“One of the most neglected areas in the philosophy of perception concerns animal senses. It is surprising how many philosophers write about perception in the apparent belief that humans are the only perceivers in the world. Human senses evolved through the natural process as other animal senses, so there is no reason to regard human senses as special, or better than other animal senses.” ― Rochelle Forrester, author

By DR. CAMERON BARROWS

Umwelt, a German word for environment, denoting an organism’s unique sensory world

A species’ umwelt, or sensory world includes its vision, hearing, taste, sense of smell, sense of touch, and sense of pain. Together these senses dictate how organisms perceive and interact with their environment and each other. Until just a few years ago, the default assumption was that in general other species’ vision, hearing, taste, and smell was basically much like our own. After all, all species live on the same planet, breathe the same air, and experience much the same temperatures. The main separation was a belief that some animals, such as fish and insects, do not feel pain. It turns out that all those assumptions have been turned upside down.

The first challenge in answering this kind of question is that we can’t just ask a lizard or a woodpecker or an elephant, or your family’s pet dog or cat or goldfish what they see or smell or hear. Let’s start with vision. Anatomically, eyes include sets of neurons called rods and cones. Rods detect brightness, and cones detect color of different wavelengths, with each cone detecting a particular wavelength or color. The density and types of these neurons determine visual acuity and color perception. Humans have three types of cones, and through those cones we can see the colors of the rainbow. Dogs have just two types of cones and probably can only see yellows and shades of gray. Birds and insects have more types of cones than humans, with some seeing into the ultraviolet wavelengths. It turns out that a rainbow has far more colors than humans can see.

Flowers that depend on birds or insects for their pollination often have color patterns in the ultraviolet range aimed at attracting those pollinators, patterns we never see without added sensors. Some arthropods, reptiles and fish can see into the infrared range, seeing the heat signatures of both potential prey and possible predators. In the case of infrared wavelengths, animals sometimes “see” with more than just their eyes. Ticks “see” infrared with sensors on their legs, alerting them to the approach of a potential blood meal. Some snakes, including rattlesnakes, have what are called Jacobsen’s organs, paired sensors on the front of their head that allow them to “see” the infrared signature of a small mouse even when there is a moonless, starless (cloudy) night sky.

When it comes to seeing the spectrum of color wavelengths that exist in nature, our eyes are nothing special. However, when it comes to visual acuity, only birds of prey surpass our ability to distinguish objects at great distances. We, along with birds of prey and other predators, have binocular vision (forward-facing eyes) that allows us to have depth perception. Most animals’ eyes are placed more to the sides of their heads giving them a wider view (better for detecting an approaching predator) but at the expense of poor to non-existent depth perception. Some, like chameleons, have eyes on rotating “turrets” so they can look forward and backward at the same time. I have often wondered how that appears in their brain. Is it akin to a split vision screen? Or does the chameleon’s brain switch between eyes, until one eye detects a potential prey item like a grasshopper, or a predator, or a possible mate? Then, both turrets, and so both eyes, focus on that object of interest, giving the chameleon binocular vision and depth perception for aiming their extraordinarily long and sticky tongue that they fling out to snare a prey item.

Our sense of smell allows us to assess the quality, and safety, of the food we eat. We seem especially tuned to odors associated with spoiled foods, clearly an adaptation for avoiding potentially harmful bacteria. Still our smell umwelt is nothing special. An elephant or dog’s sense of smell allows them to assess those who have proceeded them down a path, identifying the species, and in some cases their sex, their health, their levels of anxiety, and their estrous cycle, detecting the molecules that someone or something had shed sometimes days after that individual had passed by. Imagine the levels of human discourse we would have if we had the olfaction capacity of elephants or dogs. We would never have to ask: How are you feeling? Are you kidding me? After a single whiff, we would already know.  

Noses aren’t the only organs for smelling. Butterflies and moths smell using sensors on their feet, “smelling” the species of plant they have landed on to determining if it is an appropriate place to lay eggs, sensing whether the proper nutrition and chemical cocktail are present to nourish and protect her caterpillars when they hatch. Snakes and some lizards (Komodo dragons and other varanid lizards) smell by tasting the air with their forked tongues. When they are tracking a potential prey animal they can follow to where their next meal is hiding by which fork of their tongue detected the most of their quarry’s molecules, and then always moving toward that higher molecule density.

The umwelt of bats, whales, dolphins, and porpoises is in part defined by their use of ultrasonic sonar. Sending out pulses of sound and then listening to the echo, bats can detect and capture insects as small as mosquitos. Cetaceans hunt and communicate with each other using their sonar. Given the high intelligence of cetaceans, I wonder if that communication is in the form of images like a sonogram, or whether the various ultrasonic clicks they use are something akin to a language, or both.

Finally, there has been speculation about whether non-human animals feel pain or fear as we do. The research is sparse, given the ethical problems associated with subjecting animals to pain or fear. Past beliefs indicated that fish and invertebrates probably do not have these senses. Objectively, pain and fear and the fear of pain are important senses aimed at keeping us and other creatures from situations that could result in shortening our lifespans. Lacking those senses would allow such creatures to take chances or be put into situations that could reduce their chances of contributing their genes to future generations. None of the research that has addressed this question has provided any support for the contention that some creatures might be immune to pain or fear. Pain and fear may be a more universal component of the umwelt of all species, uniting us all more than any of our other senses.

If you are interested in a deeper dive into these topics, I recommend the book, “An Immense World,” by Ed Yong.

Nullius in verba – Go outside, tip your hat to a chuckwalla (and a cactus), and think like a mountain