Everyone loves to picture themselves as the captain of their own ship, steering every decision and, at the very least, every twitch of their own flesh. The idea of bodily autonomy is as common as a morning coffee—people agree you have the right to choose what you do with your own body. You can opt out of a medical procedure, you can ink your skin, you can style your hair, you can pick out the outfit you feel most confident in. In short, you’re in the driver’s seat… most of the time. Except when you aren’t.

There are whole systems inside you that run on autopilot, completely out of your conscious reach. Think about the relentless thump of your heart or the way your stomach churns after a big meal. While you can practice calming techniques to mellow a racing pulse, you can’t simply decide to start or stop the heart on a whim—thankfully, that’s a good thing. You can hold your breath for a while, but you can’t push it to the point of passing out without your body forcing a gasp for air. Digestion, blood circulation, hormone release—these processes happen without you having to think about them. So why does the brain hand over some jobs to the unconscious, while keeping others under direct command? And what about those borderline abilities—like breath control or bathroom timing—that feel like a gray area? Let’s dive into the astonishingly intricate machine that is you, focusing especially on the nervous system that pulls the strings.

5 Nervous Systems In General

Technically, you house two major nervous systems. The first is the central nervous system (CNS), comprising the brain and spinal cord, which acts as the command center, receiving and processing every bit of sensory data that streams in. The second is the peripheral nervous system (PNS), a sprawling network that extends beyond the CNS to reach every corner of your body. The PNS can be sliced further into the autonomic nervous system (ANS) and the somatic nervous system (SNS). Even deeper, the autonomic branch splits into the sympathetic, parasympathetic, and enteric subsystems. While we won’t unpack every single branch here, we’ll start with the sympathetic system, then glide over the autonomic and somatic portions to see how they dictate what you can consciously steer and what runs on its own.

Your CNS—brain and spinal cord—receives and reacts to all sensory input. The enteric nervous system, a specialized network governing digestion, is technically autonomous and largely out of your conscious reach, so we’ll set it aside for now. Let’s keep our focus on the peripheral system and see how its branches influence the tug‑of‑war between control and surrender.

4 Peripheral Nervous System

If the CNS is the hard‑drive of a computer, the peripheral nervous system is every peripheral device—cables, cameras, keyboards—that plugs into it. This is the conduit that shuttles information back and forth between the brain and the rest of the body. The signals traveling through the PNS dictate everything that happens without your conscious say‑so.

In plain terms, anything that isn’t the brain or spinal cord lives in the peripheral arena. Those are the actual nerves threading through muscles, skin, and organs, plus the sensory receptors that detect temperature, pressure, and pain. The PNS splits into two main crews: the autonomic nervous system, which runs the behind‑the‑scenes processes, and the somatic nervous system, which handles the actions you choose to perform. Together, they cover all your senses—touch, smell, sight—as well as every movement, whether you’re deliberately reaching for a coffee mug or your body is silently regulating blood pressure.

3 Autonomic Nervous System

The autonomic nervous system (ANS) is the invisible bridge linking your brain to the majority of your internal organs—heart, lungs, liver, and more. Most of its work happens under the radar, without you needing to think about it. Even functions that seem under your conscious eye, like pupil dilation, are governed by the ANS once the eyes are open.

The ANS further divides into three sub‑systems: the sympathetic (the famed “fight‑or‑flight” response), the parasympathetic (the “rest‑and‑digest” side), and the enteric system (the gut’s own nervous network). The sympathetic branch cranks up heart rate, blood pressure, sweating, digestion, and even urination when you’re under stress. The parasympathetic does the opposite, calming the heart, relaxing airways, and promoting digestion when you’re at ease.

While the theory sounds straightforward, the real‑world coordination is a symphony of signals keeping you alive and functional. Take the enteric system, for instance: it kicks off digestion the moment you taste food, prompting salivation, then orchestrates a cascade of muscle contractions that move food through the stomach and intestines—much like an assembly line in a factory.

A star player in the ANS is the vagus nerve, a massive bundle of roughly 100,000 fibers that shuttles information between the brainstem and organs. This nerve influences digestion, heart rate, breathing, blood pressure, skin sensations, urination, speech, immune responses, and even taste. It taps into about 37 different sensory neuron types, sensing pressure, toxins, nutrients, and stretch, and relays this data to brain regions that handle memory, emotion, and self‑awareness. In short, these “automatic” processes are far more intertwined with our conscious mind than you might think.

2 Somatic Nervous System

The somatic nervous system (SNS) is the part you interact with daily. While the autonomic system runs behind the curtains, the somatic system is the spotlight on stage—everything you consciously decide to move or feel. Walking, scrolling through your phone, waving hello—these are all somatic actions.

