletons persisted for at least 9,000 years.

Disgust can feel instinctive even when it is culturally learned. For many Western diners, a cricket or mealworm on a plate crosses a line that prawns, oysters and blue cheese do not. Yet insects are ordinary foods in many parts of the world, which raises a difficult question: when did the divide begin?

A 2026 study in Science Advances looks far beyond recipes and etiquette. Researchers searched ancient dental calculus for insect DNA, then examined modern and ancient human variants near two genes that help the stomach digest chitin, the tough carbohydrate in insect exoskeletons.

The two records point in the same broad direction. Ancient Homo sapiens from northern Eurasia carried very little convincing insect DNA, while genetic variants associated with lower stomach expression of chitin-digesting enzymes were already established at least 9,000 years ago. The study does not identify a gene for disgust or prove that biology caused a cultural taboo. It suggests that Western avoidance may rest partly on an older ecological and dietary history.

Ancient tartar became a record of possible meals

Dental calculus is mineralised plaque. As it hardens on a tooth, it can preserve microbial and dietary molecules for thousands of years. That makes it valuable, but not perfectly clean: DNA can come from deliberate food, an insect swallowed with water, material introduced after death or contamination during excavation and storage.

The researchers compiled 1,028 sequencing libraries from the AncientMetagenomeDir database and another published dataset. They represented calculus from 745 anatomically modern humans, mostly ancient Europeans, plus 18 Neanderthals. The oldest Homo sapiens samples reached back about 33,000 years.

A custom reference database contained 10,761 insect mitochondrial genomes. The team used a Bayesian screening tool to identify possible matches, then imposed additional tests for species specificity, read abundance and the fragmentation expected of ancient DNA. For comparison, the same pipeline examined calculus from 57 gorillas and 39 chimpanzees with better documented diets.

Only ten ancient human samples produced validated species-level insect traces: eight Homo sapiens and two Neanderthals. Across all 745 modern-human individuals, read abundance was far below that seen in gorillas, western chimpanzees and Neanderthals.

Most Homo sapiens traces did not look like deliberate insect meals

The identity of the insects mattered as much as their scarcity. Calculus from a roughly 29,500-year-old individual in what is now the Czech Republic contained DNA from a nonbiting midge whose larvae live in lake sediment. The authors considered accidental ingestion in drinking water more plausible than collecting the insect as food.

A German individual dating to about 9,200 years ago and an Egyptian mummy contained insects associated with damp buildings or stored products. Those traces could reflect contaminated grain, later museum exposure or errors made while calculus was sampled. Mummies and preserved skeletons carried the greatest diversity, including beetles associated with decomposing bodies.

One case exposed the problem particularly clearly. Calculus from a 42,800-year-old Neanderthal excavated in Belgium contained DNA from the harlequin ladybird, an Asian species introduced into Europe only in the late twentieth century. Whatever route it took, that DNA was not a Palaeolithic meal.

The finding is a warning for ancient-diet research. Dental calculus is not always a sealed time capsule, and the mere presence of a food species cannot automatically be translated into consumption. Even under the most generous interpretation, insect DNA was nearly absent from Homo sapiens calculus. The authors conclude that deliberate entomophagy was rare in northern Eurasia and that occasional ingestion was often incidental.

Neanderthals carried a stronger but still incomplete signal

Neanderthal samples contained more insect DNA, at an overall level comparable to western chimpanzees that use insects as a dietary supplement. Flies and mosquitoes were prominent. One Neanderthal produced two validated species, including a moth fly whose larvae can feed on late-stage decaying material.

The paper connects that pattern to an existing hypothesis: Neanderthals may sometimes have stored animal carcasses in ponds or marshy ground, creating access to fly larvae and other insects. Mosquito-rich DNA would fit a wet setting. It does not establish that behaviour from dental plaque alone, and just 18 Neanderthal individuals were screened.

