The Evolutionary Puzzle of Human Senses: Why Five?

 

Think of the fact that a deaf person cannot hear. Then, what deafness may we not all possess? What senses do we lack that we cannot see and cannot hear another world all around us? Frank Herbert

Arun Kumar

Arun Kumar+ AI

I have five senses through which I perceive the state of the environment I live in. The basic purpose of the senses is to aid my survival and strive towards having an edge in the evolutionary race and for acquiring resources that are limited.

Having the capacity of stereoscopic vision helps me navigate the environment I live in. It helps me identify food sources and detect potential threats. But now that I have the capacity for vision, it also allows me to enjoy the beauty of a rainbow after the rain that has cooled down a sweltering summer day of August. As the enjoyment vision can bring comes at no added price, I gladly accept that gift.

The senses I have are neither an outcome of the agency of a designer nor are random.

Along the evolutionary path, no one said that thou should have such and such senses and put engineering skills to work.

They are not random either in that I did not evolve to develop a sense that is influenced by minute changes in gravity along the road as I drive from home to work. There was a reason for it.

My senses evolved to be sensitive to the carriers of information that dominate the environment I live in.

My eyes have receptors that are sensitive to electromagnetic radiation, and particularly to the wavelengths that dominate Earth’s environment, courtesy of the Sun.

So, why five? Why not one, two, three or why not six or seven?

In asking this question, a simple fact that I forget is that the entire human population does not have five senses. Around me, there are citizens who may be deaf, or could be blind, or may not have the sense of smell (remember when having COVID-19 robbed us of the sense of smell and taste). In such cases, an entire dimension of their perception of the environment goes missing.

Even if we have five senses, the range or biology of senses can differ from person to person. Some citizens have the vision but lack the biology to differentiate among colors (color blindness). The range of sound waves different people can hear varies from person to person. Some have a sharper perception for taste and smell (sommelier anyone) than others.

As for each of us the perception of the environment and the world around us differs, we do not even know what we miss. Sure, we can read and hear about other’s experiences, but that is no substitute.

Coming down to my single self, the capacity and range of my senses has been changing as I age. When young, I could not stand the taste of certain things, which is no longer the case. The reason I have been told is that my younger self had lots more taste receptors and the explosion of senses I perceived was just overwhelming.

As I get older, slowly I might also lose some capacity related to sense of smell. The thought makes me wonder if the pleasure of wine I perceive now would be the same.

For that matter, what experience a sommelier gets out of wine is much more different than what I do.

Discarding the variations that exist within the citizens of the human race, collectively we have missed some carriers of information that exist in the environment we live in.

Take the example of Earth’s magnetic fields. The Earth’s environment is permeated with a magnetic field that can function as a carrier of information. Some birds use that for navigation. We are oblivious to this possibility.

If we had receptors that were able to perceive Earth’s magnetic field, I wonder what capabilities we might have developed. Would we have developed ‘magnetic music’ to wow our sense of magnetic field? Would have acquired capacity to create wonderful ‘magnetic paintings?’

So, why five?

Having less than five senses when the competition is well adept at using five is easy to argue against — it would be a terrible handicap in the evolutionary race. By now, we would have been extinct.

Having more than five senses would have been beneficial, but natural selection and evolution did not go for developing senses for magnetic or gravitational field. Why?

One reason could be that even though there are carriers of information about the state of the environment beyond what we are sensitive to, the signals are too weak to be discerned and useful.

Another possibility is that incoming information from any more senses than we already have would have overwhelmed the capacity of the brain.

As such, a small three-pound organ that is brain utilizes about 20% of energy we consume.

To keep my biological functions going, the brain is constantly working. Like muscles do, however, it has no capacity to store energy, and therefore, has to constantly generate and utilize energy. Neurons, the cells in the brain, communicate through electrical and chemical signals. This process, especially at synapses (the junctions between neurons), requires a lot of energy to maintain and transmit signals.

I could have developed additional sensory mechanisms but doing so would have overwhelmed the energy requirements of the brain and any added advantage might have negated by additional requirements for energy (which is not free and has to be competed for).

So, here I am. Content with five senses that give me adequate survival advantage. And as a bonus, allow me the pleasure of drinking the glass of red wine that is nestled in my hands.

