Ed Yong introduces us to the topic of his book, An Immense World (1), by inviting us into an imaginary gymnasium populated by a menagerie of animals who perceive their environment in different ways because they have different sensory mechanisms. The elephant is waving its trunk in the air like a periscope, using its strongest sense to smell and taste the room. The mosquito is also relying on its sense of smell to find the source of carbon dioxide that its prey emits as it breathes. The rattlesnake detects the smell of the mouse by flicking its smelling and tasting tongue into the air. The bat finds the spider ensconced in its web by using echolocation sonar to locate it. The human in the room can’t hear the sonar clicks emitted by the bat because the sound is beyond her limited range of hearing. When Yong turns the lights off in the gym, different senses are deployed by different animals. Those who rely on light to perceive the room suddenly lose much information about what’s happening in the room, while other animals suddenly have an advantage.
Yong wants his readers to know about the extraordinary diversity of sensory perception in the animal kingdom. He asks us to appreciate that diversity while resisting the temptation to compare them to the capabilities of humans: “…this is a book not about superiority, but about diversity.” The dominance of one sense over another is usually logical in the context of the environment in which the animal lives. For example, animals that live in a dark environment or are active only at night need a different suite of senses than animals that live above ground and are active only in daylight. In his concluding chapter, Yong urges us to understand how animals perceive the world so that we can mitigate the impacts of human activities on the animals with whom we share the world.
The chemical senses: smell and taste
Yong begins with our weakest senses: smell and taste. Anyone who has walked a dog knows the dog senses the world primarily through its nose. Although dogs can be distracted by a moving squirrel or another dog, they are not there to enjoy the view because they are walking with their nose to the ground. Their nose is informing them of who has been there and many of the characteristics of that animal, such as species and gender. They are also searching for food and their taste in food is radically different from our own. Goose poop is as attractive as the treats we carry to distract them from the squirrels, suggesting subjectivity in the perception of smells and tastes. I doubt that humans would find either the odor or the taste of goose poop appealing and opinions of odors and tastes vary widely among humans whose sensory perception of odor and taste are equally astute.
Our noses are structurally similar to the dog’s nose, but dogs have “more extensive olfactory epithelium, dozens of times more neurons in that epithelium, almost twice as many kinds of olfactory receptors, and a larger olfactory bulb.” Consequently, they can be trained to detect “bombs, drugs, landmines, missing people, bodies, smuggled cash, truffles, invasive weeds, agricultural diseases, low blood sugar, bedbugs, oil pipeline leaks, and tumors.”
“The lives of elephants are dominated by smell.” Their nose is their most conspicuous feature and it is in constant motion to inform the elephant of where it is, where its companions and family members are, and where it is going. Their nose, which both smells and tastes, helps them find water and food.
Our comprehension of what animals smell is limited partly by our own limited sense of smell. The myth that birds can’t smell originated by James Audubon in the 19th Century was not dispelled by research until the 1960s. Yong reports many other errors of scientists in reporting the sensory capabilities of animals. He suspects that many of those errors are yet to be corrected.
The ability to detect and identify odors in the environment are important to many animals because they enable animals to both avoid predators and find prey to eat. The odors that animals emit as pheromones help many animals find and attract their mates. Humans also emit pheromones in sweat and other secretions and they are said to play a role in choosing our mates, although we are rarely conscious of their role in our choices.
Vision and Color
The diversity of the tools of vision in the animal kingdom is remarkable. Our two symmetrical, frontal-facing eyes are not the norm: “eyes can come in eights or hundreds…they can be the size of soccer balls or the size of a amoeba’s nucleus…they can be made of protein or rock…they can appear on mouths, arms, and armor…they can accomplish all of the tasks our eyes can perform, or just a few.” Each variation produces a different visual perception from seeing crisp detail to blurry blotches of light and dark, from seeing in the dark to blindness in bright daylight, from slow-motion snap-shots to high-speed images of motion, from a narrow view of what’s in front of the animal to a 360⁰ view.
