The Ecology of Humans (13) The Senses

The Senses

The senses deceive from time to time, and it is prudent never to trust wholly those who have deceived us even once. ~ René Descartes

The senses interface an organism to its environment. That interface defines the boundaries of manifestation: what seems real, which mental processing constantly interprets into a mosaic composition moment by moment.

The senses of every species are adapted to abet survival. Human visual receptivity to red is especially acute because this furless ape has a ruddy face which is best read for emotive content by such sensitivity. This sensory ability facilitates social interaction.

The senses foreclose much more than they reveal. We take our perceptions for granted as presenting the “real” world. This is nothing more than a comfortable fiction.

Every organism inhabits a world of its own, inexorably shaped by its sensory input. We know that people receive and value sensory input distinctly.

Sensory perception is a cultural as well as physical act. ~ American psychologist Constance Classen

As each species has its own ranges of receptors, and different emphases on which senses predominate, sensation and perception are also distinctive.

Receptors are organized in a way that reflects the nature of the sensory experience. ~ Israeli neurobiologist Noam Sobel

The senses not only provide input but also act as an unconscious immune system by natural attraction to what is healthy and avoidance of what is not. An animal that cannot tell the difference, or worse, is attracted to what is not healthy, has been forsaken by its own senses and mind.

Each sense has its own organization. The inner ear is set up according to a tonal scale. The receptors in the retina are arranged spatially, to efficiently map visual coordinates. Smell receptors are bunched by how agreeable a scent may be. By contrast, the tongue is not spatially structured in discerning taste. Instead, taste is organized by admixture of 7 distinct flavors.

The senses are inexorably intertwined: experienced in an integrated fashion and may be even be mixed (synesthesia).

The physiology of the senses is also entangled. Though the mechanism is unknown, prolonged exposure to cigarette smoke, even second-hand, can cause hearing loss.


We have been adapted by evolution such that we inhabit a world which represents a tiny fraction of what actually exists. ~ American cognitive scientist Edward Kelly & American cognitive scientist David Presti

Bees, birds, and fish see in the ultraviolet spectrum. Snakes sense infrared. People cannot detect polarized light, which is how bees navigate on a cloudy day.

Bats and the moths they prey upon live and die by ultrasound. Owlet moths have ears on their thorax: tiny tympanic membranes (tympanum) attached to sensing cells, which can hear a bat’s sonar splashes. A moth flies the other way if the sonar sensation is slight. Up close and dangerous, an owlet moth gets jiggy: erratic evasive maneuvers, which lowers the odds of becoming bat bait.

The sonar senses of both bats and dolphins create detailed mental images without light.

Hearing sensitivity replaces sight for nocturnal birds of prey. A barn owl can home in on a mouse in the dark by the mouse’s rustling about, or even just chewing.

Some creatures don’t need ears to hear. Fish have a lateral line organ running down each side of their bodies. These are pressure sensors that pick up pressure oscillations; a way of mentally mapping the surrounding water. Lateral lines are most developed in fish of the deep, or dark caves, where light is lacking. But even well-lit fish with seeing eyes use their lateral line to keep track of what’s around, as a supplement to sight. Blind fish can stay in a school, but those lacking a decent lateral line tend to crash into each other. Many amphibians also have a lateral organ.

Some caterpillars have hairs that can detect a flying wasp up to a half meter away. Cockroaches have cerci hairs that sense the faint air movements of a toad’s tongue as it prepares to lash out, giving a roach time to slip away.

Smell is vital to most animals. Insects notably live in a world of scents.

Female silk moths waft a wide-ranging alluring scent that can be picked up by a male when diluted to as little as 100 molecules per cubic centimeter. A male can locate a female entirely by odor.

Snakes find each other by pheromone trails. Pheromones create a communication complex for house mice, who know the sex, genetic makeup, and social status of others just by their scent.

Dogs can smell substances at a few parts per million: up to 10,000 times more acute than humans can muster. Dogs can smell whether a human has cancer, as cancer cells let off different metabolic wastes than normal cells.

Dogs can even sniff out infections, such as those caused Clostridium difficile. C. difficile bacteria docilely reside in the gut of some people. For others, it opportunistically invades those who dosing themselves with antibiotics, which indiscriminately kill native gut bacteria. C. difficile often mimics flu symptoms, but most seriously causes diarrhea and colon inflammation. Stopping antibiotic treatment is the common cure for a C. difficile infection.

Our sense of smell is better than we are consciously aware of. Females are more attracted to the smell of a man who has a dissimilar immunity complex (MHC) from her. This is part of the diassortative mate preference found in humans: an evolutionary adaptation to maintain a widened gene pool. That withstanding, overall, human mating preference is assortative: toward similarities.

Electrical and magnetic fields are sensory experiences for some species. Duck-billed platypus close their eyes, ears, and nostrils when underwater. They sense their prey using electroreceptors on their bills which can detect the electrical fields generated by muscle movement in the tasty crayfish and shrimp upon which they feed.

Sharks and rays can detect electric field changes as small as 0.005 µV cm–1; far beyond the ability of humans to sense an electric current.

Electric fish tend to live in turbid waters where vision wouldn’t be much use, so they create their own electric fields and sense nearby objects by their conductive characteristics.

Electric fish conduct their social lives by electrical communication. Finding an attractive mate comes as quite a shock.

A wide variety of life – from bacteria to bees and from ducks to dolphins – rely upon Earth’s magnetic field to keep their bearings, using molecules of magnetite for a receptor. Humans subconsciously detect magnetic fields, but the employment of this magnetoreception is not known.

Some senses are craftwork. A spider can detect a disturbance in its web of as little as 1 nanometer. An annoyed spider will attack a tuning fork touching its web.

The intelligence system is keyed to the senses in making sense of the world confronted. Organisms without brains mentally incorporate a variety of sensory input to make decisions and re/act accordingly. Coherent evolution provides the sensory equipment that circumscribes the senses as well as providing the intelligence capacity to make sense of what is sensed.

Perceptual systems are a species-specific adaptation not designed to show reality as it is, but tuned to keep an organism alive. ~ American cognitive psychologist Donald Hoffman

Human vision consumes 1/3rd of the brain’s energy when the eyes are open. It is no wonder that sleeping for 1/3rd of one’s life is required to rejuvenate.

If the native intelligence of all life was equivalent it would scarcely change how organisms respond to everyday events, as the map of the territory is largely defined by the senses.

The senses ultimately serve as the handmaiden to the mind. Mentation can override what is perceived. When confronted with conflicting sensory input, the mind decides which sense to trust.

As you know, the senses can deceive. Deceptions, like all biological processing, are pattern oriented. The body’s immune system rejects foreign matter: “foreign” being a pattern match to what is known and not welcome. Autoimmune diseases are a mismatch between what is being rejected and what should be.

Artificial limbs have a long history of bodily rejection by the immune system. Even though the body metabolizes iron, prosthetics made of the metal are rejected.

In contrast, the body has no need of titanium. It is not an organic element. Without recognition, the body accepts titanium. Osteoblasts – bone-forming cells – readily latch onto titanium as if it were bone. In the United States since 1952, titanium has been the standard for structural replacement parts: from implanted teeth to any appendage where bone has a natural home.