(host) Around ten million years ago, one of our primate ancestors was searching for food on a forest floor.

This primate was one of the last common ancestors of humans, gorillas, and chimpanzees, and it was slowly adapting to a new way of life, splitting its time between the trees and the ground.

And this lifestyle opened up all kinds of opportunities for finding food, like scavenging fruits that had fallen from the trees.

But some of these new foods could hold some surprises.

Once they landed on the ground, their fruits often acquired a little kick.

This happened through the process of fermentation.

Bacteria or yeast got into the fruit and started feasting, converting the fruit's carbohydrates into new chemicals, including ethanol, a kind of alcohol.

But thanks to a recent adaptation, instead of getting sick from the boozy fermented fruits, that primate could digest them safely and get more calories at the same time.

This new superpower would open up a whole new nutritional landscape for us-- fermented foods.

It took millions of years for hominins to go from enjoying nature's own fruit punch to making things like kimchi and beer.

But figuring out how that process unfolded has required a lot of scientific sleuthing.

Since these foods don't leave much of a trace in the fossil record, scientists have had to rely on a whole bunch of different disciplines, from genetics to experimental archaeology, to solve the mystery of our relationship with fermentation.

And it turns out, the very evolutionary path of our species may have been shaped, at least in part, by the delicious chemistry of fermentation.

On the most basic level, fermentation is simply when microbes metabolize certain foods, Yeast and bacteria, for example, eat lots of the same things that we do.

They use enzymes to digest their food, and what they leave behind are byproducts of that process.

Now, we're used to thinking of fermentation in terms of things like bread or cheese or wine, but it can happen to pretty much any kind of food molecule, carbohydrates, lipids, even proteins.

Fruits, vegetables, grains, fish, red meat-- they're all fair game as far as microbes are concerned, and hominins have benefited from this process when certain microbes have gotten into our food first and produce the right byproducts.

For example, lactic acid bacteria are some of the most common microbes found in fermented foods today, like sourdough bread and cheese.

When those bacteria get to work, they produce lactic acid, and the acidic environment that they create keeps other more dangerous microbes from getting into the food.

The same thing happens when microbes produce ethanol, also known as alcohol.

Perhaps you've heard of it.

The alcohol helps make the environment around the food inhospitable to harmful bacteria.

So humans didn't invent fermentation.

We just took advantage of the work that microbes were already doing and eventually figured out how to harness that work to make foods that we wanted and that were safer to eat.

But for our ancestors, fermented food probably seemed pretty dicey.

For example, let's go back to that fruit on the forest floor.

When our primate ancestors started eating fermented fruits, the ethanol in them could have posed a big problem.

Instead of just getting the sugars and starches that they were used to, now they were absorbing alcohol, too, and if their bodies couldn't digest it, the ethanol could have made them sick quickly, sort of like getting a bad hangover but after only a couple sips of booze.

Luckily for these primates, though, they acquired the ability to metabolize ethanol much more efficiently than others had in the past.

A random genetic mutation led to a change to a digestive enzyme known as ADH4 that shows up in huge amounts on the tongue and in the esophagus and stomachs of primates.

And this new version of ADH4 was 40 times better at digesting ethanol, which meant a new source of calories was suddenly available that didn't pose a risk of getting sick.

Okay, but eating fruit that's fallen on the ground, that's one thing, but what about drinking milk that's gone sour or eating meat that's kind of rotten?

How can either of those things be appetizing?

Well, some researchers think that it has to do with how our sense of taste evolved.

When our hominin ancestors were hunting and gathering to get their food, their sense of taste was crucial for identifying which foods might be safe and which might be dangerous.

And the price of being wrong could be pretty high, as we talked about in our episode about what real paleo diets were like.

Today human tastebuds interpret different foods as being sweet, salty, sour, bitter, or umami, which is a savory flavor.

Sweet and salty flavors come from nutritious or calorie-dense sources, so we tend to seek those foods out.

Take carbohydrates, which can often taste sweet.

Carbs aren't just the main source of calories in bread and breakfast cereals.

They also account for the calories in fruits like bananas or vegetables like yams.

As for salty foods, some researchers think that we seek them out because we sweat and lose sodium, so we need more of them.

And then there are the bitter flavors, which have helped us interpret that taste as a warning that something might be poisonous.

That's because most compounds that produce a bitter flavor, like those in milkweed plants, are toxic at different concentrations.

But maybe the weirdest taste adaptation we have is the ability to taste sourness.

Most chemicals that produce sour flavors don't have much nutritional value, like, say, vinegar, but foods that have been fermented or are rich in vitamin C often taste sour too.

