Matthew Carrigan at Santa Fe College in Gainesville, Florida, and his co-workers have discovered that ancient apes were able to metabolise ethanol. They acquired this ability around 10 million years ago, which coincides with when they came down from the trees onto the forest floor.
They were analysing the gene encoding the enzyme ADH4, which is made in the digestive tract to establish ethanol, and tracing its 70 million year evolutionary history. This was achieved by studying the gene in 28 mammals (including 17 primates), and synthesising ancestral forms of the enzyme. They found that ADH4 from ancestors of humans, gorillas and chimpanzees was much more efficient at breaking down ethanol than the enzyme found in more ancient gorillas.
It has been proposed that this change was due to the availability of fermented fruit on the forest floor than in trees, and helped the hominids adapt to life in their new environment.