Dominy, an anthropologist and evolutionary biologist at Dartmouth, said that in nature, "some of the highest (alcohol) recordings from a wild plant come from overripe palm fruits in Panama. The levels were about 6 percent."
The researchers found that primates could detect varying concentrations of alcohol, and that they adjusted their intake of the nectar with the highest amounts. Morticia and Merlin even continued to probe the containers with the greatest amounts of alcohol long after they were emptied, implying they wanted more.
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"The prevailing assumption is that alcohol is toxic, negatively affecting motor control, survival, and fitness," Gochman said. "However, calories are scarce in the environment, and alcohol is a rich source of calories for primates with high metabolisms, so there may be nutritional benefits to consuming moderate amounts of alcohol that outweigh the costs, especially if a species has evolved a digestive system that can break it down hyper-efficiently, as ours does."
It could even be that fermentation evolved, like fragrance, to attract consumers to slightly boozy edibles. Dominy explained that if consuming more nectar or fruit benefits the plant, such as via better pollination and seed dispersal, then fermentation could bring mutual benefits to the plant and consumer.
Nocturnal primates may be particularly good at finding fermented foods and liquids, since they rely on smell to find food at night. Dominy says that "alcohols are lightweight molecules that can travel far from their source, so it is possible that nocturnal primates can better detect and navigate towards fruits or nectars on the basis of smell."
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The behavior could be extra advantageous for these night-loving primates, he said, since they have high metabolic demands and must fuel their bodies with calories, which alcohol is a rich source of in the wild.
Still, day-active (diurnal) primates must eat a fair amount of natural alcohol too, since all fruit contains at least trace amounts of alcohol. Primates like gibbons have a diet that is up to 95 percent fruit, and given the commonness of fermented fruits, a gibbon's regular alcohol intake could be fairly significant.