I may be missing some pleasure that the capacity for sensing magnetic fields might have brought, but I have no way of knowing what those pleasures might have been.

What I do not know, I do not miss (with the exception of my eventual death).

Ciao, and thanks for reading.

How Biological Organisms Evolved Senses to Respond to Their Environment

 

Think of the fact that a deaf person cannot hear. Then, what deafness may we not all possess? What senses do we lack that we cannot see and cannot hear another world all around us? Frank Herbert

Arun Kumar

Arun Kumar + AI

Biological organisms, including you and me, need mechanisms to sense their environment and capture information that is available in various forms. If they do not, they might as well be rocks and stay at one place.

In the context of this discussion, information is bits of facts that can convey characteristics (or properties) about the environment. These facts can enable the assessment of the state of the environment, and in response, can be used to alter behavior.

For a biological organism, the need for gathering information is essential to know, and to adjust according to the properties of the environment they live in. Mechanisms to take in the information are necessary for their survival and for successfully competing for resources that are up for grabs.

Information, therefore, is factoid about the state of the environment at point A where it originates and travels to point B, and along its passage, carries a signature of what was happening at point A where and when it originated.

The transfer of the fact from point A to point B needs to be in some form of carrier that can travel between the two points. Carrier could be waves — electromagnetic waves, gravitational waves, compression waves etc., fields — electric, magnetic etc., medium properties — molecules etc., physical contact — touch etc.

At point A sits the source of information. At point B there is a mechanism that receives the information. The information could be encoded at its sources, and if so, it needs to be appropriately decoded at point B where it is received.

In summary, learning and reacting to the state of the environment requires a modality to carry the information, a source, and a receiver of the information, and possibly, the encoding and decoding of the information.

The environment I live in is permeated with the carriers of environmental information — electromagnetic waves, sound waves, magnetic and electric field, molecules, pressure, temperature. Biological organisms can exploit all these carriers of information to learn about the state of the environment and exploit that information and benefit from it for their survival.

Somehow natural selection by trial and error, and by amplification of chance happenstances, has figured out how to tap into carriers of information that travel through the environment I live in.

My capacity for vision is plugged into electromagnetic radiation as the carrier of information about the state of the environment. My capacity for hearing taps into compression waves. Smell and taste are tuned to either molecules floating in the air or to objects that are put inside my mouth. My sensitivity to touch helps me interact with my environment, perform delicate tasks, and detect harmful stimuli.

The information gathered by my senses is carried to the brain, where based on the memory from similar experiences from the past, is interpreted. If past analogs do not exist, the information is analyzed as a novel experience (and is also stored for later use). Either way, once an interpretation is made, the brain sends a signal back to one of the body organs to react — run if information resulted in an inference of danger, engage if it has a potential for benefit (e.g., a smell for food).

There are also carriers of information about the state of the environment to which I am not sensitive. I never developed senses to that are receptive to the Earth’s magnetic field that aid birds in their navigation,

In certain locales, some classes of carriers are missing and corresponding sensors and receivers have not evolved. Moles and fishes living in dark caves never developed senses that are receptive to electromagnetic radiation. Doing so would be a waste of resources. Instead, they rely on other senses that may be much more sensitive than I.

A curious fact about single cell organisms is that they sense their environment, and direction, is via chemical gradients. Our immune cells figure out the site of infection using the same mechanism — whichever direction there is propensity of signaling proteins (e.g., cytokines) tells the immune cells which way to travel to.

The miracle story in the development of senses is also the fact that none is predetermined.

Development of appropriate senses to get an edge in the war of survival depended upon the environment the biology evolved in. No electromagnetic radiation, well, there is no need for developing sensory organs for vision.

The complementarity of senses and presence of carriers of information is not a story of a hole fitting the puddle, but it is the other way around. A carrier of information exists, and natural selection figures out what senses would be useful (and will enhance the chance of survival).

Another miracle to think about how it all must have started.

As it is not by design, the development along the pathways for senses must have started by chance happenstance. At some point, a proto-organ to sense a carrier, and to benefit from the inferred information, developed. A small bit of evolutionary advantage it gave, via positive feedback, snowballed into the sensory organs I currently possess.

