This article is the sixth and probably last article in a minseries of six articles (see the first, second, third, fourth and fifth articles here) about civilization, fungus, and alcohol.

Very little is known about the beginning of the story of humans and yeast. Did it start in one place? Did it start in many? Did yeast independently colonize human settlements (and beer, wine, sake, bread and the rest)? Or was it one beginning that, with the spread of culture and humans, led to the rest? What is known is that with yeast, things changed. A single species of yeast, one out of thousands, ferments our beer, wine, bread, rum, and even a fairly long list of fermented foods and beverages of which you have never even heard. Because of this species, our cultures changed. Our diets changed. Agriculture arose or changed. Our bodies may even have changed. The yeast, throughout this change, has benefited far more than we have. There are more individual yeast organisms in wineries and breweries in France than there have been humans on Earth. It has been suggested that the differences among human populations in their response to alcohol is, in part, a function of the evolution of some but not all human populations in response to yeast and alcohol. Surprisingly little work has been done on the big questions in the story of yeast and humans. Although, yeast has been one of the best-studied laboratory organisms, the study of its history and tangled relationship with humans is nascent. For all of these reasons, when it came time to conclude this series, although I had said I would write about the story of yeast, I had second thoughts. I was not sure how to conclude. So little is known that the story of yeast and humans from the yeast's perspective I felt more an urge to go do a study on yeast than to summarize its story. It needed meat, or at least malt. One can only say so many times that “much remains to be learned.” Instead of writing, I decided yesterday to go with my family to the Dordogne valley in France, not far from where we are now staying in Toulouse ,to explore. The trip, and some good French wine would clear the mind.

The Dordogne Valley is a long and flat plain, bordered on either side by limestone cliffs. The cliffs are large and yet it is not the size of the cliffs that presents a mystery to someone walking through the valley, it is the caves. Augured nearly everywhere into the limestone, they beg explanation. In some, great discoveries have been made. In others, it appears no one has yet really set foot. It is the others that add an air of real possibility to the whole scene. What has been found in these caves and what remains to be found offers as important a perspective on the history of early humans as there is to be had.

The caves seemed to have nothing whatsoever to do with yeast. The oldest among them are 17,000 years old and the youngest 11,000 years, just before the dawn of beer. We would enter one of these older caves, Grotte des Combarelles. This cave would be a break for me. Sometimes distance adds perspective. Sometimes so does putting your head, and the rest of your body, into a hole.

It was cold on the day my family and I entered the caves. We were bundled tightly, but as we entered Grotte des Combarelles, we warmed. The cave radiated the heat that stays in the Earth even when everything above it cools down. It was the same warmth our ancestors would have found, a refuge. The first hundred meters of the cave or so were as close as I have ever been to walking into the nest of an ant. The walls were bumpy with erosion. I had the feeling we might, around a corner, discover an enormous queen, but maybe this is only how ant biologists feel when going through tunnels. As I thought all of this, we came around a corner and the guide shone her light on a wall where we saw what we had come for. There, in the lantern light, emerged bison. They were artful, realistic, and, in the connection they offered across thousands of years, magical.

As we continued, other animals came out. Reindeer. Oh, a seated man! More bison. An aurochson (ancestor of the cow). Brown bear. Two naked women. A wooly mammoth. A WOOLY MAMMOTH! House-shaped symbols from which the meaning has been detached. Each was carved into the cave wall, carved by a man or a woman who would have laid on his or her belly, with an animal fat flame, drawing. The caves were deep, and in that time, difficult. The artist must have wanted badly to do art in order to crawl so far in and work under such difficult conditions. What is rendered is art. I know it when I see it. And our cave, the cave we were standing in, was just one of many. Murals of life were carved and painted across the walls of dozens of caves across the region, by many different hands across thousands of years. In and of itself, this reality was stupefying. Words fail, especially when I’m trying to speak French.