So it's possible that our ability to taste sour foods helped us identify fermented foods specifically because those foods added important nutrients to our diet.

Finally, our preference for that hard-to-define flavor known as umami might also be related to fermentation.

Today the flavor is usually associated with things like cooked meat and fermented products like miso and soy sauce, but raw meat doesn't have that umami flavor.

Plus, it requires more energy to chew and digest than cooked meat.

So it's been suggested that our preference for umami might have evolved in response to the nutritional benefits of eating foods that microbes had already pre-digested for us.

The flavor was a signal that microbes had already done some of the work.

And just like our ability to taste sweetness, our taste receptors for umami seem to have deep evolutionary roots and are shared by most land vertebrates.

Okay, but still, the idea of letting microbes digest meat before we get to it sounds like a recipe for food poisoning, right?

But in their proper conditions, this type of fermentation can actually be beneficial.

Some researchers think that our distant relatives, Homo erectus , may have been eating fermented meat, though there's not any concrete archaeological evidence for this.

But it's possible because fermented foods didn't require specific tools for their preparation.

Homo erectus literally would have just had to stash the meat somewhere and wait.

For example, we know that fermentation can happen if meat is buried or submerged in water.

In fact, one paleontologist in the 1990s demonstrated this in a pretty convincing, if kind of odd, way by submerging a dead horse in a pond in late winter.

And, sure enough, between the cold and the low-oxygen environment at the bottom of the pond, by spring, the horse meat was sour and "cheesy smelling"... but also totally free of pathogens and safe to eat.

I am so hungry right now.

So, anyway, it's at least possible that techniques like this could have been used by human ancestors and relatives, including Neanderthals.

Thanks to a number of archaeological sites associated with Neanderthals, scientists think that they ate a lot of meat, and it wasn't just scavenged meat.

The animals were mostly adults and showed evidence of being butchered.

So the assumption was that Neanderthals were big-time carnivores, relying on meat for fat and protein, but an anthropologist named John Speth was puzzled over how they avoided getting scurvy.

This is a disease that happens when we don't get enough vitamin C. It's killed millions of people throughout history and can still be a problem today.

Neanderthals couldn't exactly have gone to the corner store to get some limes to squeeze on those rhino ribs or whatever.

Plus, vitamin C is one of the most unstable vitamins.

It's easily leached out of foods by water, and it quickly breaks down when it's exposed to oxygen, heat, light, and elevated pH levels.

Now, the only places where vitamin C is found in most animals bodies are in the organs, including the brain.

So, if Neanderthals were eating a lot of meat and the vitamin C in animal organs degenerates when it's cooked or exposed to oxygen, how did they get their vitamin C?

Speth had a hypothesis.

Maybe the Neanderthals were fermenting the meat.

This would've preserved the vitamin C, while also making the meat easier to digest without needing to cook it.

If the Neanderthals had stashed those meats somewhere for safekeeping, that might have protected the fermenting meat from oxygen exposure, so the vitamin C would have been more stable.

But would they have gotten sick from eating something that was kind of rotten?

Maybe not.

Speth pointed out that there are a number of cultures today that have been fermenting meat for centuries, like the Inuit, who bury meat in pits lined with acidic leaves.

The leaves, along with the acid produced by fermentation, make it difficult for dangerous bacteria, like the ones that cause botulism, to survive.

As Homo sapiens spread around the world and explored new environments, fermentation came to play an even greater role in our relationship with food.

It even figures into one of the biggest questions in anthropology.

Did we start practicing agriculture so that we could bake bread or so that we could brew beer?

Don't make me choose.

The earliest evidence of brewing comes from a burial site in Israel, which has been dated to 13,700 years ago, and the burials include several mortars-- stones that had been hollowed out for grinding and storing foods.

And researchers found starches in their mortars that showed signs of having been mashed and fermented.

So the people who made those mortars were making alcohol.

Whatever drink it was, it was probably very low in alcoholic content, but it's still considered the earliest known evidence of making fermented beverages.

Since then, fermentation has come to play a fundamental part of the human diet.

We've fermented dairy products into cheese and yogurt, grains and grapes into alcohol, vegetables into pickles and kimchi, and even eggs and meat.

Fermented foods give us access to vitamin C and to bacteria that help us with digestion and make some foods easier to process so our bodies don't have to work as hard to convert them into energy.

So a lot of who you are has been informed by our ancestors' complex and sometimes risky relationship with fermented foods, going all the way back to that primate ancestor ten million years ago.

It's in your tongue, in your brain, in your gut, and in your DNA.

So cheers.

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