Insects in Chang Moi, Mueang Chiang Mai District, Chiang Mai, Thailand.
Credit: mohigan. Licence: CC BY-SA 3.0, via Wikimedia Commons.
Humans are strange creatures. While we recoil at the thought of tucking into a dish of sautéed maggots, fried grasshoppers or other insects, we happily eat their close arthropod relatives, crabs, lobsters and prawns, and yet the evidence is that this has only been so for Northern Eurasians for about the last 9,000 year.
People are also strange in another way: despite all the evidence to the contrary and with no supporting evidence at all, there are people who believe the whole of history can be compressed into a few thousand years and that animals can be created by magic without ancestors.
For biblical literalists, every human who has ever lived must be squeezed into the few thousand years since the supposed creation of the first couple. Yet evidence preserved in something as commonplace as calcified plaque on ancient teeth tells a very different story: one of several human lineages, changing diets, inherited genetic variation and adaptation to contrasting environments over tens of thousands of years.
In a paper published in Science Advances, Manuel Piñero and Pablo Librado of the Institute of Evolutionary Biology in Barcelona combined two independent sources of evidence to investigate the history of human insect-eating, or entomophagy. They searched ancient dental calculus for insect DNA and examined genetic variants affecting our ability to digest chitin—the tough polysaccharide forming much of an insect’s exoskeleton.
The researchers screened dental calculus from 745 prehistoric Homo sapiens, including individuals who lived as long as 33,000 years ago, together with samples from Neanderthals and other primates. The wider analysis reconstructed aspects of insect consumption from about 9,000 to more than 102,000 years ago—all comfortably before the date on which young-Earth creationists claim the Universe and everything in it was created.
Insect DNA was scarce in the calculus of northern Eurasian Homo sapiens, and the insects detected were generally consistent with accidental ingestion in food or water rather than regular, deliberate consumption. Neanderthal calculus, however, contained substantially more insect DNA, at levels comparable with those found in western chimpanzees. Much of it came from flies and mosquitoes, potentially supporting the suggestion that Neanderthals sometimes ate fly larvae associated with stored or scavenged animal carcasses. This remains an inference rather than proof of a particular food-processing practice, but it is testable evidence drawn from the material remains of real populations—not speculation based on ancient folklore.
The second line of evidence came from the genes CHIA and CTBS, which encode the stomach-expressed enzymes acidic chitinase and chitobiase. Genetic variants associated with higher expression of these enzymes are more frequent near the tropics, where insects are abundant throughout the year and remain part of many traditional diets. Variants associated with lower chitinase expression predominate at higher northern latitudes. Ancient genomes show that this geographical pattern was already present at the beginning of agriculture, some 9,000 years ago, and persisted despite subsequent large-scale population movements. Neanderthals—and the single Denisovan examined—carried variants associated with greater capacity to digest chitin.
The results do not show that every fragment of insect DNA represents a deliberately eaten insect, nor do they establish that modern Europeans inherited their dietary habits from Neanderthals. What they reveal is subtler and more informative: different human populations and lineages carried different genetic capacities and exploited different food resources as they lived in different ecological circumstances. Diet, geography, inherited variation and population history all left detectable signatures in both their genomes and their teeth.
This is evolution written simultaneously in ancient DNA, digestive physiology and prehistoric dental calculus. The findings make sense within the scientific account of human origins, in which related human lineages diverged, adapted and sometimes coexisted during a history extending hundreds of thousands of years. They make no sense within Genesis, which knows nothing of Neanderthals, Denisovans, inherited genetic clines or human populations living more than 100,000 years ago. Once again, the evidence does not merely fail to support the biblical account; it describes a history that the biblical authors could not have imagined.
Chitinase Genes^ Genomic Fossils of an Insect-eating Past. Chitin is the tough structural carbohydrate found in insect exoskeletons and the cell walls of fungi. Although mammals do not manufacture chitin, many produce enzymes called chitinases that can break it down, including elephants, rhinoceroses, okapis and manatees.The study in Science Advances was accompanied by a news release from the Institute of Evolutionary Biology:
This otherwise curious ability is an inheritance from our distant evolutionary past.
In a Science Advances study published in 2018, researchers compared the genomes of 107 placental mammals. They reconstructed the common ancestor of living placental mammals as possessing five functional copies of acidic mammalian chitinase genes, known collectively as CHIAs.
This is consistent with fossil evidence that early placental mammals were generally small insect-eaters. Insects were an abundant source of food while non-avian dinosaurs dominated many of the larger terrestrial ecological niches.
What happened after the dinosaurs?