[Image 1. A sketch of the mammoth drawing we saw in one of the caves we entered. Drawing by Joseph Déchelette]

One is struck, in looking at these paintings, by the humanity they imply. The artists looked out at their world and when they chose to record things, they recorded what scared them (bears, lions and mammoths), what they ate (bison and again the mammoths), and then, of course, women. It does not take an overactive imagination to recognize in these drawings the hand of someone like me, like you, someone human.

These people are the before scene in the story of agriculture--before agriculture-beer, wheat, barley, yeast or any of the rest. They caught and killed wild bison. They ran around with mammoths, killed those too. They drank from rivers. Here, underground, I was not doing a story. I was just present, among ancient drawings, at once at awe and ready to sneak past the guide to the darker parts of the cave where more paintings lay. Just seven years ago, a new passage in this very cave was discovered and within it many new paintings. I was not thinking about yeast at all. My mind felt clear and wild. And then I saw it…

As the guide shown her light around, getting ready to speak again, I spotted something in a neglected corner of the cave. It was a circle with two smaller circles inside it, circles of different sizes. I knew I had seen it before, and then I remembered where. It looked just like yeast. Here it was, the first indication of when yeast had arrived in a human society, a drawing of it no less. There were bears, bison, and mammoths, but this was yeast. Yeast, mind you. Here it was, a cave painting of a microscopic species.

Yeast in particular, and microscopic life in general, is a powerful force in our lives. Especially with the advent of agriculture, microscopic species would become the major additional players one would want to add to a cave wall. There were, of course, the new pathogens that chased us once we began to farm. But there was also yeast. For the ten thousand or so years we relied on yeast, before it was known to exist, it would have been pure magic. It still is. It can turn old wheat and sprouting barley into beer. It can turn mashed up grapes into wine. It can make bread magically expand with air and flavor. Here, if any creature deserved to be added to the cave wall once the first hints of agriculture came, was the creature. Somehow the people of the Dordogne valley had seen clearly what would take so many years to see clearly again. Having found the image, I could retire.

[Image 2. Civilization's yeast, by Masur, not cave artists.]

I can't overemphasize how amazing this discovery was . In taking a tour through a cave I had discovered the first clue to the beginning of the long story of humans and yeast, a story that is known to have started just a thousand years or so after this cave was painted. Not only that, I had discovered it just at the time I needed to resolve my series on alcohol, fungus (the yeast) and civilization. One hopes after years of hard work to make such a discovery. I had made it in a morning on the perfect day. I smiled a smirky, knowing, smile, as the guide began to talk about the carving. Or, at least I did until the moment when she pointed out what, in retrospect is now very obvious. It was not yeast at all, but instead, a human face, with two round eyes.

Later that day, my family and I left the Dordogne Valley for Toulouse. We left behind the caves, much to my dismay and as we did, we drove through a far clearer symbol of the story of yeast than any imagined cave drawing, miles and miles of vineyards dedicated to grape vines, which are, in turn, dedicated like much of what we do, to the yeast, whose taste is complex and will remain, I suspect, hard to fully explain.

The End (for now)

Table of evolutionary contents: Here you can skip ahead or backward to the other chapters in the story of the other species in our daily lives, whether they bethe cow, the chicken, the hamster, bacteria (on Lady Gaga, on feet, in bathrooms,as influenced by antimicrobial wipes, as probiotics, in the appendix), pigeons and urban gardens, house sparrows (to be published next week, stay tuned), predators,diseases, dust mites, basement dwellers, lice, field mice, viruses, yeast, the fungus that produces penicillin, bedbugs, houseflies, or something more.

Or for the big picture of how Rob thinks these stories come together to make us who and who we are, check out The Wild Life of Our Bodies. Rob Dunn is a writer and evolutionary biologist in the Department of Biology at North Carolina State University. Find him on twitter at robrdunn. Find him in person somewhere in Europe with his family while they are all on sabbatical.