You laugh at jokes. You laugh at guys getting kicked in the crotch. You laugh when you and your girlfriends get together to talk about how adorably clueless all men are. And yet science still can't vouch for why exactly we do this. We start laughing around 3.5 or 4 months old and scientists believe it's a way to build relationships rather than a response specifically to something funny. Researchers are still trying to figure out what triggers laughter in the brain and why being tickled, which feels a bit like torture sometimes, makes us laugh so much.
Can you imagine the first kiss in history? It makes you wonder if those people just thought, "What would happen if we mashed our mouths together?" or if it's always been a part of human nature. We may never know, though scientists are certainly looking into it. These special kiss researchers are called philematologists and they've come up with theories on the origins of kissing and looked at the biological effects. Some say kissing is a learned behavior, evidenced by the fact that 10% of humans don't kiss at all. Other scientists say that kissing is an instinct and point to the fact that some animals do it. Whichever way it is, we're just thankful that locking lips is an accepted way of showing affection.
This may not be a strictly human behavior, but it's puzzling nonetheless. Why is it that we open our airways to take big gaping breaths? And why do we start yawning when we see someone else doing it, or even when we just think about it? (Are you yawning yet?) The answers are unclear; different theories attribute it to a number of causes. Some believe it's simply an involuntary act that happens when your lungs need more air. Some say the contagious yawn is actually a way of empathizing with the original yawner. Still others say it's all just a way to cool off our brains.
You know the feeling. You just tripped on the street, were talking about someone when they were right behind you, or got called on in a class you were not at all prepared for, and suddenly you can feel your whole face begin to burn. Blushing is a common response to embarrassment, but scientists aren't sure why it happens. The how is explained by increased adrenaline allowing the blood vessels in your face to expand, allowing more blood, and thus redness, into your cheeks. Making blushing even more mysterious is that blushing from alcohol or sexual arousal has nothing to do with adrenaline, according to scientists.
Dreaming is one of our most fascinating behaviors, partially because it's impossible to share with others. Sure, you can try to explain that strange nightmare you had, but you find yourself without a lot of explanations: "We were in our house, but it wasn't really our house. Somehow you were there, but then you were someone else. Wait, why was it scary again?" Dreams themselves are hard for us to hold onto, and the explanation for why they occur is equally challenging to grasp. Scientists have been theorizing on the purpose of dreams for centuries, but we're still as far away from an answer as ever. Some guesses are that we're practicing our response to a frightening situation, that our brains are sorting through the knowledge we've gained during the day and purging themselves of the unnecessary bits, or that we are working through our emotions. Conclusive evidence for any of these theories seems totally out of reach.
Hiccups, the annoying, squeaky jolts you sometimes get, are a reflex of some kind, but exactly what they're reacting to is a mystery. A hiccup occurs when your diaphragm contracts and you inhale suddenly; the sound is produced by your vocal cords closing quickly. People can get hiccups from emotional distress, swallowing too much air, drinking a lot of alcohol (classic), or even just consuming a hot beverage. All these causes make it hard for doctors to pinpoint exactly what's going on in the body. Common ideas are that something irritates your diaphragm, causing it to spasm, or there's a disruption in your nerve pathways.
Since we've been crying since birth, we rarely think about why we do it. But we're the only species that we know of with water gushing out of our eyes when we experience emotions. Scientists think it may have done something positive for the advancement of our species, perhaps acting as a signal that enemies wouldn't pick up, and that's why we've continued to do it over the years. We now cry when we're feeling all kinds of emotions, ranging from sadness to joy, frustration to pain, even though we're not trying to hide our weaknesses from predators. Crying is also a way to provoke empathy from others, which may have built strong communities among our ancestors.
While blinking has the obvious benefit of moistening our eyes, we do it more than is necessary to perform this function. Researchers think the reason is probably psychological because we blink more as adults than we did when we were babies — 10 to 15 times a minute compared to just once a minute for infants. We still don't know exactly why this is, but they've found that we blink less frequently when we're really engaged in or concentrated on what we're doing.
Feeling a phantom limb
We hope you will never experience this sensation, but it's one of the most mysterious phenomena that happens to humans. Amputees often say they feel like their amputated limb is still there. Some can just feel it, while others can feel actual pain in their phantom limb. Doctors aren't sure why this happens but they have plenty of complicated explanations they think could account for it, such as severed nerve endings and the reorganization of the somatosensory cortex. We may never understand where these phantom limbs come from, but many are treated with antidepressants, electrical spinal cord stimulation, or even using a mirror box to visualize the phantom limb and practice relaxing it.