Why Europeans can't stomach silkworm soup: the answer lies in 9,000-year-old genes

Edible insects have drawn growing attention as a potential solution to future food shortages, yet the industry has struggled to gain a foothold in Europe in particular. A new study suggests that Europeans' deep-seated aversion to eating insects may not stem from cultural bias or modern hygiene norms — but from genes shaped thousands of years ago.

According to volume 12, issue 23 of the international journal Science Advances, Europeans were already consuming almost no insects at the genetic level as far back as roughly 9,000 years ago, during the Neolithic farming era — long before medieval religion took hold or contemporary notions of hygiene emerged.

A research team led by Manuel Piñero and Pablo Librado at the Institute of Evolutionary Biology (IBE) in Barcelona, Spain, analyzed insect consumption among ancient Europeans at the genomic level.

Dental calculus as a record of ancient diets

To determine what ancient people actually ate, the research team analyzed dental calculus — one of the most powerful biological archives available. Even after thousands of years, calculus preserves microscopic food residues and DNA from the time of consumption, making it an invaluable tool for reconstructing ancient diets.

The team assembled a large dataset to enable thorough genetic comparisons. They examined dental calculus from 745 modern humans and 18 Neanderthals, and included samples from 57 chimpanzees and 39 gorillas as reference points. They then cross-referenced each sample against a database of mitochondrial genomes from 10,761 insect species worldwide, systematically searching for traces of insect DNA.

Results of insect DNA analysis detected in dental calculus from great apes and humans. On the horizontal axis, samples are arranged from left to right in order of decreasing average insect DNA detected — meaning those on the right consumed fewer insects. [Science Advances, Vol. 12, No. 23]

The results revealed stark differences. Gorillas showed by far the highest levels of insect DNA — a finding attributed to their habit of consuming large quantities of leaves, which likely caused them to inadvertently swallow beetles and other insects clinging to the foliage.

Ancient Europeans, by contrast, showed only trace amounts of insect DNA in their dental calculus — comparable to levels found in chimpanzees living in tropical rainforests, where insects make up less than 4 percent of the diet despite an abundance of surrounding fruit and leaves. The implication is that ancient Europeans were not deliberately eating insects at all.

Even the minuscule quantities of insect species detected turned out, on closer inspection, to be the result of accidental ingestion or post-mortem contamination.

A sample from the Czech Republic dating back 29,500 years contained DNA from midge larvae typical of lake sediments, most likely swallowed while drinking water.

Samples from Germany dating to 9,200 years ago and from Egyptian mummies yielded DNA from booklice commonly found in grain stores — almost certainly ingested unintentionally through contaminated food supplies.

The research team concluded that the vast majority of insect DNA found in European dental calculus reflected either accidental consumption or post-mortem contamination from soil insects in burial sites.

Insect-digesting ability weakens with distance from the equator

Geographic distribution of modern and ancient samples used in the study. Circles (●) represent modern human populations; diamonds (◆) represent ancient samples. Larger diamond markers indicate a greater number of samples, and color indicates average age. The horizontal dashed line across the middle of the map (8 degrees north latitude) marks the threshold for regions where insect consumption is most prevalent among humans. [Science Advances, Vol. 12, No. 23]

To strengthen their findings, the research team mapped digestive enzyme genes in 2,396 modern humans. The driver of genetic variation turned out to be simpler and more clear-cut than expected. Factors that might intuitively seem relevant — climate, temperature, even the proportion of arable land — explained none of the variation in gene distribution.

The only statistically significant predictor was distance from the equator, defined as 8 degrees north latitude. The correlation ranked in the top 0.04 to 0.53 percent of all genetic variation observed — a result highly unlikely to be due to chance.

People living closer to the equatorial tropics had significantly stronger versions of the genes responsible for breaking down chitin, the tough outer shell of insects. In higher-latitude regions such as Europe, that digestive capacity had weakened considerably.

The roots of this genetic divide run deep in human history. Analysis of 1,663 ancient human genomes confirmed that the latitude-based gap in these genes already existed roughly 9,000 years ago, at the dawn of Neolithic agriculture.

A product of evolution, not culture

The research team's central argument is that Europeans' aversion to insects is not a matter of cultural prejudice or finicky taste, but the product of thousands of years of evolution.

Europe's cooler climate supports far fewer insects — both in density and species diversity — than tropical regions. Eating insects only makes caloric sense when large quantities can be gathered easily in one go; in the European environment, foraging for insects would have cost more energy than it returned.

Ultimately, ancient Europeans had no need to rely on insects for sustenance. As a result, they faced no evolutionary pressure to maintain the ability to digest chitin, and that capacity gradually faded.

The research team suggested that successfully introducing edible insects into European markets would require either processing them into an unrecognizable powder form or developing manufacturing techniques that remove indigestible components before the product reaches consumers.

Meanwhile, according to the UN Food and Agriculture Organization (FAO), 1,611 insect species worldwide are registered as edible for human consumption.

Reference

DOI: 10.1126/sciadv.aec6939

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