ScienceBlog’s earlier review of how archaeology reconstructs Neanderthal life describes the same evidentiary difficulty. Isotopes, tools, animal bones and molecular traces can make one explanation more likely without preserving anything like a written menu.

The genetic comparison added an intriguing match. The small number of sequenced Neanderthals and the single Denisovan included in that part of the analysis carried variants associated with higher chitin digestibility. That alignment supports the dietary interpretation, but the archaic sample is too small to define every Neanderthal or Denisovan population.

CHIA and CTBS showed unusually strong latitude patterns

The second half of the study did not examine plaque. It focused on two members of the chitinase gene family. CHIA encodes acidic chitinase, which is secreted into the stomach lumen and begins breaking chitin apart. CTBS encodes chitobiase, an enzyme expressed in stomach cells that processes a product of that breakdown.

Using genomes from 2,396 people in 26 present-day populations, the researchers tested whether variant frequencies changed with distance from latitude 8° north, a rough global centre of insect consumption and abundance. They controlled for shared population history so that ancestry alone would not be mistaken for natural selection.

Both gene regions stood out. Their latitude associations ranked in approximately the 99.47th and 99.96th percentiles of more than 12 million genome-wide tests. Variants favoured near the tropics were linked through expression data to higher CTBS activity in the stomach, while the selected CHIA region contains elements that regulate transcription.

This is functional inference, not a digestion trial. The study did not feed insects to people carrying different variants or measure how much chitin each person absorbed. “Reduced ability” means a population-level genetic predisposition toward lower expression of the relevant stomach enzymes, not a complete inability to eat insects.

The genetic divide survived 9,000 years of migration

To look backward, the team used 1,663 ancient genomes from a major reconstruction of selection in ancient Eurasia. The frequencies of two CHIA and two CTBS haplogroups remained broadly steady across the past 9,000 years, despite the major migrations and population replacements that accompanied farming and later steppe expansions.

All 130 expression-linked CTBS variants available in those ancient genomes pointed toward reduced stomach expression in Eurasian populations. The pattern was especially common in Jomon foragers from Japan, suggesting that it preceded the agricultural transition rather than being created by farming.

The team’s Institute of Evolutionary Biology summary frames low insect availability outside the tropics as the likely starting point. Insects provide an efficient caloric return when social species such as ants or termites can be gathered in bulk. Where that biomass was less dependable, there would have been less advantage in maintaining high chitin-digesting capacity.

The direction of causation remains reconstructed. Reduced consumption could relax selection for digestive enzymes, while lower enzyme expression could make an insect-heavy diet less comfortable or efficient. The evidence establishes an old geographic association; it does not recover the first moment northern humans stopped seeking insects.

Evolutionary history is not a gene for Western disgust

The study measured DNA, not revulsion. It did not ask modern participants whether they would eat a cricket, compare childhood exposure or test religious and culinary traditions. Present-day “Western” societies are internally diverse, and hundreds of millions of people elsewhere eat insects without sharing one cuisine or genetic profile.

Genes also do not fix a menu. Food processing can remove chitin or break it into more digestible forms. Grinding, cooking and using insects as ingredients change texture and visibility, while industrial separation can preserve protein without requiring consumers to digest an intact exoskeleton. The researchers explicitly note that these methods can bypass the proposed limitation.

Nor does the paper establish that an insect-based food is automatically sustainable, nutritious or safe for every person. Those questions depend on species, production methods, allergens, contamination and the rest of a diet. This was a study of ancient consumption and evolutionary genetics, not a clinical trial or environmental life-cycle assessment.

The careful conclusion is more interesting than either cultural or biological determinism. Western avoidance is not explained by culture alone, but it is not encoded as disgust in two genes. In a cooler ecology with fewer harvestable insects, ancient northern Eurasians rarely ate them; over time, variants linked to lower chitinase expression persisted. Culture later built meanings on top of a dietary divide that may already have been thousands of years old.