There, chimpanzees of two different subspecies—the eastern (Pan troglodytes schweinfurthii) and the western (P. t. verus)—eat about 4.5 kilograms of fruit per day, with an average ethanol content of 0.31% to 0.32%. The result: an intake of between 13 and 15 grams of alcohol per day, which for both male and female chimpanzees is comparable to two or three beers for a human. The natural fermentation of ripe fruit, the theory goes, exposed hominids to small doses of ethanol for millions of years. Researchers analyzed more than 500 fruit samples from 20 plant species in the rainforests of Uganda and the Ivory Coast. According to Dudley, the lack of any obvious change in chimpanzees’ behavior is due to a simple fact: they always consume alcohol with fruit.