Comparative anatomy and physiology play an important role in veterinary medicine. Understanding how differences in structure and function between species influence their daily lives and behaviours is both fascinating and enriching. For your information (and for fun!), here are a few interesting facts comparing key senses in dogs, cats, and humans.
Vision: seeing the world differently
Rods are responsible for night vision and motion detection. In dogs and cats, most photoreceptors (that is, light-sensitive cells that convert light into electrical signals) are rods. This allows them to see much better than us in low-light conditions.
Our pets’ eyes also contain a structure called the tapetum lucidum, which reflects light back toward the rods, amplifying available light. In cats, this structure is more developed than in dogs, making them true champions of night vision.
Colour perception
Colour vision depends on the presence of photoreceptors called cones, located in the retina. In humans, cones make up 100% of the center of the retina, whereas in dogs they represent only about 10%.
Dogs and cats have what is known as dichromatic vision, meaning they perceive only two types of colors: blue and yellow-green. Humans, on the other hand, have trichromatic vision, allowing them to distinguish blue, green, and red.
To illustrate these differences*:
| HUMAN | CAT | |
| Maximum cone concentration (colour vision) | 199,000 | 27,000 |
| Maximum rod concentration (night vision) | 160,000 | 460,000 |
Smell and taste: each species has its own particularities
Humans have about 5 million olfactory receptors, while dogs and cats can have over 200 million. Cats appear to be even more efficient than dogs and humans, when it comes to distinguishing odours.
There are three types of olfactory receptors. The V1R receptor is responsible for the ability to differentiate one odour from another. Humans have two variants, dogs have nine, and cats have no fewer than thirty.
When it comes to taste, cats have only a few hundred taste buds (around 470 on average), dogs have about 1,700, and humans nearly 9,000. Dogs are sensitive to sweet flavors and often prefer new, fatty foods, much like we do. Cats, however, respond mainly to salty, sour, and bitter flavors and have a very limited response to sweetness.
When encouraging a dog or a cat to eat, smell therefore plays a much more important role than taste.
Hearing: detecting the invisible
Humans can hear sounds ranging from 20 Hz to 19,000 Hz. Cats can hear frequencies from 20 Hz up to 100,000 Hz, while dogs hear from 15 Hz to 65,000 Hz.
The ability of dogs and cats to move their ear pinnae allows them to pinpoint the source of sounds much more precisely than humans.
A very different perception of the world
It’s important to remember that dogs and cats do not perceive the world the same way we do. Very faint odors or sounds that are imperceptible to us can be extremely overwhelming for our four-legged companions.
I will always remember a trip to the beach with my husband. Sitting at an outdoor snack bar, we ordered hot dogs and hamburgers. We offered a piece of hamburger to a cat that was begging for food. The cat refused it right away… but happily accepted a piece of the hot dog! We decided to heed the warning and ended up eating only the hot dogs ourselves.
In conclusion
Comparing the senses of dogs, cats, and humans reminds us just how differently our companions experience the world. Their vision, sense of smell, and hearing shape their daily reactions and preferences. Understanding these differences helps us interact with them in a more respectful and appropriate way.
*Source: Ron Ofri, 2014
