What’s in it for me? Discover a world hidden to human senses.
If asked to name the senses, most of us might answer with the common five: touch, taste, sight, hearing, and smell.
These are the senses most commonly linked to being human.
But frankly, compared to the rest of the animal kingdom, these five senses barely scratch the surface.
Maybe you’ve heard of birds using the earth’s magnetic field – a sense called magnetoreception – to migrate for the winter.
But were you aware that sea turtles and spiny lobsters also use this sense?
And you’ve almost definitely heard of electric eels – but did you know they can actually generate enough voltage to kill a horse?
But let’s not give all the credit to animals.
Perhaps you’ve heard of dolphins and bats using echolocation – did you know humans are actually capable of it too?
These are just some of the amazing sensory abilities we’ll explore in this Blink to Ed Yong’s An Immense World.
You’ll catch a glimpse of a world yet unknown to humans and discover entirely new ways of making sense of the realms around us.
As we journey through the world of moles that build mental maps using touch, beetles that hunt fires, and fish that generate electric fields, keep your mind (and senses!
) open.
You just might find yourself thinking – and interacting with your environment – in new ways.
Seeing the world: Color and echoes
Most of human society is built largely around our sense of sight.
How we dress, how we get around, how we consume information .
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the list is endless.
And, to be fair, humans do have a sharp sense of sight – at least compared to much of the animal world.
Humans are trichromats, which means we have three different cones in our eyes that specialize in detecting certain wavelengths of light.
By contrast, dogs and horses only have two.
Dogs mostly see shades of gray, yellow, and blue as a result.
Many “color-blind” people are also missing one of the three cones humans usually have, and so they see a smaller range of colors.
Those of us who use three cones to see color can get an idea of how dichromats see the world using picture editing software.
But we can’t imagine what seeing with four cones would be like.
Animals with more than three cones perceive more colors than we can even comprehend.
But they can’t compare those colors, which is how sighted humans build an understanding of what the world looks like around them.
Instead, for animals whose brains don’t compare colors, different wavelengths of light merely spark instinctive responses.
Daphnia water fleas only see flashes of color, not full landscapes.
An ultraviolet light indicates sunshine, so they swim away.
They swim toward the colors green and yellow because those wavelengths indicate food.
These fleas interpret wavelengths of light as just another stimulus prompting their instinctual behaviors.
They simply don’t experience the sense of sight the same way we do.
Another way of “seeing” the world involves a different sense: echolocation.
Animals like bats and dolphins use echolocation to build visual pictures of the world around them.
They produce pulses of ultrasonic sound, then listen to the echoes returned from objects around them.
They vary the length and frequency of these sounds to build clear pictures of their surroundings.
In fact, bats are so good at this that they can snatch flying insects out of the air and navigate through a maze of hanging chains.
Dolphins can recognize two-dimensional pictures of items they’ve previously investigated using sonar.
But this incredible ability isn’t just limited to the animals around us – humans can learn to echolocate too.
Daniel Kish had his eyes removed at the age of 13 months in response to a particularly aggressive form of eye cancer.
As he grew up, he started exploring the world using tongue clicks.
It took him awhile to be able to put words to what he was doing – echolocating.
Now, after decades of practice, Kish can take a walk around the block and tell where houses end, where a yard is versus a driveway, and where trees stand.
He ducks to avoid branches of trees overhanging the sidewalk – branches he senses using echolocation.
By watching dolphins and bats echolocate, we can determine a lot about how the sense works and what its limitations are.
But Kish can tell us how it works for him.
Because his sonar is lower in frequency than bats’, the resolution of what he senses is a little blurry.
Edges aren’t crisp, and objects in front of large backgrounds – like a person standing right against a wall, or a small object on the ground – can be hard to sense.
So he mostly defines objects by their density and texture when using echolocation.
Name an animal that excels at smelling.
Which animal did you pick?
A dog?
An elephant?
Probably not an ant.
Smelly but tasty
But while ants are tiny, they actually have an incredibly sensitive sense of smell.
They leave scent trails for themselves and others to indicate where they’ve found food, to identify each other as members of the same anthill, and to summon their colony members to overwhelm prey with their numbers.
Ants do this with pheromones – chemical signals that are used to communicate within a species.
Ants so thoroughly rely on these pheromones that they can even be tricked by the right scent.
Red worker ants will care for blue butterfly caterpillars because they smell exactly like ant grubs, even if they look entirely different.
Imagine confusing a baby giraffe for a human baby because they smelled the same!
It’s difficult to compare the sense of smell between animals.
Smells, or odors, are diverse and almost unquantifiable.
We can’t look at a molecule and determine how it will smell, nor can we rely on one molecule smelling the same to multiple people.
In fact, the same odors might smell differently to one person based on which image they’re prompted with.
If shown a picture of Raclette cheese, people often find an accompanying pungent scent to be appetizing.
But if shown a picture of a dirty sock, they find the exact same scent to be disgusting.
Like our sense of smell, our sense of taste relies on molecules that our taste receptors come into contact with, then interpret with a signal to our brains.
We can easily understand the link between these two senses by considering what happens when we get a cold.
Our sense of smell decreases, which causes food to seem to lose its flavor.
How does that work?
Well, when we lose the ability to smell food, the taste of it doesn’t actually change.
In other words, what we taste is exactly the same with or without a stuffy nose.
But when we can’t sense the odorants – the molecules we smell – from the food, the flavor is indeed reduced.
That’s because flavor comes from the combined taste and smell of our food.
Next time you have a cold, you’ll know why your food seems to taste different!
Speaking of food, we humans tend to identify our food first by sight, and then by smell and taste.
A touch of vibration
But star-nosed moles identify their food using touch.