Your body houses ten cranial nerves sprouting from the brainstem, which control most head movements, plus 31 pairs of spinal nerves and 12 pairs of cranial nerves that together manage the muscles of your arms, legs, torso, and face. All voluntary movements, even reflexes, are coordinated through this network, translating your intentions into actual motion.

1 Can You Consciously Control Autonomic Functions?

Why does the somatic system answer to you, while the autonomic system seems to ignore your commands? The answer lies in evolutionary design: the body delegated life‑supporting tasks to an automatic pilot so you could focus mental energy on more complex problems. Yet, humans have discovered clever ways to peek behind that curtain.

Holding your breath is a classic example of conscious influence over an automatic rhythm. Meditation practitioners can deliberately slow their heart rate, and some monks have been shown to raise the temperature of their fingers by more than 8 °C (over 46 °F) through focused practice. Wim Hof, the “Iceman,” can intentionally trigger his sympathetic nervous system, releasing epinephrine and dampening immune responses to survive extreme cold—an ability that isn’t genetic but trainable.

Biofeedback technology offers a modern shortcut. Sensors track breathing, heart rate, and muscle tension in real time, displaying the data on a screen. When a participant sees a spike in heart rate during a painful stimulus, they can consciously relax, slowing their pulse and easing tension. This method has helped people manage conditions like diabetes—lowering blood glucose—and ADHD, by teaching them to regulate physiological responses.

Even something as simple as voluntarily producing goosebumps—a reflex usually reserved for cold or fear—has been demonstrated with focused attention. While mastering such feats often requires extensive meditation or training, everyday techniques can grant modest control. Deep, deliberate breathing, systematic muscle relaxation, and vivid imagination (think of a calm, happy place) can shift the balance from sympathetic “fight‑or‑flight” to parasympathetic “rest‑and‑digest.”

A practical breathing routine might look like this: inhale slowly through the nose, hold for five seconds, then exhale through the mouth, pausing ten seconds before the next breath. For muscle relaxation, tense a group of muscles—say, your shoulders—for five seconds, then release for ten, moving through each major region. Pair these with a mental visualization of a serene scene, and you’ll notice a gentle dip in heart rate and a calmer mind.

Full mastery over autonomic functions isn’t realistic—or necessarily desirable. Forgetting to salivate or to urinate would be disastrous. However, with dedication, you can nudge these processes in beneficial directions, improving health, performance, and overall wellbeing.

The human body is a marvel of evolutionary engineering, and these 10 evolutionary advantages reveal why seemingly odd functions have stuck around.

10 Evolutionary Advantages: An Overview

10 Depression

While many people tend to equate just having a bad day with depression, it’s really not the same. The statistics speak for themselves; about 300 million people worldwide suffer from depression, about 800,000 die of suicides, and a vast number of the rest have difficulty functioning as a consistent part of their lives, proving that it’s a serious problem. For all the ways depression hampers life on Earth, it’s hard to imagine how it survived evolution.

According to many scientists, though, it makes perfect sense. Researchers found a correlation between the genes that carry over with depression and those that help protect the body from pathogens that could harm us, which could explain why it carried over to the modern age. Not just that, but the symptoms associated with depression—like social withdrawal and exhaustion—also helped the body reduce the chances of catching a particularly nasty disease by partially shutting down, which would make perfect sense in the pathogen‑ridden, prone‑to‑disease environment that was our early history.

9 Weak Feet

Looking at our feet, we can’t help but think that something may have gone very wrong for them to be the way they are. Think about it; the human foot has 26 bones and is able to twist and turn like most other body parts can’t, though the thing is that it really doesn’t need to. All it needs to do is be sturdy and provide support to the frame while walking, but because of its intricate build, we regularly twist and and mess it up, something it shouldn’t even have the mechanism to do. So what gives?

Bipedalism. Yup, our ability to walk on two feet didn’t just free our hands to make tools and conquer the world, it also took away our feet’s ability to act as secondary limbs, almost as capable as hands in providing us with the agility and maneuverability to navigate our four‑legged lifestyles. While we don’t need all those bones and muscles anymore, evolution just decided to let them stay as they weren’t exactly doing much harm, except for setting ourselves up for regular instances of ankle‑twisting and sprains.

8 Pubic Hair

One of the most enduring mysteries of human evolution, pubic hair really doesn’t make sense. While we know it has something to do with testosterone and estrogen—i.e. hormones related to sexuality—as it only shows up during puberty, we really have no idea why it exists. Not just that, but most of us actively take steps to get rid of it as a part of our grooming routines, meaning that it doesn’t just not make sense but is also unwanted. How did evolution let something like that slip by?

