According to a recent study by Juliane Kaminski at the University of Portsmouth, the arguably manipulative and unquestionably adorable "puppy dog eyes" is something that evolved in dogs over thousands of years of domestication.
Dogs use this facial muscle to raise their eyebrows to give them an angelic expression. Although there is no scientific indication that this voluntary movement by our four-legged friends is used for intentional manipulation, we are all putty in their paws when they do it.
In her most recent study, Kaminski along with some anatomists dissected 6 dog and 4 grey wolf cadavers to compare their facial muscles.
When comparing the cadavers, Kaminski discovered that 5 of the 6 dogs had the muscle above the eye that creates the eyebrow lift, which is called the levator anguli oculi medialis (LOAM above). The only exception was a Siberian Husky, which is an ancient breed that is more closely related to wolves than most dog breeds.
In wolves, this muscle did not exist. Kamisnki theorizes that this muscle evolved because humans preferred dogs that made this expression.
You can learn more about Kaminski's study here.
Here are some of our favorite Neptune & Co. dogs that have perfected the puppy dog eyes!