The Evolution of Tooth Decay

**Teeth: The Coolest Rocks in Your Face**

Teeth are essentially the coolest rocks you'll ever grow in your face—and I’m only half-joking. They’re made of millions of tiny mineralized crystals, much like rocks. However, unlike rocks, when these minerals start to degrade, your teeth can't heal themselves like bones or skin can. So, when you get a cavity, that’s a hole in your tooth that needs professional help to fix.

Now, you might think that before modern dentistry, people must have had terrible teeth, with cavities running rampant. And while some ancient humans did have cavities, they weren’t exactly eating candy by the handful or chugging energy drinks. Yet, it’s not as simple as saying, “We get more cavities now because we eat more processed foods.”

So, let’s take a trip back in time to figure out why humans have the worst teeth in the animal kingdom. The most common dental issue we face is cavities, also known as caries. Over 90% of us will experience at least one in our adult lives. The culprit behind this pesky tooth decay is a specific type of bacteria that lives in our mouths, particularly in the dental plaque that forms on our teeth.

The main offender is the bacterium *Streptococcus mutans*. It breaks down the sugars in the food we eat and produces acidic byproducts. These acids erode our enamel, weakening it and making it more vulnerable to cavities. Other factors also play a role, such as saliva production, dental hygiene, and even genetics. But the biggest factor always circles back to sugar.

When we talk about “sugar,” it encompasses more than just candy. Starches found in foods like bread, rice, and pasta also contribute to cavities. Our craving for sugary and starchy foods dates back to long before farming or even before our species existed. As primates, our ancestors and living relatives mostly ate fruit, which is essentially sugar plus fiber. It’s no wonder that fossilized primates from as far back as 54 million years ago had cavities, just like some fruit-loving monkeys and apes do today.

However, even the sweetest-toothed chimps only have a cavity rate of around 45% across individuals, which is far less than the over 90% we see in modern humans. So, when did cavities really become a major issue for us? The short answer is during the agricultural revolution, around 10,000 BCE. This period marked a significant shift in human diets globally, leading to massive dietary changes.

Before farming, people hunted and gathered wild foods in their environments. Flashback to 1.5 million years ago, and early human relatives like *Paranthropus robustus* were eating a variety of plants, but not a lot of sugary foods. So, while they did have a few cavities, they had far fewer than later species like *Homo erectus*. Even Neanderthals had some cavities, though not many, despite carrying the *Streptococcus mutans* bacterium. Scientists have found DNA evidence of their oral microbiomes in the hardened dental plaque of Neanderthal teeth.

When we look at our own species, *Homo sapiens*, we see variations in how tooth decay affected different groups. Those who consumed more sugary foods typically had more cavities. For example, a site in Morocco, known as Les Grotte des Pigeons, from around 14,000 to 15,000 years ago, revealed that about half of the teeth and 94% of the people had cavities—a rate similar to modern industrialized populations. Compare this to most other hunter-gatherer societies, where only around 15% of teeth show signs of cavities.

But how did ancient people develop so many cavities without modern sugary snacks? Evidence suggests they ate large quantities of a particularly sweet type of acorn, which becomes soft and sticky when cooked, along with wild oats and legumes. However, the real explosion in cavity rates came with the advent of farming grains like wheat and barley, and it only got worse with increased food processing and the addition of sugar to almost everything.

We have ample evidence that once farming began, people around the world had the potential to develop cavity rates similar to what we see today. Additionally, *Streptococcus mutans* evolved along with our dietary changes. While ancient human relatives have dealt with this bacterium since at least the Neanderthal days, there was a spike in its genetic diversity around 10,000 BCE—coinciding with the advent of farming—and even more changes in the last 750 years as we began cultivating sugar actively.

Like any successful pathogen, *Streptococcus mutans* adapts to become better at exploiting its environment, which, in this case, means ruining our teeth. It’s even starting to develop resistance to antibiotics, so we may have to start worrying about it more in the future. The story of us, our teeth, and *Streptococcus mutans* is long, twisty, and far from over. But even though most of us will experience cavities at some point in our lives, at least we’ll live long enough to get them—something that can’t be said for many of the ancient people we’ve talked about in this video. Tooth problems are just part of the deal, but it’s a small price to pay for the luxury of eating candy in our pajamas.