Traci Watson

Special for USA TODAY

Corrections and clarifications: An earlier headline misstated the type of animals in the experiment. They are monkey-like primates.

Happy hour in the jungle would be happy indeed. Tests show that two monkey-like creatures are fond of alcohol – and the stronger, the better.

Scientists discovered that the aye-aye and the slow loris species both have a taste for booze, a finding that indirectly bolsters one theory for how humans came to appreciate a stiff drink. The aye-ayes in particular were such enthusiastic tipplers that after draining their cups, they searched for more, researchers report in this week’s Royal Society Open Science.

It’s somewhat “shocking” that the animals preferred beverages with the highest alcohol levels, says Matthew Carrigan of Santa Fe College in Gainesville, Fla., who was not involved in the research. Alcohol is loaded with valuable calories, but “it’s a challenge to use those calories without getting inebriated. … If you are climbing around in the trees, 40 to 50 feet off the ground, perhaps at night and surrounded by predators, would you want to be drunk?”

Margaritas are in short supply in the forests of Madagascar, where aye-aye lemurs live. But wild aye-ayes have been seen quaffing nectar, which can ferment into alcohol. The slow loris is a certified drinker, regularly sipping alcohol-laced fermented nectar in its home turf in southeastern Asia.

To test the primates’ palates, researchers recruited a slow loris named Dharma and aye-ayes Morticia and Merlin, all residents of the Duke Lemur Center in Durham, N.C. The scientists presented their subjects with cups of sugar water mixed with different levels of alcohol. The slow loris very slowly lapped the contents of the cups. The aye-ayes stuck their extra-long middle fingers into the cups and licked off the beverage.

The primates, perhaps relying on smell and taste, could tell the higher proof from the weaker, says study co-author Nathaniel Dominy of Dartmouth College via email. Even after they’d polished off the more potent drinks, the aye-ayes repeatedly stuck their fingers into the empty cups, suggesting “a strong attraction,” the scientists write.

The findings intrigue scientists who study the origins of the human affection for alcohol. Chimps, gorillas and humans all carry a gene helps us digest decent amounts of alcohol without drunkenness. Carrigan found that this gene first evolved in an ancestral ape 10 million years ago – long before humans figured out how to make booze.

Why did apes learn to process alcohol before the first cocktail party? Perhaps, researchers have proposed, this trick of metabolism dates to the era when some apes began hanging out on the ground and scooping up lots of fermented fruit beneath the trees.

Aye-ayes also carry the gene for efficient processing of strong drink. So their preference for alcohol supports the idea that the gene helped animals adapt to drinking the stuff, says Penn State’s George Perry, who collaborates with Dominy but was not involved with the current study.

Wild chimps are known to purloin palm wine from jugs and then seem tipsy. But the aye-ayes and loris showed no sign of intoxication, says study co-author and Dartmouth student Samuel Gochman.

Morticia, Merlin and Dharma could not only hold their liquor but also distinguish among “subtle” variations in alcohol content, Dominy says. “I think most humans would have difficulty with this task,” he adds, “but then, we may be relatively desensitized.”