Following the end-Cretaceous mass extinction about 66 million years ago, placental mammals diversified into ecological niches previously occupied by dinosaurs and other extinct animals. Some lineages remained insectivorous, while others evolved herbivorous, carnivorous or omnivorous diets.
As insects became less important in a lineage’s diet, maintaining several fully functional chitinase genes no longer provided the same advantage. Mutations that disabled redundant copies were therefore less likely to be removed by natural selection. Over time, some genes were deleted while others deteriorated into non-functional pseudogenes.
The study found a positive relationship between the proportion of invertebrates in a modern mammal’s diet and the number of functional CHIA genes it retained. The aardvark, for example, still possesses five functional copies, while the independently evolved insect-eating tamandua retains four. Many predominantly non-insectivorous mammals have lost several.
The evidence inside the human genome
Humans retain a functional CHIA gene but also carry non-functional remnants of ancestral chitinase genes. These pseudogenes are genomic fossils: inherited fragments recording the insect-eating ancestry of early placental mammals.
The surviving enzyme may perform more than one function. Besides contributing to chitin digestion, acidic mammalian chitinase is expressed in the respiratory system and may help defend against fungi, parasites and other sources of inhaled or ingested chitin. A gene originally retained because it was useful in obtaining food can therefore persist because it also performs other useful functions.
The geographical differences in chitinase expression identified in the newer study represent more recent modification of this much older inherited system. Tropical human populations, Neanderthals and the Denisovan examined retained variants associated with greater chitin-digesting capacity, while northern Eurasian Homo sapiens carried variants associated with reduced expression.
This is not the pattern expected if every species had been separately created with a purpose-built genome. It is the pattern predicted by evolution: shared ancestral genes, modification according to changing ecological pressures, repeated loss of functions that are no longer important, and damaged genetic remnants inherited by descendants millions of years later.
European Homo sapiens ate fewer insects than Neanderthals and tropical populations
A study by the IBE (CSIC-UPF) analyses genetic traces of insects in dental calculus and reveals that insect consumption was rare among prehistoric Europeans, while it may have been more common among Neanderthals. Insects would only have been a regular part of the diet among humans living in tropical latitudes, who retained a genetic adaptation that made them easier to digest.
A study by the Institute of Evolutionary Biology (IBE), a joint centre of the Spanish National Research Council (CSIC) and Pompeu Fabra University (UPF), uses genomic analyses to reconstruct insect consumption from 9,000 to more than 102,000 years ago. Published in Science Advances, the research suggests that insect consumption was sporadic and incidental in Europe, Central Asia and East Asia, while it may have been more common in tropical regions and, above all, among Neanderthal populations. The findings shed light on human evolution, ecology and present-day insect consumption.
Anatomically modern humans, or Homo sapiens, arrived in Europe at least 46,000 years ago. To look for evidence of insect consumption, the IBE team analysed 745 samples of dental calculus from individuals dating back up to 33,000 years. Dental calculus preserves traces of DNA from species regularly consumed as part of the diet.
The dental analyses suggest that modern humans in northern Eurasia did not practise entomophagy on a regular basis.
In addition, the insect species identified in the dental calculus of Homo sapiens point to incidental ingestion, through the consumption of water or contaminated food.
The team also studied human genes involved in the digestion of chitin, a complex carbohydrate — or polysaccharide — that makes up the exoskeleton of insects. In human populations from northern Eurasia, chitinase genes — which produce an enzyme found in the stomach that breaks down chitin — carry mutations associated with a reduced ability to digest insect exoskeletons.
This trait has persisted for the past 9,000 years, since the arrival of agriculture.
The scarce presence of insects in the diet of northern Eurasian populations suggests that the absence of entomophagy is not only due to recent cultural factors, but also reflects a long ecological and evolutionary history.
Pablo Librado, senior author
Institut de Biologia Evolutiva (CSIC–Universitat Pompeu Fabra)
Barcelona, Spain.
Insects in the Neanderthal diet
Neanderthals inhabited Eurasia from around 400,000 years ago until their disappearance approximately 40,000 years ago. Despite occupying the same environment as Homo sapiens and coexisting with them for a brief period, the analysis of 18 Neanderthal dental calculus samples showed a greater presence of insect DNA than that found in anatomically modern humans. This abundance in Neanderthals was comparable to that observed in western chimpanzees, which use entomophagy as a dietary supplement in the savannah, especially during periods of drought. By comparison, gorillas were the study group with the highest presence of insect DNA in their dental calculus, due to the incidental ingestion of numerous insects associated with the foliage that forms part of their diet.
