Nope, not oil. Try what is often called the world's second-most valuable commodity*—coffee.
Collectively, we drink four billion cups of coffee a year, enough to fill Yankee Stadium 85 times, according to Jonathan Silvertown's book An Orchard Invisible: A Natural History of Seeds. Silvertown calls coffee beans "the world's most prized seeds," and it makes me smile to consider that in that respect, we're not much different than squirrels or birds, scurrying around in search of seeds to fuel our daily existence.
The appeal of this particular seed for most of us, of course, is caffeine. Sure, I enjoy the taste and aroma of coffee as well, but if I'm honest, that's not my primary motivation—I drink coffee to wake up (or stay awake). It's startling to realize that I'm basically drinking poison, from the coffee plant's perspective:
Caffeine is an all-purpose defensive compound that is poisonous to insects, inhibits the growth of bacteria and fungi, kills slugs and snails," Silvertown writes. But in human brains, caffeine inhibits something else—a substance called adenosine.Humans have been messing with their own brakes for a long time, apparently. A colleague just showed me a paper he found while perusing an online archive. It's from an 1879 edition of The Journal of the Anthropological Institute of Great Britain and Ireland, and has the horrifyingly antiquated title "Ethnological Hints Afforded by the Stimulants in Use Among Savages and Among the Ancients."
Adenosine acts like a brake on the firing of neurons," he explains. "So when caffeine gets in the way of this brake, the human machine speeds up." (And as we learned earlier this year, too much caffeine may drive you crazy.)
The author, a pompous (and blatantly racist) chap named A.W. Buckland, points out that pretty much all civilizations known at that time had "found means of manufacturing some sort of stimulating drink" which often "produce an agreeable exhilaration, and an increase of strength and courage."
Hmm. In other words, coffee is a mark of progress and higher intelligence?
Well, it seems I've already accomplished a lot today.
*This "second-most valuable" detail is frequently published by reputable sources, but as a recent article by Mark Pendergrast points out, this may be erroneous. Coffee is definitely a leading agricultural export in most developing countries, but its ranking depends on what factors you include in calculation. Statistics are rarely simple!