"Scrumping" is the name coined in a paper led by researchers at Dartmouth and the University of St Andrews in Scotland for the fondness apes have for eating ripe fruit from the forest floor. These primates' palate for picked-up produce has taken on new importance in recent years, the researchers report in the journal BioScience.

But scientists cannot fully understand the significance of this behavior -- particularly for human evolution -- because "we never bothered to differentiate fruits in trees from fruits on the ground," says Nathaniel Dominy, the Charles Hansen Professor of Anthropology at Dartmouth and a corresponding author of the paper, which includes co-author Luke Fannin, a postdoctoral researcher at Dartmouth.

In other words, scrumping by no name at all just looks like eating fruit, Dominy says. The researchers write that geneticists reported in a 2015 study that eating fermented fruit may have triggered a single amino acid change in the last common ancestor of humans and African apes that boosted their ability to metabolize alcohol by 40 times.

"It's a fascinating idea, but nobody studying these ape species, or Asian apes, had the data to test it. It just wasn't on our radar," Dominy says. "It's not that primatologists have never seen scrumping -- they observe it pretty regularly. But the absence of a word for it has disguised its importance. We're hoping to fill an important void in scientific discourse."

Scrumping, the researchers write, describes the act of gathering -- or sometimes stealing -- windfallen apples and other fruits. The word is the English form of the medieval German word "schrimpen," a noun meaning "shriveled" or "shrunken" used to describe overripe or fermented fruit. In England today, scrumpy refers to a cloudy apple cider with an alcohol by volume content that ranges from 6 to 9%.

The researchers set out to better determine how common their new behavior classification is among great apes. They examined dietary reports of orangutans, chimpanzees, and mountain and western gorillas observed in the wild.

Feeding events were cross-referenced with how high off the ground the animal was when it ate, as well as the height at which the fruit grows. If an ape at ground level was recorded eating a fruit known to grow in the middle or upper levels of the forest canopy, it was counted as scrumping.

The researchers found that African apes "scrump" on a regular basis, but orangutans do not. These results corroborate the 2015 gene-sequencing study, which found the primary enzyme for metabolizing ethanol is relatively inefficient in orangutans and other non-human primates.

The authors of the BioScience paper propose that metabolizing ethanol may let African apes safely eat the ripe, fermented fruit they find on the ground. This adaptation could free them from competing with monkeys for unripe fruit in trees. It also could spare large apes the risk of climbing and possibly falling out of trees, which a 2023 study by Dominy and Fannin reports is so incredibly dangerous that it influenced human physiology.

Given that chimpanzees consume about 10 pounds of fruit each day, the team's analysis suggests these animals ingest a non-trivial amount of alcohol, Dominy says. That level of intake suggests that chronic low-level exposure to ethanol may be a significant component of chimpanzee life, and a major force of human evolution.

The next step is measuring levels of fermentation in fruits in the trees versus fruits on the ground to better estimate alcohol consumption in chimpanzees, Dominy says.

"Scrumping by the last common ancestor of gorillas, chimpanzees, and humans about 10 million years ago could explain why humans are so astoundingly good at digesting alcohol," Dominy says. "We evolved to metabolize alcohol long before we ever figured out how to make it, and making it was one of the major drivers of the Neolithic Revolution that turned us from hunter-gatherers into farmers and changed the world."

Humans might also have retained social aspects that apes bring to scrumping, says Catherine Hobaiter, a professor of psychology and neuroscience at St Andrews and co-corresponding author of the study.

"A fundamental feature of our relationship with alcohol is our tendency to drink together, whether a pint with friends or a large social feast," Hobaiter says. "The next step is to investigate how shared feeding on fermented fruits might also influence social relationships in other apes."

The word scrumping will catch on if other scientists see its descriptive value, Dominy says. The paper in BioScience notes other words invented to capture new concepts, such as "symbiosis" -- coined in 1877 -- and the now ubiquitous "meme," introduced by evolutionary biologist Richard Dawkins in 1976.

"These are great examples of words that we never knew we needed, until we did. If the term is useful, then it will catch on," Dominy says. "That's natural selection at work!"

Yet, teeth without staining may not mean that people didn't chew betel nuts. Now, using a new method, an international team of researchers examined ancient dental plaque from Bronze Age Thailand and found evidence of betel nut chewing.

"We identified plant derivatives in dental calculus from a 4,000-year-old burial at Nong Ratchawat, Thailand," said first author of the Frontiers in Environmental Archaeology study Dr Piyawit Moonkham, an anthropological archaeologist at Chiang Mai University in Thailand. "This is the earliest direct biomolecular evidence of betel nut use in south-east Asia."

"We demonstrate that dental calculus can preserve chemical signatures of psychoactive plant use for millennia, even when conventional archaeological evidence is completely absent," added Dr Shannon Tushingham, the senior author, who is the associate curator of anthropology at the California Academy of Sciences. "In essence, we've developed a way to make the invisible visible -- revealing behaviors and practices that have been lost to time for 4,000 years."

Hidden in plaque

At Nong Ratchawat, an archaeological site in central Thailand that dates back to the Bronze Age, 156 human burials have been unearthed since 2003. For the present study, the team collected 36 dental calculus samples from six individuals.

Back in the lab, they removed tiny amounts of plaque from the samples and the chemical residues found therein underwent analysis. The team also used betel liquid samples they produced themselves to ensure psychoactive compounds could be reliably detected through their analysis and to understand the complex biochemical interactions between ingredients. "We used dried betel nut, pink limestone paste, Piper betel leaves, and sometimes Senegalia catechu bark and tobacco. We ground the ingredients with human saliva to replicate authentic chewing conditions," Moonkham said. "Sourcing materials and experimentally 'chewing' betel nuts to create authentic quid samples was both a fun and interesting process."

The results showed that three of the archaeological samples - all stemming from a molar of the same individual, Burial 11 - contained traces of arecoline and arecaidine. These organic compounds, found in betel nuts but also plants like coffee, tea, and tobacco, have pronounced physiological effects on humans. This suggests that betel nuts were chewed as early as 4,000 years ago in Thailand.

'Archaeologically invisible' proof

"The presence of betel nut compounds in dental calculus does suggest repeated consumption, as these residues become incorporated into mineralized plaque deposits over time through regular exposure," explained Tushingham. Accordingly, the absence of tooth-staining raises questions. It could be the result of different consumption methods, the team pointed out. It could also be due to post-consumption teeth cleaning practices, or post-mortem processes affecting stain preservation over 4,000 years.

While traces of betel nut chewing were found in samples from only one individual, there is currently no proof that Burial 11 received special treatment or was of elevated social status or unique ritual significance compared to the other burials at Nong Ratchawat. The presence of stone beads as grave goods, however, could provide hints as to the individual's identity or lived experience. Studying more individuals at Nong Ratchawat and other local sites to learn when and to whom such grave goods were given could provide valuable evidence, the team said.

The methods the researchers applied can be used to examine the remaining burials at Nong Ratchawat and at other sites, they said. "Dental calculus analysis can reveal behaviors that leave no traditional archaeological traces, potentially revolutionizing our understanding of ancient lifeways and human-plant relationships," Tushingham said. "It could open new windows into the deep history of human cultural practices."

"Understanding the cultural context of traditional plant use is a larger theme we want to amplify -- psychoactive, medicinal, and ceremonial plants are often dismissed as drugs, but they represent millennia of cultural knowledge, spiritual practice, and community identity," Moonkham concluded. "Archaeological evidence can inform contemporary discussions by honoring the deep cultural heritage behind these practices."