Humans have been selectively breeding dogs for particular tasks for thousands of years. 5,000-year-old drawings from ancient Egypt show at least 2 different types of dogs, one similar to today’s mastiffs and one similar to today’s sighthounds.
The modern interest in breeding dogs for certain looks is much more recent, not really taking off until the Victorian Era.
We tend to think of these two things, breeding for behavior and breeding for looks as separate, but they are linked. Changing a dog’s body type can change its behavior. Let’s look at a couple examples.
Built to Smell
Scent hounds have lots of fascinating, anatomical changes that improve their sense of smell, making exploring the world via smell more interesting to them, which leads them to do it more.
Long ears - Their ears touch the ground when their head is down, helping to stir up scent molecules.
Excessive drool - Extra drool helps them bring scent molecules into their nasal passages and onto their vomeronasal organ, a scent detecting organ in the roof of their mouth.
Longer nasal passages - Hounds have longer nasal passages, which means they have many more scent receptors.
Short legs - Basset hounds’ short legs mean their noses are closer to the ground, making them more likely to notice a smell and making it easier for them to follow a scent trail along the ground.
Different Face Shapes, Different Hobbies
There is massive variety in the shape of dogs’ faces, and it impacts what draws their attention in different situations. Dogs with long noses and eyes farther to the sides, like Labrador Retrievers or sighthounds, have more visual streak, a band across the retina with a high concentration of receptors that give them panoramic vision that is also much better at detecting movement. This makes them more likely to notice and chase critters or tossed balls.
Dogs with short noses and eyes that are positioned closer to the front of their faces have vision that is most similar to ours. They don’t have the same sensitivity to movement or enhanced peripheral vision as other breeds, making them less likely to notice and react to thrown toys or moving critters. But, they do have an improved ability to focus on objects right in front of them, which gives them an advantage over other dogs when it comes to finding treats on the ground.
Sources
Inside of a Dog: What Dogs See, Smell, and Know by Alexandra Horowitz