Ahh, summer. A time for road trips and a chance to put a dent in that pile of books you’ve been meaning to read. It makes sense to combine the two, yet for many people reading in the car is simply not an option unless they want to make a detour to Vomitville. So what’s the deal with literature-induced carsickness?

Let’s look at this in evolutionary terms: Our brains are a lot like anxious first-time parents, and we are their babies, just learning to crawl. A good deal of our brains evolved thousands of years ago, ages before cars or books existed. They came of age at a time when predators and eating the wrong plant were real dangers. In order to survive, our brains became hypervigilant, developing stress responses to help us fight or flee and learning to induce vomiting at the first sign of poisoning. 

This world is not strange to us, because we were born into it. We know that riding in a car and reading a book are perfectly mundane activities. Our brains, however, aren’t so sure. 

Scientists believe it works like this: When we walk, our bodies are moving and traveling at the same time. This, says your brain, is the only way movement can work. But when we sit in a car, our bodies aren’t really moving. They’re just traveling. Signals from your muscles, nerves, and eyes tell your brain that you’re stationary. At the same time, the fluid in your ears is sloshing around, which tells your brain you’re definitely going somewhere. So your brain is getting two conflicting messages at the same time. One long-standing theory is that your primitive brain interprets this neurological confusion as a sign you've been poisoned. 

Time to puke. 

So why do books make it worse? Think about one of the most common cures for carsickness: looking out the window. Taking in visual proof that you’re moving is a great way to soothe your panicked brain. The reverse is also true: Focusing your eyes on a single, static object doubles down on the sensory mismatch and confirms your brain’s conclusion that something is very, very wrong. 

We do have some good news for you: A lot of people grow out of carsickness. The longer your brain stays in this weird, contradictory world, the better it learns what’s truly helpful and what just leaves you miserable and barfing by the side of the road.

[h/t: Science of Us]