According to some scientists, there are perfectly good reasons for it. For one, because pubic hair shows up during puberty, it signals sexual maturity and also helps trap crucial pheromones that could potentially attract a mate. It makes sense, as in the pre‑clothes era, pubic hair would stand out on an otherwise hairless body, telling whoever’s looking that you’re ready for business.

Another theory suggests that it’s there to reduce friction while having sex, as skin rubbing against other people’s skin may have led us to develop unwanted rashes and other irritating skin allergies that would hamper our chances at getting more sexual partners.

7 Nails On Chalkboard

Ever heard the sound of nails scratching on the chalkboard and felt like someone was out to rip your head apart? Humans are almost unanimously averse to sounds similar to it, like that of a sharp stone on glass, chalk on slate, or a marker on a whiteboard. Evolutionarily speaking, how our bodies react to them doesn’t make a lot of sense—unless our hunter‑gatherer history had a lot of whiteboards or slates, these sounds shouldn’t make us feel anything at all.

According to scientists, though, there are some perfectly good explanations for it. For one, the frequency range these sounds fall in, 2,000–5,000 hertz, also contains frequencies similar to that of a crying baby or a screaming person, which indicates that we developed these reactions as a defense mechanism against something dangerous approaching in our wild hunter‑gatherer days. Another study found that the part of the brain that deals with sound engages with the part that processes negative emotions as soon as any of these sounds are heard. The activity between the two regions also notched up as the sounds got more severe, proving that even though we have no need for this reflex reaction anymore, it made perfect sense back then.

6 Wisdom Teeth

Most people who have teeth—which is just about everyone—have had to come to terms with the painful experience of their wisdom tooth or teeth (as it’s different for everyone) growing out at least once in their life. For those who haven’t, we congratulate you for your luck, but for the other unlucky ones, it’s not the best of experiences. It’s especially bad because they serve seemingly no purpose whatsoever and only end up adding more things in our mouth that could get infected with cavities or such later in life. Most people get them taken out before that happens, but have you ever wondered why they even exist?

The answer is diet. In the old days, our diet comprised all kinds of stuff, like leaves, raw meat, and branches, so our jaw used to be much bigger than what we have today. The wisdom teeth helped us manage our wildly diverse diet, and the bigger jaw made room for the extra set of teeth. Through the years, though, the jaw shrank to accommodate more . . . civilized eating habits, though the wisdom teeth never got the memo. That’s the reason most of us will make at least one visit in our life to a dentist to deal with a wisdom tooth, and you’ve got our ancestors’ way of eating to thank for it.

5 Dangling Testicles

The male reproductive system isn’t as complicated as that of the female, though one part of it has had scientists scratching their heads ever since they started thinking about it. Why do the testicles hang outside like that, given that they’re the most important organs on the list of “things evolution should have protected?” Most animals don’t have it the same, and the ones who do are also our immediate cousins or ancestors (aka mammals). At what point in our evolutionary tree did we decide that putting the sperm in an unprotected sack outside the body was a good idea?

Many theories exist, some of them more convincing than the others. For one, some believe that it’s due to the “handicapping principle,” which suggests that potential mates find the fact that someone who can survive with such a huge evolutionary disadvantage must be someone to definitely mate with, though we feel that may not be it. Another one, which makes much more sense, argues that the reason is protection. Testicles are only found to be outside in the mammals that do a lot of running and exertion—stuff that could cause abdominal pressure and a threat to sperm—so it seems more like an evolutionary mechanism to protect them by keeping them outside, which made more room for all the fun running from the predators we used to do in our early days.

4 Tickling

When it comes to weird body functions, tickling has got to be pretty high on the list. While scientists don’t yet understand the kind of laughter due to tickling, they understand that it shouldn’t be a function. There have been times in history it has been a downright disadvantage, too, like those times when medieval warriors were reported to have tickle‑tortured victims to death. It doesn’t seem to serve any purpose, and yet evolution wasn’t able to “take care of it” through the years.

According to some researchers, it isn’t that weird of a function. You see, the body parts most sensitive to tickling are also the ones most exposed in combat. They theorize that tickling our children was our involuntary way of teaching them how to protect their most vital organs, as the response to tickling among most of us is still defending the body.

3 Fainting At The Sight Of Blood

This one may not be as commonly occurring, but it still happens enough that it raises some pretty big how‑did‑this‑survive‑evolution alarms. Many people are known to faint at the sight of blood, and thinking of it in evolutionary terms, that should have strictly been a no‑no back in our violent early days. Think about it; what benefit could lying down unconscious have in a pitched battle where blood is flowing everywhere? If anything, our brains should get more alert to actively react to danger in those situations. So why don’t they?

