Possibly the most iconic is the story of African elephants and marula fruit. According to this popular wisdom, elephants across Africa preferentially serve on the fallen, ripening, fermenting fruit of the marula tree becoming drunk. Such stories have been scrutinized, however. Researchers have hinted that anecdotes of inebriated elephants may be a result of ‘subjectifying elephant behavior.’ However, the debate is based on considerations mapping on human ethanol metabolism, which may be a crucial error. Humans have a tremendous evolutionary link with ethanol, pre-dating anthropogenic roots, and hold surprisingly effective ethanol metabolism, by a mutation that evolved in our last common ancestor with African great apes.
Study Name:Genetic evidence of widespread variation in ethanol metabolism among mammals: revisiting the ‘myth' of natural intoxication
Humans have a long evolutionary relationship with ethanol, pre-dating anthropogenic sources, and possess unusually efficient ethanol metabolism, through a mutation that evolved in our last common ancestor with African great apes. Increased exposure to dietary ethanol through fermenting fruits and nectars is hypothesized to have selected for this in our lineage. Yet, other mammals have frugivorous and nectarivorous diets, raising the possibility of natural ethanol exposure and adaptation in other taxa. We conduct a comparative genetic analysis of alcohol dehydrogenase class IV (ADH IV) across mammals to provide insight into their evolutionary history with ethanol. We find genetic variation and multiple pseudogenization events in ADH IV, indicating the ability to metabolize ethanol is variable. We suggest that ADH enzymes are evolutionarily plastic and show promise for revealing dietary adaptation. We further highlight the derived condition of humans and draw attention to problems with modeling the physiological responses of other mammals on them, a practice that has led to potentially erroneous conclusions about the likelihood of natural intoxication in wild animals. It is a fallacy to assume that other animals share our metabolic adaptations, rather than taking into consideration each species’ unique physiology.