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9 Biggest Unsolved Mysteries About the Human Body

Despite the fact that we spend our entire lives in them, there's still a whole lot we don't know about our bodies!

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Why do we have fingerprints?

We all know that our fingerprints are so unique that no two people have the same ones, not even identical twins. But why do humans have these swirly patterns on their fingers in the first place? For many years, scientists thought they were there to help human fingers grip things… but it turns out, fingerprints actually allow less of our skin to come into contact with objects than perfectly smooth fingertips would. So they have nothing to do with gripping. While there are a few theories about the evolutionary purposes of these unique patterns, including that they protect our fingers or provide touch sensitivity, scientists haven’t been able to figure out a definitive explanation. We bet you didn’t know that these other body parts are as unique as our fingerprints.

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Why do we have an appendix?

As an organ that causes many people lots of pain and whose removal has absolutely no effect on our bodies, the appendix seems to be more trouble than it’s worth. For many years, scientists, all the way back to Charles Darwin, were in agreement that, while a plant-eating human ancestor needed an appendix for digestion, it was only left over from evolution and had no real function for modern humans. However, another theory has become more and more popular in the scientific community lately, postulating that the tube-like organ actually houses and protects a host of good bacteria. We’ll have to wait and see if this theory is proven and the appendix gets its groove back. Here are the reasons we have 7 other bizarre body parts.

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Why do we have a dominant hand?

We’re so used to having a dominant hand, and identifying people as “righties” or “lefties,” that we probably take it for granted. But when you really think about it, the fact that we have one hand with significantly better functionality than the other seems a bit odd. Given everything we know about evolution and “survival of the fittest,” why haven’t we evolved to have two totally adept hands? It’s one of the biggest human body mysteries out there. Of course, there are some people who can use both hands with equal skill. Check out these facts you never knew about ambidextrous people.

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Why do we yawn?Why do we yawn?shutterstock (2)

We’ve been yawning since we were in the womb, and yet scientists still have yet to find an explanation for why we do it. While there’s no shortage of theories, the true reason for yawning remains a mystery. One theory suggests that we yawn to regulate the temperature of our brains, since sleep deprivation or boredom can cause our brain temperature to drop. Another suggests that we yawn to give our bodies a jolt, since our heart rates tend to increase and our eye muscles tense up after we yawn. Maybe both are true.

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Why do we have blood types?

Like the appendix, humans’ different blood types provide clues to our evolutionary history. Different blood types have varying abilities to fight off different infections, and scientists believe that they began evolving around 20 million years ago in human ancestors and other apes. “Combined with natural selection for certain blood types against certain infections, [evolution] produced the marvelous diversity of the human blood types that we see and recognize in this era,” explains Dr. Mohammad Mobayed of ProMedica Hematology/Oncology Associates. But what scientists don’t know is why. “No definitive theory or theories [explains] why blood types differ among humans,” says Dr. Mobayed. These are the reasons everyone should know their blood type.

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Why do we dream?Why do we dream?shutterstock (2)

“Humans spend nearly a third of their lives asleep, yet science has still very little understanding of how and why we dream,” says Caleb Backe, a Health and Wellness Expert for Maple Holistics. We know that dreaming occurs during REM sleep and that our heart rates increase when we dream, but we’re unsure about what purpose dreaming serves. A popular theory suggests that dreaming is how your brain sorts through the memories of the day, deciding which ones are valuable and which are irrelevant. Other scientists, though, believe that dreaming actually serves no real function and that it’s just what our unconscious mind does when untethered by our awake selves.

Why do we have viruses inside our bodies?shutterstock (2)

Why do we have viruses inside our bodies?

Convinced that the only living thing in your body is, well, you? Think again. Humans possess so many microbes inside (and on) their bodies that they actually account for a few pounds of our body weight. Plenty of them have good reasons to be there—they aid our digestion, they heal our cuts, or they battle illness. The majority, though, are viruses whose purposes we’re completely clueless about. Meet some of the microbes that live in and on our bodies.

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Why are other primates so much stronger than us?

In many ways, human bodies are extremely similar to those of other primates like chimps; they have very similar muscle structures. Despite that, though, our closest primate relatives are around 1.35 times stronger than we are. We developed more slow-twitch muscle fibers, which are less powerful muscle fibers, than other primates. However, these muscle fibers do allow humans to have greater endurance than other primates; they enabled early human behaviors like hunting and foraging. Today, they’re the reason a human can run a marathon while a monkey can’t. But despite all those human perks, the strength disparity is still significant enough to baffle scientists. If you’re feeling bad about your human weakness, have no fear: the human body still does plenty of incredible things every single minute.

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Why is laughter contagious?

Yes, laughter is contagious, and not just metaphorically so. Scientists have found that powerful emotions can actually cause the brain activity of different people to sync up. “Studies show that [laughter] is linked to being social creatures. In fact, psychologists have found that humans are nearly 30 times more likely to laugh when in social situations,” explains Backe. “The current theory suggests that laughter is contagious because humans are empathetic beings.” Our brains release endorphins when we laugh, and these chemicals cause us to feel safe and at ease. So while we may not know exactly why our laughter is infectious, one thing we do know is that it feels good. So laugh away! Next, check out some other science mysteries no one has figured out (yet).

Meghan Jones
Meghan Jones is a Staff Writer for who has been storytelling since before she could write. She graduated from Marist College with a Bachelor of Arts in English and has been writing for Reader's Digest since 2017. Her creative nonfiction piece "Anticipation" was published in Angles literary magazine in spring 2017. Meghan is a proud Hufflepuff and member of Team Cap.