Perhaps, it is the same story for the development of consciousness. Whatever the biological, psychological, cognitive, social markers of consciousness may be, their development may have followed a similar pathway. A nascent capacity for proto-consciousness, a survival advantage associated with it, and positive feedback leading to the capacity of consciousness (that also has the capacity to question itself).

I guess, learning about the development of senses has lessons to also teach us about the development of consciousness.

Ciao, and thanks for reading.

Why Do We Have Senses? Exploring the Evolution and Neuroscience Behind Human Perception

 

Equipped with his five senses, man explores the universe around him and calls the adventure Science — Edwin Hubble

Arun Kumar

Arun Kumar + AI

A just opened bottle of Almos Malbec 2022 is sitting on the table calling me to savor it with all five senses I have. It is not an expensive wine but one that I happen to enjoy. In the world of wine, and in life, which is what matters — things one enjoys get decoupled from their monetary value.

The wine is calling me to pour it in a glass and appreciate seeing its beautiful ruby red color. I heed its calling and pour a serving in a wine glass.

I then raise the glass and clink it against the glass of my drinking companion and hear the familiar ritual of us saying Cheers.

Following the rituals of wine drinking, next I swirl the wine in the glass and bring my nose against its rim to smell its flowery aroma.

Next, I raise the glass, take a sip of the wine, and feel the touch of its smoothness against my tongue.

And finally, I swirl it around in my mouth and savor its taste and while swallowing, close my eyes and enjoy wine’s finish.

The act of drinking wine engages all the sensory capacities I possess.

As the level of the wine approaches the bottom of the glass and the mind and body are getting mellower and sanguine, just like the ruby red wine I swirl in the glass, philosophical musings also start to swirl in my mind. The one that bubbles up to surface is the wonderment as to why do I have senses, and why they are five and not four or six?

Why do I even have senses?

The basic function of the senses is to collect and bring information about the environment in which I exist. This information is interpreted by the brain, and once an inference is drawn, and if deemed necessary, is acted upon.

To survive, I need to sense the environment in which I am functioning. Also, I need to compete against resources available and senses aid in doing that. The more discriminating they are, the better is their utility for my survival and wellbeing.

Without the means to sense the environment I would either be dead on arrival or might as well be a rock.

Take vision. My ability to see in color and perceive depth (stereoscopic vision) helps me navigate the environment I live in. It helps me identify food sources and detect potential threats. Vision is particularly important for me as I rely heavily on visual information to navigate the surroundings.

My ability to detect a wide range of sounds allows me to communicate, share learning and experiences. Hearing also helps me recognize danger and locate resources. For example, hearing enables me to detect a predator or a prey even when they are not visible.

My sense of smell (which is also linked to taste) helps me identify edible and nutritious food while avoiding the ones that are harmful to my cellular functions.

My sensitivity to touch helps me interact with my environment, perform delicate tasks, and detect harmful stimuli like extreme temperatures or sharp objects. This sense is also crucial for physical interaction and manipulation of objects.

And lastly, taste is important for identifying nutritious food and avoiding toxic substances. It is linked with smell, enhancing my ability to enjoy and discern assorted flavors.

In the end, senses definitely did not evolve willy nilly and without a reason. In the hands of natural selection anything seldom does.

For sure, they did not evolve with the aim of drinking wine while watching a beautiful sunset listening to the birds return to their nest and smell the wafting aroma of someone frying onion and prepping for dinner, a smell that makes my taste buds salivate as the cool breeze of evening touches my skin. But having them brings so much joy.

My senses make the environment feel beautiful and sublime. With that thought I lift the glass, take the last sip, and reach out for the bottle to pour another glass.

After all, an open bottle, and wine, is terrible thing to waste.

Ciao, and thanks for reading.

That Snickers Bar

 

The moment it touched
      my lips,
all intentions to be sattvic
      had evaporated
from my thoughts.

The first embrace
      led to another
until all was consumed
      and I lay
in a stupor
      of crazed ecstasy.

It is only in the morning
      when I see the brown wrapper
lying crumpled on the floor
      I ask
how I could have fell
      for its sultry charm?