The fleshy protuberances on their noses – eleven points that resemble a star – are extremely sensitive to touch.
The mole presses this star against its tunnel walls and floor at a rate of dozens of presses per second.
This probably helps the mole build a mental map of its surroundings, like how we might use our hands to build such an image in place of sight.
Of course, we can’t know for sure how the mole interprets what it feels with its nose because we don’t speak the same language and can’t read its mind.
But we can tell that the mole uses its nose to distinguish textures at the very least.
Star-nosed moles will eat dead pieces of earthworms.
But they ignore pieces of silicon and rubber, even if they’re similar in size.
In fact, the moles’ stars are so sensitive – and their brains so quick at interpreting the stars’ signals – that they can complete the entire process of identifying and eating a piece of food, then moving on to search for more, in as few as 120 milliseconds.
That’s faster than a human eye can blink.
Star-nosed moles aren’t the only animals relying on incredibly sensitive touch receptors.
Crocodilians – which include crocodiles, alligators, and their other animal relatives – have small bumps all over their chins, snouts, and even within and around their teeth.
These bumps are sense receptors that can sense the smallest ripple from prey as well as the vibrations on the water’s surface from males’ mating calls.
The bumps might also help parents provide just enough force to help their young break free from their eggs, or to sense food and adjust their bites accordingly.
These bumps are even more sensitive than our fingertips, which can detect a quarter of a millimeter difference in the space between ridges!
Another type of touch is a sensitivity to vibrations.
In our world there’s almost constant movement, but humans can’t sense the miniscule vibrations through the ground beneath our feet.
Other animals can.
Tick-trefoil treehoppers, a kind of bug that looks like a leaf, use vibrations to communicate.
They land on actual leaves and vibrate the surface with their feet.
They do this to track down mates, call for help, or just invite others to hang out.
Although we can’t feel or hear these vibrations on our own, if you clipped a microphone to a leaf with communicating treehoppers on it, you’d hear those vibrations translated into something like a strange melody.
It just goes to show that not all senses of sight are used in the same way.
Ants can be tricked into caring for other species’ offspring if they smell right, and other animals use pressing touches and vibrations to identify food or communicate.
But what about some of the even more spectacular senses animals have developed?
We’ll cover those next.
Unusual (and unusually sensitive) senses
Although humans sense infrared radiation to a certain extent – we feel it as heat, like from a fireplace or a hot oven – we definitely don’t have the finely tuned sense of it that melanophila beetles do.
Our ability to sense infrared radiation dies off once we get far enough away from the source – which could be anywhere from a few feet to a few hundred feet if the source is big enough, like a bonfire or forest fire.
But the fire-hunting melanophila beetles have fluid-filled spheres in pits under their wings.
These spheres are so sensitive they detect infrared radiation from forest fires dozens of miles away.
That’s right, dozens of miles.
The beetles then fly to the fire, mate within its flames, and lay their eggs on cooled, charred bark after the fire.
Talk about a fiery romance.
Another force we humans can’t sense, unless it’s overpowering, is a magnetic field.
The earth itself produces a giant magnetic field, thanks to the way its molten, metal core moves.
Humans can use compasses to navigate based on this field, but we can’t sense it ourselves.
As we mentioned earlier, it’s fairly common knowledge that birds rely partially on their magnetoreception, or sense of magnetic fields, to migrate during the winter.
But sea turtles and spiny lobster use it too.
Baby sea turtles use magnetoreception as a guide into the ocean and deeper waters.
They use it again to return to the beaches they hatched from to lay their own eggs as adults.
Ken Lohmann conducted experiments in the 1990s with newly born loggerhead turtles.
When exposed to magnetic fields mimicking various locations in the ocean, they turned and began swimming in the direction that would keep them traveling along the path adult turtles take in the ocean.
The new hatchlings did this without ever having been in the ocean.
They must have been relying on innate instincts and the magnetic field they were sensing.
Spiny lobsters use magnetoreception to return home after hunting day trips.
Even when driven over land, exposed to random magnetic fields, and released in the ocean hundreds of miles from where they’ve lived their entire lives, spiny lobsters will unerringly start off in the exact direction to their distant homes.
Closely related to magnetoreception are electroreception and electrolocation.
Electrolocation is the active sense of creating an electric field to sense the world.
Certain fish, like electric eels and knifefishes, use stacked electrocyte cells to create a flow of ions – charged particles – and thus generate an electric field around their body.
Special electroreceptors then sense disturbances to the generated electric field, which are caused by other animals or objects.
Electric eels can even generate enough electrical charge to kill a horse.
But other fish only generate enough of a charge to deliver the same shock that licking a battery might.
(Just to be clear, we’re not by any means recommending that you do this!
) While some fish generate electric fields and use their electroreceptors to sense changes to those fields, other species use electroreceptors to detect the natural bioelectric fields that living animals create.
These fields are much smaller than those intentionally created by electric eels and knifefishes.
But animals like sharks and rays can sense these fields anyway with their sensitive electroreceptors.
That means sharks and rays can hunt the electric fields created by their prey whenever their sight or smell fails them.
As if having to worry about the smell of blood in the ocean wasn’t enough .
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Final summary
Animals sense the world much differently than we humans do.
Though we can look at modified pictures to understand dichromatic views, we can’t yet build true understandings of what it would feel like to sense the world’s magnetic fields or living creatures’ bioelectric fields.
For these experiences, we can only use our imaginations.
But when we do, we can discover entirely new ways of thinking about our surroundings.
We can develop more empathy for the creatures we share the world with, and understand how the way we live might be affecting their sensescapes – their sensory experience of the environment.
And with these newfound ideas, hopefully, we can work toward living in harmony with the world around us.