It actually makes perfect sense, if you consider the things that go on in the body at the time of that fainting. It even has a medical name—vasovagal syncope—which refers to fainting at extreme triggers, like the sight of blood or trauma. When the body does that, it lowers the blood pressure and generally deactivates itself so that all the resources can go to keeping the brain alive. Moreover, if you’re also bleeding from the threat that made you see the blood in the first place, the body’s slowed functions can decelerate that blood loss, acting as a safety mechanism for you to stay alive longer.

2 Acne

Most people who go through adolescence experience acne. Its effects can be debilitating for some, though they’ve got to realize that they’re not alone. Not only kids but a significant number of adults also exhibit acne, and we just cannot imagine how blobs of red matter on the face could have any evolutionary benefit. In fact, it should have been actively stubbed out by natural selection, suggesting that we got lazy on this one.

According to scientists, though, it isn’t as weird. A lot of blame for acne can be attributed to the evolutionary decision to go hairless. While we lost our fur pretty hastily, we couldn’t get rid of the glands just underneath the surface of the skin—the sebaceous glands—as fast. They served a function back then, which is to oil the fur and keep it . . . furry. Now that there’s no fur, those oils just clog up our face and cause acne. Another theory suggests that it’s an indicator of whether someone is adult enough to have a family, which we could get behind, too.

1 Colorblindness

When it comes to common and weird disorders that are surprisingly prevalent in all populations, colorblindness takes the cake. It’s also pretty weird from an evolutionary perspective; why would an inability to recognize a venomous snake from a tree branch have survived natural selection? Its distribution is also unevenly spread among men and women, deepening the mystery. Compared to the one in 12 men who have it, one in 200 women suffer from colorblindness. It’s also one of the few anomalies on this list we can certainly say survived evolution, as the leading cause of colorblindness is hereditary.

While we don’t intuitively think it’s a good thing, colorblindness may actually have been a definite advantage in some situations. The condition frees the individual from seeing the colors in favor of patterns, and that would have given them an edge over their less colorblind peers in spotting camouflaged predators. In fact, colorblind forces were used in World War II to spot camouflaged positions to great success.

In the animal kingdom, there is no shortage of odd bodily functions to keep you wondering what on Earth Mother Nature was thinking. The list below highlights 10 creatures really displaying bizarre physiology that makes us both marvel and cringe. We share some basics with our animal friends, but the ways they move, eat, and communicate can be wildly different.

10 creatures really: Bizarre Body Functions

10 Chinese Softshell Turtle

Humans usually keep waste production tidy, but the Chinese softshell turtle throws that rule out the window by urinating straight from its mouth. This amphibious oddball actually excretes urea via its oral cavity while submerged, a habit that would make most people blush.

These turtles inhabit fresh waterways, where they dip their heads underwater to release the waste. If they find themselves on dry land, they’ll seek out any puddle or shallow pool, dunk their heads in, and finish the job without missing a beat.

Despite this quirky habit, the Chinese softshell turtle remains highly prized across Asia for its meat and use in traditional remedies, a demand that has pushed the species toward vulnerability in the wild.

9 Sea Spider

At first glance, the sea spider looks like a handful of spindly legs glued to a tiny, toothpick‑like torso. Its skeletal structure is so reduced that nature had to get creative to keep this creature alive.

Instead of a conventional heart‑driven circulatory system, a sea spider’s blood courses through a sprawling gut that permeates the entire body, acting as a primitive pump. Adding to the oddity, it lacks a respiratory system; oxygen diffuses directly through the thin walls of its legs.

Reproduction is equally unusual: the legs double as reproductive organs. Females grow eggs inside their thighs and release them through specialized pores, while males scoop up the fertilized eggs with their own leg‑based pores and carry them around until they hatch.

8 Gardiner’s Frog

Measuring roughly a third of a human fingernail, Gardiner’s frog possesses a startling ability: it hears through its mouth. Researchers in 2013 discovered that sound waves vibrate a cavity inside the frog’s oral cavity, sending auditory signals straight to its brain.

Previously thought to be deaf because it lacks a middle ear and eardrum, the frog was tested by recording its calls and playing them back to a separate group. The frogs responded, prompting scientists to simulate the head’s anatomy and confirm that the mouth cavity vibrated like a makeshift eardrum at the same frequency as the calls.

This tiny amphibian is endemic to the Seychelles and currently faces endangerment due to wildfires, invasive species, and human encroachment, making its unique hearing all the more precious.

