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...
Mechanism
Synthesis from 1 study
When animals stopped eating ripe fruit and nectar and started eating mostly leaves and grass, they no longer needed a gene that breaks down alcohol from fermented food. Without that need, the gene slowly broke down over generations. Bacteria in their guts also helped clean up other plant chemicals,...
Most probable mechanism
When animals eat mostly leaves and grass instead of ripe fruit or nectar, they stop getting much alcohol from their food. Without needing to break down that alcohol, the gene that makes the enzyme to do it isn't kept by evolution anymore, so it breaks down over generations. In some cases, bacteria in the gut take over cleaning up other plant toxins, so the body doesn't need that gene at all.
Diet shifts from ethanol-rich plant materials like fermenting fruits and nectars to low-ethanol plant materials such as leaves, grasses, and stems.
Ethanol is no longer regularly ingested in significant amounts, removing the selective advantage of efficient ethanol metabolism.
The enzyme alcohol dehydrogenase IV, encoded by the ADH7 gene, is no longer needed for detoxifying ethanol in the upper gastrointestinal tract.
Loss-of-function mutations in the ADH7 gene, such as premature stop codons and frameshifts, accumulate without being removed by natural selection.
The ADH7 gene becomes pseudogenized, resulting in complete loss of functional enzyme production.
Toxic plant alcohols from leaves and stems are metabolized by microbial communities in the hindgut or foregut, providing functional redundancy that further reduces selective pressure to maintain ADH7.
Evidence from Studies
Supporting (1)
Community contributions welcome
Genetic evidence of widespread variation in ethanol metabolism among mammals: revisiting the ‘myth' of natural intoxication
Contradicting (0)
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