Why elephants don't get drunk on fruit like humans

Over many generations, consistent consumption of certain foods has led to genetic changes that allow organisms to process those foods more efficiently without causing harm to their bodies.

In 85 mammal species, the ADH7 gene has become nonfunctional at least 10 separate times during evolution, meaning these species no longer use this gene to break down ethanol. This loss occurred in groups like elephants, whales, and cows, likely because their diets contained little alcohol, reducing the need to maintain this metabolic function.

In herbivorous mammals like elephants and horses, the ADH7 gene has been lost over evolutionary time, and this loss is linked to diets that contain little fruit or nectar. The pattern is not just about eating less fruit, but about a general shift to eating more plant material, which may have reduced the need for genes that process ethanol.

In mammals that eat a lot of fruit or nectar, genetic pressure to maintain a functional version of the ADH7 gene is stronger, likely because ethanol in these foods requires efficient metabolism. In mammals without such diets, this genetic pressure is weaker.

Humans have a unique genetic variation in the ADH7 enzyme that affects how they break down alcohol, and most other mammals do not have this variation. Because of this, using human alcohol metabolism to predict how other animals process alcohol leads to incorrect conclusions about their intoxication risk.