The most abundant DNA remains in Neanderthal dental calculus correspond to dipterans, the group of insects that includes flies and mosquitoes, with mosquitoes being particularly prominent. The results support a recent hypothesis suggesting the regular consumption of animal carcasses infested with fly larvae.
Domestic honeybee (Apis mellifera).
Bees are among the insects traditionally domesticated in various human cultures.Credit: Juan Manuel Calvo Martin.
The abundance of mosquito remains reinforces the possibility that the carcasses of their prey remained in ponds and marshy areas, ideal environments for insects to lay their eggs.
Pablo Librado.
The study also revealed that Neanderthals carried variants of the chitinase gene that facilitated insect digestion. This trait was also identified in the only Denisovan specimen analysed, belonging to an archaic human lineage first identified in Denisova Cave, Siberia.
The genetic footprint of entomophagy in the tropics
The team analysed genes linked to the digestion of chitin from insect exoskeletons. These genes are responsible for producing in the stomach the chemical “scissors” that break down chitin: the enzymes acidic chitinase and chitobiase. In both ancient and present-day samples, the study identified genetic variants associated with higher expression of these enzymes in populations living near the tropics.
Large quantities of insects need to be consumed to compensate for the high caloric cost involved in collecting them. In the tropics, social insects such as termites and ants are more readily available: their biomass and diversity allow for sustainable exploitation throughout the year, while also contributing to pest control.
Manuel Piñero, first author.
Institut de Biologia Evolutiva (CSIC–Universitat Pompeu Fabra)
Barcelona, Spain.
Expression of these enzymes gradually decreases as populations move towards higher latitudes. This latitudinal genetic variation, maintained for at least 9,000 years, reflects the abandonment of entomophagy in European populations.
The future of entomophagy in Europe
Human population growth, together with the climate crisis, environmental pressure and current patterns of production and consumption, has driven the search for alternative food sources in recent years. With 1,611 insect species catalogued as edible, organisations such as the Food and Agriculture Organization of the United Nations (FAO) have proposed insects as a sustainable food source.
However, despite the fact that hundreds of millions of people already consume them, Western societies continue to show an aversion to entomophagy. Although this rejection may have a cultural basis, its origin remains unknown.
Manuel Piñero, predoctoral researcher in the Ancient Population Genomics group at the IBE, displays live beetles (Tenebrio molitor) and preserved specimens from the Museu de Ciències Naturals de Barcelona, used in the group’s research.Beyond cultural or religious factors, our results suggest that the low availability of insects outside the tropics may have been a key factor in the abandonment of entomophagy, leading to a reduced ability to digest insect exoskeletons.
Pablo Librado.
Today, however, industrial processing makes it possible to harness their nutritional properties without the need to digest this component, while also enabling large-scale production on edible-insect farms.
The Ancient Population Genomics research group, led by Pablo Librado at the IBE, studies the process of domestication, mainly using insects as model species. To do so, the researchers compare the genomes of insect species recently approved for human consumption with those of specimens obtained from entomological collections.
We study the evolution of domestication in animals, which can also provide insights to improve the exploitation of insects for consumption, both as livestock feed and as food for humans.
Pablo Librado.
Publication:
What makes this study especially persuasive is the convergence of two independent lines of evidence. Insect DNA preserved in dental calculus records what ancient individuals encountered or consumed, while variation in the genes responsible for digesting chitin reveals the longer evolutionary history of their populations. Neither source alone can reconstruct every meal, but together they show consistent differences between northern Eurasian Homo sapiens, Neanderthals and tropical human populations.
Those differences were not imposed upon separately created and genetically fixed “kinds”. They arose within related mammalian and human lineages carrying an inherited digestive system whose origins extend back to the insect-eating ancestors of placental mammals. As diets and environments changed, natural selection preserved useful functions, reduced others and permitted redundant gene copies to decay into pseudogenes. The result is the untidy mixture of functioning genes, altered expression and disabled remnants expected from descent with modification—not from intelligent design.
The chronology is equally unhelpful to creationism. The evidence encompasses modern humans living tens of thousands of years ago, Neanderthals whose history stretches back hundreds of thousands of years, and chitinase genes inherited from mammalian ancestors living before the extinction of the non-avian dinosaurs 66 million years ago. Every stage lies outside the cramped few-thousand-year chronology demanded by a literal reading of Genesis.
Once again, evolutionary theory was not an incidental gloss added after the research had been completed; it supplied the framework that made the evidence intelligible. Common ancestry explains why humans and other placental mammals share chitinase genes, ecological adaptation explains their differing activity, and relaxed selection explains the pseudogenes left behind. Genesis explains none of it. The real history remains written in our teeth and genomes, whether creationists choose to read it or not.
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