For cats it is the pleading purr and for dogs it is the puppy dog eyes but I’d argue that both are rooted in the same process: selective breeding for an attribute which pleases the human and therefore enhances survival.
There is a difference though. Dogs are far more often selectively breed by breeders whereas there are far more random bred cats compared to cat breeds. Therefore cats have self-selectively bred (Darwinian evolution) to develop this pleading, baby-like purr whereas dog breeders have done it for dogs.
It’s all over the internet at the moment and on television. Dogs have developed a extra set of muscles which can change the appearance of their eyes to give them that puppy dog look. This triggers the nurture (parenting) response from humans. Humans are attracted to this facial expression. Over thousands of years breeders have facilitated this evolution of eye muscles to make their animals more popular with humans and to sell more dogs. You don’t find these puppy dog eye muscles in wolves, the dog’s wild ancestor. It is a selectively bred development to make the dog more attractive.
“…domestication transformed the facial muscle anatomy of dogs specifically for facial communication with humans.”Juliane Kaminski and colleagues in “Evolution of facial muscle anatomy in dogs” on PNAS
“We hypothesize that dogs’ expressive eyebrows are the result of selection based on humans’ preferences.”As above.
There are few anatomical differences between wolves and dogs one of which is the eye muscles. There are two kinds of eye muscles which are noticeable in dogs but not developed in wolves.
The major cat version of the above process is the pleading purr which has a faint hint of the baby cry. It seems that cats have developed this themselves over the thousands of years of domestication. The pleading purr manipulates the human companion/guardian’s nurture response (parenting response). As domestic cats are dependent on us for their survival the pleading purr helps in the survival of the domestic cat. This reinforces the concept that domestic cats are in a constant state of kittenhood in relation to people.
“Any time an animal is in that situation, they are going to be scrutinizing their caregivers for any response to any signal they are sending out. Whatever works, they’re going to do it—whether that’s changing a purr, or doing figure eights between their owner’s feet.”C. A. Tony Buffington, a professor of veterinary medicine at The Ohio State University
What Tony is saying is that cats are observational learners. They have learned how to get what they want and need from their human in the human world in which they live.
Concerning cat breeding, you’ll find that some breeds are designed to have baby features, namely large round eyes and round heads. The Persian comes to mind and the Scottish Fold.
The doll face Persian has a baby face and the name supports that observation (‘doll face’ or ‘doll-faced’). The Scottish Fold has a round head because the ears are flattened to the head. This gives this breed a baby-like appearance. We have seen Taylor Swift nurturing her Scottish Fold like a baby. She definitely relates to her cats as babies and kids.
The concept of ‘elegance’ in cat breeding i.e. long legs and slender body, is also designed to attract buyers. I’d include the Oriental Shorthair and modern Siamese in this category. As for the modern Persian, the breeders went too far. They lost their bearings and ended up with a couple of purebred cats which are too extreme which defeated the point of the exercise.