We do a lot of stuff every day that most of us never even think about. Its too bad, because the explanations behind some of our most ordinary functions are quite fascinating.

Though its mostly thought of as an old wives tale, the idea that gentlemen prefer blondes has biological grounding. The average woman with blonde hair is likely to have light skin, and skin with a paler pigment will more noticeably show physical defects. So a male prefers female mate with blonde hair because he can more easily see how healthy their offspring will be.

Of course, females seek out and avoid the same qualities in males, so perhaps the adage should be that everyone prefers blondes.

There are many reasons for someone to be unfaithful, but aside from the psychological, its possible some people literally have cheating in their DNA. Scientists have discovered a gene they call RS3 334, which is colloquially becoming known as the divorce gene. In tests where men and women were asked to fill out detailed (and anonymous) questionnaires about their marriage, couples where the male of the relationship had one or more of the RS3 334 genes scored low, both describing unhappiness and frequent domestic troubles. It is thought the gene affects the bodys vasopressin release, a chemical responsible for human bonding and monogamy.

A lot of actions have become so ingrained in our culture that we dont stop to think about why we are doing them. Hugging is essentially grabbing someone for no reason and with no outcomes or time limit planned. It seems strange when analyzed like that, but the reasons can be explained: close contact with another human, such as that experienced through hugging, is linked to the release of oxytocin, a hormone responsible for attachment and trust. Its particularly useful in a relationship because the body contact occurring during sex releases oxcytocin with the aim of pairing the two together for raising offspring.

Dont have anyone to cuddle? Dont worry: your brain also releases oxytocin for things like meaningful eye contact, generous acts, and even patting a dog.

The fear of strangers most children feel can be explained chemically. Oxytocin, the very same hormone that helps us bond with people we are close with, will also compel us to distrust people we dont know.

There have been studies where participants inhale either oxytocin or a placebo and engage in group games with incentives to cooperate. When the groups featured people the participants already knew in some manner, the oxytocin caused their cooperation to risebut when the groups consisted of strangers, it caused cooperation to fall. This is possibly left over from our ancestors, who needed to trust their own tribe while maintaining a healthy, defensive fear of other tribes they came across.

We scratch all the time, but do we benefit from it at all? Scratching, or more accurately having an itch, is your bodys way of eliminating potentially harmful irritants or external objects. For example: an ant crawls onto your foot, so that area of your foot itches; you scratch that area and brush the ant away.

So it does help us, but why do we scratch so often? Its not like we are covered in bugs all the time. Well, from an evolutionary standpoint it makes sense to scratch at anything that might be dangerous. While scratching something that wasnt a threat is fine, not scratching something that is dangerous can lead to problems.

Someone offers you some chocolate. On one hand, you want to eat it, but on the other hand you are worried about weight gain. You make a deal: I can have the chocolate now, as long as I promise to go the gym tomorrow. Who exactly are you making that deal with? Technically, another personat least according to your brain.

Its severity differs for everyone, but in many cases the same part of the brain that lights up when you think about others is also used to think about your future self. Subconsciously, you literally consider your future self a different person.

Laughing is another activity that, when analyzed, seems absurd: a series of strange whooping noises following any number of things a human might find amusing. The areas of the brain that regulate laughing also regulate breathing and speech, so laughter is a very primal part of our functioning, so it surely has a purposebut what?

Scientists think that when we laugh, we communicate a playful intent, indicating to others we trust them as a group member. This explains why laughing is contagious, and tests have shown that humans are far less likely to laugh when alone.

Everyone knows we sleep at night and wake in the daybut what exactly controls that? Most of us cant make ourselves fall asleep or wake up at will, so what does?

The answer is melatonin. In the morning, exposure to light triggers a variety of chemical and hormone releases that get us going and assist us in our daily activities, and the same thing occurs for the opposite reason at night. Melatonin is a natural hormone that helps us sleep. Its made by your pineal gland which only turns on when darkness occurs. Melatonin levels will stay fairly high for roughly 12 hours before exposure to light the next morning causes them to decrease.

The problem is that our pineal gland doesnt understand artificial light, so being in dark rooms during the day or bright rooms at night drastically affects our body clock.

Have you ever wondered why people lose their temper? Anger and aggression are perhaps the feelings we feel like we can least control, and sometimes we really do have no control at all. The amygdala is one area of the brain that has been shown to cause aggression, and damage to this area results in amplified aggressive behavior. The prefrontal cortex receives impulses from the amygdala and processes other information to decide if it should take action. Damage to the amygdala through physical trauma, tumor, or birth defect can result in those impulses becoming overwhelming, causing a urges and impulses towards aggressive acts the person might not morally agree with.

Pedophilia is of course not a common or acceptable trait for humans, but in some cases it can be explained physically. In 2000, a married man suddenly developed a severe pornography addiction and pedophilic thoughts accompanied by excruciating headaches. He sought help and it was soon discovered that the man had a tumor the size of an egg growing in his brain, pressing on his prefrontal cortex, which (as previously discussed) regulates urges. When the tumor was removed, the mans behavior returned to normal and his unsavory sexual desires evaporated.

This kind of case is rare, but nevertheless possible. While we dont normally experience such severe swings, it raises the question: do you control your actions or is it just all those chemicals?

Scott Friggin tweets.

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10 Common Human Behaviors Explained With Science - Listverse