An advanced reading extract with difficult vocabulary highlighted. Original source:

1. OUR TASTE FOR ALCOHOL GOES BACKMILLIONS OF YEARS
Genetics research sheds light on a long human relationship
Alcohol has been partof human existence for millennia. Alcoholic beverages are
an integral part of human culture. Like the wines consumed in Jewish and
Christian rituals, these drinks haveceremonial and religious uses. Until the
nineteenth century, beer, brandy or rumwas the drink of choice for sailors in lieu
of stagnant water during long voyages. Alcoholis a social lubricant, an anesthetic
and an antiseptic. Itis one of the most widely used drugs in the world and has
been manufactured since the advent of agriculture nearly 9000 years ago. How is
it that this drug — an intoxicating poison — has become such a part of human
existence?
A new study finds that our forebears acquired the capacity to digest alcohol some
10 million years ago, among a common ancestor to humans, chimpanzees and
gorillas, and certainly well before we learned to manufactureit. This suggests that
alcohol became partof the human diet much earlier than previously thought, and
in a manner that had significant implications for the survivalof the human
species.
Humans carry with them genetic signatures of their ancestral feeding habits.
Genetic variants that make new food sources available can providetremendous
opportunities to thosewho possess them. The ability to consumemilk, for
example, is due to the “lactase persistence” variant of a gene which emerged
around 7500 years ago among early Europeans. For thoselacking the mutation,
the lactose in milk is a mild poison, eliciting symptoms akinto those of dysentery.
Similarly, the ability to digest alcohol may be a genetic signatureof feeding
pattern among human ancestors: this alcohol tolerance may have made it
possibleto eat over-ripefruit that had fallen to the ground and begun to naturally
ferment. Since few animals can tolerate alcohol, this would have provided our
ancestors with an abundant food sourcefor which there were few competitors. It
may also have contributed to the movetowards a terrestrialrather than arboreal
existence.
The breakdown of alcohol after ingestion is a complex process thatinvolves a
number of different enzymes. Mostof the alcohol that is ingested is broken down
in the gut and liver. This study focused on the enzymeADH4 because it is
abundantin the gut and plays a major role in preventing ingested alcohol from
entering the blood stream. ADH4 fromhuman relatives as distant as the tree

2. shrew weretested for their ability to digest alcohol. The form of ADH4 found in
humans, gorillas and chimpanzees was found to be 40 foldmore efficient at
clearing alcohol than the formfound in moreprimitive species.
ADH4 also digests chemicals that plants produce in order to deter animals from
feeding upon them. However, with the increasein ability to digest alcohol came a
reduced ability to digestmany of these other chemicals. This suggests that the
food containing alcohol was moreimportant. While ADH4 is among the most
important enzymes for the digestion of alcohol, it is not the only one. Another
related enzyme, ADH3, also contributes to the breakdown of
alcohol. Women typically have lower active levels of this enzyme, leading them to
have higher blood levels of alcohol than men after taking a high dose of alcohol.
And ADH4 is not the only enzyme that may have helped humans adapt to the
consumption of alcohol: a variantof a liver enzyme (ADH1B) with high activity in
the breakdown of alcohol emerged among East Asian populations during the
advent of rice cultivation, perhaps as an adaptation to rice fermentation.
Because humans rely upon ADH4 as their primary means to digest alcohol, they
are also susceptibleto hangovers. ADH4 and similar enzymes digest alcohol by
converting it into another chemical, acetaldehyde, which causes the skin flushing,
headache and other symptoms of overindulgence. Themodern consumption of
alcohol has been characterized as an "evolutionary hangover," an adaptation to
modest levels of alcohol in food sources which left humans proneto alcohol
abuseonce we learned how to manufactureit in highly concentrated forms. And,
in fact, genetic variants of ADH4 have been linked to alcohol and
drug dependence, although there are many other genes that may influence
susceptibility to alcohol dependency. Regardless of the role ADH4 plays in alcohol
addiction, it’s clear that our complex relationship with alcohol dates back millions
of year, and began, in fact, before we wereeven human.
http://www.scientificamerican.com/article/our-taste-for-alcohol-goes-back-
millions-of-years/