7 Shark Electroreception

Electroreception is a super‑sense that lets animals detect the electric fields emitted by every living creature. While many fish and amphibians possess this ability, sharks have honed it to an almost supernatural level.

In water, a shark can sense voltage changes as tiny as a millionth of a volt. This acute perception helps them locate hidden prey and avoid potential threats, essentially giving them a built‑in radar system.

The sensory organs responsible are called ampullae of Lorenzini—jelly‑filled pores dotting the shark’s skin. Each pore contains an ampulla; electric currents travel through the jelly, across the ampulla surface, and are transmitted to the shark’s brain for processing.

6 Fruit Flies Taste With Their Whole Body

Imagine savoring an ice‑cream sundae by slathering it over your entire body. That’s essentially how fruit flies experience taste: they have receptors scattered across their legs, wings, proboscis, and even the ovipositor used for laying eggs.

Although fruit flies don’t discriminate between complex flavors like humans, they can tell sweet from bitter. The receptors on their bristles relay this information to a brain that maps both the taste’s location and its quality, deciding whether the food is safe to ingest.

Other insects share this distributed tasting system—butterflies and houseflies sample with their feet, while honeybees and certain wasps use their antennae to taste the world around them.

5 The Clear‑Blooded Fish Of The Deep

Deep in the frigid Southern Ocean lives the ocellated icefish, a marvel of cold‑adapted evolution. Its heart is roughly five times larger than that of a typical fish, pumping vigorously to circulate blood through its icy habitat.

What truly sets the icefish apart is its lack of hemoglobin—the red protein that normally carries oxygen and gives blood its color. As a result, its blood is completely transparent, resembling the clear fluid of a sci‑fi alien creature.

The surrounding water is so cold that the fish’s plasma can dissolve enough dissolved oxygen to meet its metabolic needs, even without hemoglobin. This adaptation shows how life can thrive in extreme, frozen environments.

4 Elephant Stomping

Scaling up to the massive elephant, we find a communication system that goes well beyond trumpeting. Elephants also flap their large, flag‑like ears and produce low‑frequency rumbles between 10 and 40 Hz—sounds too deep for human ears to perceive.

These subsonic vibrations travel through the ground and are detected via bone conduction, specialized middle ears, and ultra‑sensitive pads on their feet and trunks. Researchers call this seismic communication, allowing elephants to locate the source of a rumble, assess danger, and coordinate movements across great distances.

3 Fish With Creepy Flashlights For Eyes

In the abyss where sunlight never reaches, the deep‑sea dragonfish has evolved a startling visual trick: red light‑emitting organs beneath its eyes. Coupled with razor‑sharp, needle‑like teeth, this creates a terrifying predator.

The dragonfish’s eyes are tuned to the reddish‑orange wavelength, a rarity in the deep sea where blue light dominates because it penetrates water most effectively. By emitting red light, the fish can illuminate prey without alerting other organisms that can only see blue.

Since only the dragonfish can both see and produce red light, it uses this private illumination to signal conspecifics and to spotlight unsuspecting prey, effectively turning the darkness into a personal hunting spotlight.

2 The Guitarfish’s Retractable Eyes

The giant guitarfish, resembling a hybrid of a manta ray and a shark, boasts an eye‑retraction mechanism that lets it pull its eyeballs up to 3.8 cm (about 1.5 in) into its head, protecting them while it forages along sandy ocean floors.

Instead of eyelids, specialized muscles draw the eyes back into a recessed socket, shielding them from debris and potential predators. This adaptation is surprisingly widespread: many frogs can retract their eyes, and several mammals—including dogs, cats, and pigs—can draw their eyes inward as well.

This ocular flexibility underscores the diverse ways evolution solves the problem of eye protection across very different animal lineages.

1 Tentacled Snake

Snakes are already an odd bunch, but the tentacled snake adds another layer of peculiarity with its pair of sensitive, whisker‑like tentacles. Found in the slow‑moving waters of Thailand and Vietnam, this snake buries itself in mud during the dry season, waiting for the rains to return.

These tentacles are hyper‑sensitive mechanoreceptors that can detect the slightest water movements, allowing the snake to locate and ambush fish with uncanny precision.

Researchers have confirmed that the tentacles act as finely tuned sensors, picking up minute vibrations that other predators would miss, giving the snake a distinct hunting advantage.

Tiffany is a freelance writer from Southern California now living in Ghana, West Africa. She loves her work and is fascinated by nature, pop science, and stories of human endurance. She can most often be found reading sci‑fi novels, hanging out on the beach, or indulging in something that has chocolate in it.