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Perhaps as early as 40,000 years ago, early humans were building a bond to last the history of mankind.
It was then, as one leading theory of domestication goes, that wolves began to scavenge near human settlements for leftover food. The more human-tolerant wolves gained an evolutionary advantage and, over the course of generations, became tame enough to resemble our modern mutts. Once domesticated into what we know now as dogs, man could even select for specific behaviors — creating specialized companions who could track, hunt and even shepherd livestock.
Today, we use dogs to find earthquake survivors trapped in rubble, detect seizures and heart attacks before they happen, sniff out a dizzying list of dangerous substances and much, much more. At the very least, they’re our dear companions — fiercely loyal, loving and terrific listeners. It’s really no surprise dogs are nicknamed “man’s best friend.”
But man has another best friend, and a semi-imaginary one at that. Admittedly, we might not be able to see this friend with the naked eye — and as we usually do with imaginary friends, we’ve forgotten about them as we’ve gotten older. But the two of us have been inseparable since the early childhood of homo sapiens, and they’re more important to humanity now than ever before.
Allow me to reintroduce you to Saccharomyces cerevisiae — better known as baker’s or brewer’s yeast — aka mankind’s favorite single-celled fungus.
This isn’t the first time you’ve met. You may already recognize them from your sourdough starter — or favorite alcoholic beverage — thanks to their ability to ferment. As they eat sugar, particularly in low-oxygen environments, the fungi produce carbon dioxide gas and ethanol — perfect if you’re looking to make bread rise or turn fruits and grains into an intoxicating brew.
As it turns out, it was through these common interests that man and yeast first crossed paths. A 2018 study found evidence that humans may have been brewing beer 13,000 years ago in a cave in modern-day Israel, and scientists now know pre-humans began evolving to become metabolize alcohol roughly ten million years ago. They might not be able to guard the house, but how’s a few epochs of loyalty for you?
All that is not to say anyone knew then that yeast was behind it. Until Louis Pasteur discovered fermentation was caused by living organisms in the 1850s, the domestication of wild yeasts over time happened mostly on accident.
Yeast lives pretty much everywhere — you can find it on most plants, floating through the air, buried in the soil and even on your skin right now. One hypothesis proposes when early humans began to store their food underground, yeast’s low-oxygen superpower kicked in and fermented their stores into longer-lasting — albeit tangier — ones.
Once we started baking and brewing with ol’ Saccharomyces, we started inadvertently selecting for tastier strains by “backslopping” — adding some previously fermented food into the next batch to jumpstart the fermentation process.
The results were tastier than the name suggests. Yeast can go dormant for long periods of time, so even making the next batch of a successful dough in the same place or with the same tools would allow the new dough to inherit the same successful strains. In fact, a team of researchers recently revived what they believe is 4,000-year-old yeast from ancient Egyptian pottery and baked a loaf of bread with it.
But yeast’s many uses only begin with our beer, wine and bread. Thanks to modern science, we've genetically modified yeasts to produce chemicals like bioethanol, a gasoline additive and sustainable fuel. They produce many of our medicines, too — including prescription drugs like insulin and components used in vaccines.
Yeasts, and particularly Saccharomyces, are also vital model organisms. They’ve allowed us to successfully study Alzheimer’s, Parkinson’s and Huntington’s disease. Leland Hartwell, the cancer researcher who won a Nobel Prize for his work in 2001, conducted his experiments in baker’s yeast.
Hartwell used the yeast to study the cell cycle; the series of steps a cell follows to grow and divide. Specifically, he used them to uncover more than 100 genes that govern how cells control their division and check for DNA damage. These genes are shared by humans, and mutating them can lead to runaway cell growth and eventually cancer.
From the soil where early humans buried our food to the bioreactors producing our chemicals and medicines, yeast has been there for us.
No other companion has been more loyal, more giving or more loving than our friends from the fungal kingdom. They might be microscopic, but I think they make even better listeners than dogs — and so long as you keep feeding them, you won’t outlive them.
Spencer Schaberg (he/him) is a junior studying microbiology.
