Hunger can motivate you to do so many things: Break your diet and eat those large cajun-style fries from Five Guys; go to that pretentious college art exhibit because it has free food; elbow a co-worker out of line in the cafeteria when you see there's just one grilled cheese left.

But hunger doesn’t just determine whether you’ll be eating a salad or a Reuben sandwich; Ruth DeFries argues that it's the driving force behind human civilization.

“Every species, from the smallest to the largest, has one big challenge: that’s to find enough food; to feed themselves, to reproduce, and to feed their offspring. To me, that’s the fundamental aspect of civilization, to be able to produce enough food to feed everyone. Without that, we have no civilization," explains DeFries, a professor of sustainable development at Columbia University and author of The Big Ratchet: How Humanity Thrives in the Face of Natural Crises.

That quest for food has led us dominate most of the planet. The next time you’re on an airplane, just look out the window, you’ll see artifacts and signs of our presence everywhere. According to DeFries, “about half of the world is devoted, in one way or another, [to growing the food to] feed us.”

The desire for more and more food has shaped the history of our species in surprising ways. Consider South American guano (bird droppings). No, really, consider it. After explorer and naturalist Alexander von Humboldt discovered that it made extraordinarily good fertilizer in the early 19th century, it transformed European agriculture, making fields much more productive. There were guano mines, ships to carry it across the ocean... guano became big business.

DeFries believes our hunger for food is a big part of the reason we explore, discover, and invent. Extracting nitrogen from the air, animal husbandry, the domestication of crops, and yes, using South American guano, are all part of that.

This food-fueled innovation can also lead to tragedy, as the Irish potato famine demonstrated. The potato, native to the Americas, was introduced to Europe in the late 1500s. It eventually became a staple of peasant diets throughout Europe, especially in Ireland — but it had a fatal flaw. Potatoes, being genetic clones of each other, are especially susceptible to blight, so when a blight did ravage Ireland’s potatoes, it led to a huge, deady famine.

Today, technological advances in fertilizer, irrigation, and genetics mean we’re producing more food per person than we ever have before, explains DeFries. But we also see the downsides of technological developments in food and agriculture, with species losing their habitats due to the need for agricultural space, fertilizer runoff eroding water quality, and our desire for meat being a primary cause of climate change.

DeFries sees this as all as part of a cycle.

“When we apply our ingenuity, it creates some kind of problem, and then we use our ingenuity again to come up with some solution, with then again creates some kind of problem. So it’s this existential way that our civilization goes forward...and I think that’s the way we’ll always be.”