An Immense World: How Animal Senses Reveal the Hidden Realms Around Us

by Ed Yong

Sing a note with a frequency of 261 hertz (Hz), and I’ll hear middle C. Such predictability simply doesn’t exist in the realm of smells.

Smell, its vomeronasal variant, and taste are chemical senses, which detect the presence of molecules. They are ancient, universal, and seem to sit apart from the others,

Stretch out your arm and give a thumbs-up. Your nail represents roughly 1 degree of visual space, out of the 360 degrees that surround you.

A human’s visual acuity, then, is somewhere between 60 and 70 cycles per degree, or cpd.

We’ve always looked at butterflies, cleaner shrimps, and zebras through the wrong eyes—ours.

sensitivity and resolution—seesaw against each other. No eye can excel at both.

The left half of a chick’s brain is specialized for focused attention and categorizing objects; the bird can spot food grains among a bed of pebbles if it uses its right eye (directed by its left brain), but not its left eye. The right half of the brain deals with the unexpected;

critical flicker-fusion frequency, or CFF. It’s a measure of how quickly a brain can process visual information.

Each curve represents one class of cone cell; the peak of each curve shows the wavelength of light to which the cone is most sensitive. Note that dogs have two cone classes, while humans have three.

The first primates were almost certainly dichromats. They had two cones, short and long. They saw in blues and yellows, like dogs.

Most primates eat fruits, but at times when those aren’t ripe or available, larger species can make do with young leaves. That’s the “perfect setting for the evolution of trichromacy,” says Amanda Melin,

The trichromats are indeed better at finding brightly colored fruit, but the dichromats surpass them at finding insects disguised as leaves and sticks.

By comparison, a bird’s color vision is a pyramid, with four corners representing each of its four cones. Our entire color space is just one face of that pyramid, whose spacious interior represents colors inaccessible to most of us.

Nociception is the sensory process by which we detect damage.

Nociception is an ancient sense. It is so widespread and consistent across the animal kingdom that the same chemicals, opioids, can quell the nociceptors of humans, chickens, trout, sea slugs, and fruit flies—creatures separated by around 800 million years of evolution.

Why should nociception suck? Some scientists suggest that unpleasant emotions might have intensified and calcified the effect of nociceptive sensations, so that animals not only avoid what is currently hurting them but also learn to avoid it in the future.

Nociception says, “Get away.” Pain says, “…and don’t go back.”

Mint cools because it contains menthol, which activates the cold sensor called TRPM8.

It’s likely that the majority of animal species are parasites, which survive by exploiting the bodies of other creatures.

common repellents like DEET and citronella don’t disrupt a tick’s sense of smell but do stop them from tracking heat.

Meissner corpuscles respond to slow vibrations:

Pacinian corpuscles respond to faster vibrations:

touch is one of our least-studied senses.

Movement transforms touch from a coarse sense into an exquisite one.

animal ears become more adept at discriminating between similar frequencies if their neurons integrate sound information over longer periods of time.

But in doing so, they also become less sensitive to fast changes that occur within those periods.

These spectrograms show the echolocation calls of two bats as they approach an insect. Note that the FM bat’s calls cover a wide range of frequencies, whereas the CF bat mostly holds the same note. But both bats produce shorter and more rapid calls as they approach their prey.

Conductors shine brightly upon it. Insulators cast electric shadows.

Even on calm, sunny days, the air carries a voltage of around 100 volts for every meter off the ground.

Spider silk picks up a negative charge as it leaves a spider’s body, and is repelled by the negatively charged plants on which they sit.

exafference, signals produced by stuff happening in the world.

reafference, signals produced by an animal’s own actions.