There is a fascinating study published recently in the Proceedings of the National Academy of Sciences, and we are grateful to The Atlantic for reporting so well on it, because the topic is so weighty: How and why do humans respond to puppy eyes?

Dogs’ eyes have changed since humans befriended them – or they befriended humans – as long as 30,000 years ago, The Atlantic observes. At that point of contact, when the first one walked into a human camp and was allowed to stay, because it was useful, they were wolves. And over thousands of years, those canids and humans co-evolved.

One hypothesis holds that their watchfulness allowed us to sleep at night, keeping them alert to real danger or, later, a letter carrier, and allowing us to develop our big brains, which we could use to build the internet and order treats for them from Chewy.com.

The study, reports The Atlantic, found dogs’ faces “are structured for complex expression in a way that wolves’ aren’t, thanks to a special pair of muscles framing their eyes. These muscles are responsible for that ‘adopt me’ look that dogs can pull by raising their inner eyebrows. It’s the first biological evidence scientists have found that domesticated dogs might have evolved a specialized ability used expressly to communicate better with humans.”

Our dogs’ ancestors figured out that we like big eyes. We like babies. And they gave us what we wanted, over slow time. And then, other researchers say, when people stare into the eyes of a dog whom they know, they release oxytocin, the hormone that helps mothers bond with children and makes us feel like smiling and sighing.

Dogs have engineered our brains, and all without even mastering algebra. They used patience. Amazingly, some animals can do it quickly, too.

Dmitry Belyayev was a geneticist in the 1950s in the Soviet Union, which was unfortunate for him since Trofim Lysenko, the head of the Soviet Institute of Genetics, was unalterably opposed to genetics. (To understand the old Soviet Union, it still helps to think of “Alice’s Adventures in Wonderland.”)

Belyayev persisted. He worked with silver foxes, a red fox variant, in Siberia, away from prying eyes. You could say he was in internal exile.

The foxes are fierce animals that sensibly resist being killed for their fur. Belyayev made a more docile silver fox. He did it simply by breeding the least aggressive ones.

Darwin observed that domesticated animals became smaller than their wild cousins, with floppier ears and curlier tails. This made them more appealingly child-like to humans, but it was thought to be a change which occurred over thousands of years. Belyayev began to see these changes in foxes in just 10 generations – a blink of the eye in evolutionary time.

It may be that Belyayev’s foxes make just as good pets as some dogs we know, but what is different is our long history with dogs, as work mates and, so often of late, simply as companions, even as therapy dogs.

It is not only because dog anatomy has evolved to where dogs can make puppy eyes at us and get what they want (Out? A treat? A pat?). It is also because we have evolved to cherish them for what they are, even when we do not need them to bring sheep in.

For some dog companions, the best part of the relationship is knowing a dog as an individual and as a representative of a species. It is living in close proximity with a tame being who keeps a little of the wild and also has our on/off switch.

Consciously or not, we have gotten the dogs we wanted. And they, apparently, got the people they want.