The reason I see and hear what I see and hear
Sometimes asking God for a reason for something is like asking Him why the sky is blue. There is a complex, scientific reason for it, Claire, but most children, including you, are content with knowing it is blue because it is — Susan Meissner (Why the Sky Is Blue)
In the previous post I discussed how my senses can only perceive a small fraction of what exists. I can only see only 0.0035% of the electromagnetic spectrum between 380 nanometers (nm) (violet) to about 750 nanometers (nm) (red) and can hear compression (or longitudinal) waves that travel through the air and have frequency between 20Hz to 20,000 Hz. My range of hearing and vision being limited does not mean that there are no electromagnetic and compression waves beyond the limits of my perception. It just means that anything happening out there which falls outside the range of my sensory physiology does not get registered.
Right now, there are worlds beyond the reach of my perception of which I am not aware.
I am oblivious to much that goes around me. I am continuously flooded by electromagnetic waves to which I am not aware. Similarly, there are sound waves continuously passing by, wavelengths of which are beyond my auditory capabilities. The same sound waves, however, are picked up by the dogs taking their evening stroll with their owners on the sidewalk and occasionally their ears perk up as if they are listening to some melodious symphony that is not accessible to me.
Why is it that I can see and hear only a fraction of what is going on out there? It is not by random chance that I, as part of the human race, was blessed with this sensory range, perhaps when the world was created. Is there someone out there divvying up frequencies of spectrums like the FCC does?
The reason for my physiology being what it is has an explanation that traces back to the environment in which my ancestors, and more broadly, life on Earth, evolved.
The BLUF (Bottom Line Up Front) is that the range of wavelengths to which our vision and auditory physiology is sensitive is the result of an interplay between environmental conditions and the principles of natural selection, which work to increase our chances for survival and reproduction.
To understand the range of the electromagnetic spectrum I can perceive, the starting point is the radiation that the Sun emits. For every living thing on Earth that requires energy to maintain its biological functions, the source of that energy, directly or indirectly, is the Sun.
Plants, through photosynthesis, convert the Sun’s energy into various nutrients (such as glucose) and byproducts (like oxygen). They accomplish this remarkable transformation using water from their roots, carbon dioxide from the atmosphere, and light energy from the Sun. For my own existence, I depend on the nutrients produced by plants; thus, the origin of my energy source also traces back to the Sun.
The intensity of the Sun’s electromagnetic spectrum is concentrated within a range from about 200 nm (nanometers) (ultraviolet) to about 2000 nm (infrared). It also happens that at the top of the atmosphere, the spectral irradiance of the radiation emitted by the Sun peaks at about 400 nm (violet-to-blue). Additionally, the gaseous composition of Earth’s atmosphere allows a majority of the radiation emitted by the Sun, between 200–750 nm, to pass through. Conversely, radiation in the infrared frequency is largely absorbed by the water vapor in the atmosphere.
The bottom line is that, with the Sun’s radiation being the ultimate source of energy and its spectral irradiance peaking around 400 nm — declining rapidly on the ultraviolet side and tapering more gradually on the red side (but being absorbed in the atmosphere) — it is unsurprising that the majority of life forms on Earth have evolved to capitalize on this specific environmental condition.
This is why the physiology of my eyes has evolved to perceive what we call the visible spectrum (the use of the word visible is not surprising and is self-referential because I am bound by the limits of the language I use to communicate. What else would I call it?).
What about the physiology of my ears? The story there is no different.
Sound waves are compression waves that travel through the air. Their speed and other characteristics, such as how far sound can travel without losing its energy, depend on the air’s density. My auditory range has adapted to the frequencies of sounds most relevant for communication and environmental awareness, thereby increasing the prospects of my survival and reproduction.
The frequency of sound that can be efficiently transmitted is influenced by the medium’s properties through which the wave is traveling, including its density and pressure. The human ear has evolved to be most sensitive to the range of frequencies that travel best under the atmospheric conditions at Earth’s surface.
The frequencies within the human auditory range are those that can travel through the air easily and are more likely to be associated with sounds that have been important for our survival. The process of natural selection has guided human (and other animals’) hearing to adapt to the typical conditions of Earth’s atmosphere, where the density and pressure support the propagation of sound waves most efficiently within the 20Hz to 20,000Hz range.
Thus, it is no coincidence that my eyes and hearing are attuned to seeing and hearing what they are. In the environment where my ancestors lived and the overall biology on Earth evolved, these are the features that increased the chances for survival and reproduction. Attempts to utilize alternative seeing and hearing strategies either did not progress far along the evolutionary path or became relegated to specialized niches (for example, bats using echolocation).
Ultimately, the principles of natural selection, working within the constraints of the environment where the game of survival and reproduction is played, are the invisible forces that have shaped the physiology of my senses.
In some ways, natural selection could be considered a godlike force making me most adept to where I live.
Ciao.