Our vision is one of our strongest senses, yet many animals are able to see “better” than we can. (I put “better” in quotes because like everything in the natural world there are pros and cons to every animal’s suite of senses and the judgment depends on the specific environment in which the animal lives.) We can see three colors (red, green, and blue) and all combinations of those colors, but many animals can see another spectrum of color called ultraviolet (commonly abbreviated UV light), adding many colors that we can’t see. Many animals see only gradations of black and white. Color is a function of the eye in coordination with the brain, rather than inherent in the object we perceive.
Birds and bees undoubtedly benefit from their ability to see a full spectrum of color to find and identify plants they need for food. Before the advent of molecular analysis, scientists speculated that birds evolved the ability to see color after plants produced colorful flowers. Now that we know more about the evolutionary sequence of events, we know that plants produced colorful flowers after birds evolved their perception of color. Plants benefit from the visits of birds and bees for pollination services and to spread their seeds to expand their range. Natural selection gave plants with colorful flowers the edge over colorless flowers.
Dogs and many other animals can see only two colors: blue and yellow. About 8% of men and .5% of women are red-green color blind. Their perception of color is the same as dogs. This picture from An Immense World shows the difference between perceiving two compared to three colors:
As late as the 1980s many scientists believed that dogs are color blind. Although the knowledge that dogs can perceive two colors has been known by scientists for some time, many people still don’t know that. This is an ad for colored buttons that are sold to train dogs how to communicate with their guardians. This product is based on the mistaken assumption that dogs can see the same colors that most humans can see.
The consequences of our ignorance of the perceptions of animals
When considering the importance of understanding the perception of animals, there is more at stake than selling products that are based on our knowledge of what animals perceive. The last chapter of Yong’s book is asking us to understand how animals navigate the world so that we can keep them in mind as we continue to alter the environment for our entertainment and convenience.
In particular, Yong is concerned about light and noise pollution that are disruptive to the animal kingdom. When we illuminate our world with 24-hours of light we deprive many animals of the darkness they need to migrate and hunt. When the twin-towers in New York City were destroyed in 2001, they were replaced by a memorial that casts a laser light into the sky to the height of the missing twin-towers on 9/11. The timing is unfortunate for the birds that migrate at that time of year. They become “trapped” in the laser light and are often killed when their navigation is confused by the light. This is just one of many examples of how human activities intrude on the animal kingdom.
Likewise, our activities make so much noise in the environment that we drown out the signals of animals that they need to communicate, hunt, and find their mates.
Unfortunately, Yong misses the opportunity to advocate for reducing the chemical pollution that is equally harmful to animals. The pesticides we spray are masking the chemical cues that enable animals to hunt, avoid their predators, and communicate with their mates and other insects. Professor Ann Rypstra (Miami University, Ohio) gave a presentation to the Beyond Pesticides Forum about this issue in 2021. She said, “the presence of herbicides at non-toxic levels often act as “info-disruptors” when they interfere with the natural flow of information in ways that alter the interactions between and among predators and their prey as well as impacting the landscape for sexual selection.” You can see her presentation HERE.
I have covered a small fraction of the diversity of sensory perception in the animal kingdom. I provide this brief list of some of the topics that I haven’t covered, hoping that you will be inspired to look further into this fascinating topic:
- The perception of sound
- Tactile perception
- The perception of vibrations
- Echolocation: using sonar to find prey and explore the environment
- The use of electric and magnetic fields to perceive the environment and navigate
Humans do not have some of these sensory capabilities, but in many cases we have developed tools that compensate for our limited inherent sensory abilities. Humans have used a compass for over 1,000 years to detect the Earth’s magnetic field to assist navigation. We have learned how to use sonar to emit sounds we cannot hear to locate and explore objects that aren’t visible to us. We have developed night-vision goggles to improve our limited ability to see in darkness. More recently, we have developed microphone equipment to turn the vibrations that insects make into sound we can hear. The sensory capabilities of other animals has alerted us to these opportunities to enhance our sensory capabilities.
An Immense World will give you the full picture. If you want a more detailed summary of the topic than this article provides, I recommend Ed Yong’s article in Atlantic Magazine, available HERE.
- Ed Yong, An Immense World: How animal senses reveal the hidden realms around us, Random House, 2022. Most quotes in this article are from this book unless indicated otherwise.