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  • Around 10 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 chimpanzeesand

  • 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, the 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 a lot of the same things we do.

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

  • process.

  • Now, were 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 meattheyre 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 produced 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; 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 the 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 prettykinda 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 couldve

  • posed a big problem.

  • Instead of just getting the sugars and starches they were used to, now they were absorbing

  • alcohol, too.

  • And if their bodies couldn’t digest it, the ethanol couldve quickly made them sick.

  • Sort of like getting a bad hangover, but after only a few sips of booze.

  • Luckily for these primates, 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 the risk of getting sick.

  • Ok but eating fruit that’s fallen on the ground, that's one thing

  • But what about drinking milk that’s gone sour or eat meat that’s kinda rotten.

  • How could either of those things be appetizing?

  • Welp, some researchers think 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, like we talked about in our episode

  • about what real paleo diets were like.

  • Today, human taste buds interpret different foods as being sweet, salty, sour, bitter

  • or umamiwhich 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 cerealsthey 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 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 flavorlike 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 valuelike, say, vinegar.

  • But!

  • Foods that have been fermented or are rich in vitamin C are often 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 mightve 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.

  • Ok but

  • Still, the idea of letting microbes digest meat before we get to it sounds like a recipe

  • for food poisoning, right?

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

  • Some researchers think that our distant relatives, Homo erectus, may have been eating fermented

  • meatthough 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 wouldve 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 kinda 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 wassour, andcheesy 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 couldve been used by human ancestors

  • and relatives, including Neanderthals.

  • Thanks to a number of archaeological sites associated with Neanderthals, scientists think

  • they ate a lot of meat.

  • And it wasn’t just scavenged meatthe 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 a corner store to get some lime 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 exposed to

  • oxygen, heat, light, and elevated pH levels.

  • Now, the only places where vitamin C is found in most animalsbodies are 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 wouldve 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 mightve

  • protected the fermenting meat from oxygen exposure, so the vitamin C wouldve 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 breador 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 mortarsstones that had been hollowed out for grinding and

  • storing foods.

  • And researchers found starches in the mortars that showed signs of having been mashed and

  • fermented.

  • So the people who made those mortars were making alcohol!

  • Whatever drink it was, was probably very low in alcoholic content, but it’s still considered

  • the earliest known evidence of making fermented beverages.

  • Since then, fermentation has become a fundamental part of the human diet.

  • Weve 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, to bacteria that help with digestion, and

  • make some foods easier to digest, 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 ancestorscomplex and sometimes

  • risky relationship with fermented foods, going back to that primate ancestor some 10 million

  • years ago.

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

  • So, cheers!

  • So now that weve made you hungry, I guess, be sure to watch our other human diet episode, “The

  • Risky Paleo Diets of Our Ancestors”, and for more on our evolution check out theHuman

  • Evolution Learning Playlist”.

  • Thanks to this month’s sweet Eontologists: Lucan Curtis-Mahoney, Sean Dennis, Jake Hart,

  • Jon Davison Ng, Patrick Seifert, and Steve!

  • Pledged your support at patreon.com/eons and become an Eonite.

  • And as always thank you for joining me today in the Konstantin Haase studio.

  • Subscribe at youtube.com/eons to learn more about our ancient past.

Around 10 million years ago, one of our primate ancestors was searching for food on a forest

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B2 中高級 美國腔

我们如何弄清发酵(How We Figured Out Fermentation)

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    joey joey 發佈於 2021 年 05 月 02 日
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