At least, not tame yeast.

That's the gospel according to Ed Wood, a retired pathologist and sourdough bread expert. I called on Wood because I wanted to know where sourdough came from. Bear with me, because I'm about to sound a wee bit stupid, or at least baking-impaired.

Pictured: Sourdough starter I had absolutely nothing to do with. (My DIY is pasted on, yay!) This image comes from Flickr user fooey, and shows starter on day six of a 14-day process. It's under CC.

I have seen people make sourdough–specifically, Amish Friendship Bread–by snipping off a bit of fermented "starter" dough and mixing it with flour and water. But it occurred to me last winter, while flipping through an old TIME/LIFE illustrated book on the cuisine of the American Northwest, that I had no earthly idea where the starter came from. ("Little plastic baggies handed out by old ladies at church" being an obvious, but not very satisfying, answer.)

Real sourdough, Wood tells me, begins with nothing but flour, water and your friendly, native microscopic flora and fauna. Set out a mixture of wet flour, and wild yeasts and bacteria will drop in to munch on it. The yeast produce fermentation and make the bread rise by consuming sugars in the flour and breaking them down into water, alcohol and carbon dioxide gas. The bacteria also eat sugars, leaving behind acids that give sourdough its tangy taste. There are starter recipes out there that call for store-bought yeast, but Wood brushes them off as flavorless junk. San Francisco's Exploratorium science museum has a more objective explanation. They say wild works best because yeast and bacteria are balanced. Purchase your yeast, and any wild bacteria will end up hopelessly outnumbered, unable to compete with yeast for sugary sustenance. No bacteria, no flavor.

I'm a pessimist by nature, especially when it comes to baking, so I had to ask: With all the wild bacteria and yeast out there, do you always get the right ones?

"Oh, no," Wood told me. "You have to be a little bit lucky to get a good wild yeast that will leaven the bread and a good bacteria for flavor. You don't always end up with something worth making bread out of."

How do you get it right? Trial and error. "Bad" bacteria will taste (or smell) worse. The wrong yeast will lead to flat bread. The good news: An unfortunate starter–no matter how funky–isn't likely to make you sick. The bad news: No matter how experienced you get, making starter remains more art than science.

But it was an art that worked for thousands of years. Again, I'm baking-impaired, but I had no idea that sourdough was the world's first type of rising bread. In fact, it was really the only type of rising bread until the middle ages, when European bakers began using the yeasty byproducts of beer-making, instead.

The first sourdough bread makers were the ancient Egyptians. Back in the early 1990s, Wood worked with National Geographic archaeologists to recreate Egyptian bread, using the wild yeasts and bacteria of Cairo and a recipe based on evidence uncovered at an ancient bakery once used to feed the men who built the smallest of the Giza Pyramids in 2470 BCE.

Egypt isn't the only place Wood has traveled in search of sourdough. Wood lived in the Middle East for several years and spent much of that time collecting samples of generations-old starter from bakeries throughout the region. Wood sells some of these starters online at Sourdough International, and he's also written a couple of books about the geographical and archaeological variations in sourdough recipes.

The Exploratorium also has some pleasantly non-intimidating instructions for making your own starter.