A world without dogs sounds like no fun at all. But many of the hundreds of dog breed we know today are only a few centuries old, and according to current research if you go back in time at most thirty-four thousand years dogs as we know them didn't even exist. Even though we know that modern dogs and modern wolves share a wolf ancestor no one's exactly sure how dogs were first domesticated, or even when. 

But we do know that at some point dogs evolved from mostly ignoring humans to wanting to be best friends with us. That process of domestication came with consequences. Some of them you'd expect, like dogs becoming tamer over time, and others are just strange.

For instance, there's a trait that dogs share with other domesticated animals that even Darwin thought was weird. Lots of dog breeds have floppy ears. Evolutionarily, this doesn't make much sense. It's a result of deformed ear cartilage that can actually make it harder for a dog to hear. 

So, why would we breed dogs to have deformed ears? Well we didn't at first, at least not on purpose... Instead floppy ears seem to have a lot to do with other traits that domesticated animals have, like patches of white fur and adorable little faces that retain their juvenile features into adulthood. 

According to a new hypothesis it turns out that in the process of domesticating dogs we might have been effecting some of their stem cell. In a dog embryo there's a group of stem cells called the "neural crest" and these cells are responsible for performing a specific set of physical features - like the dog's coat, the structure of its face and its adrenal glands - and according to this new research, a lot of the features that we associate with tameness may actually come from changes that have been made to this neural crest.  

The earliest dogs may have been less aggressive because they had smaller adrenal glands. So when early humans bred for tameness, the dogs probably also ended up with changes to other traits that are controlled by the neural crest - like floppy ears and the faces with more juvenile features, such as smaller jaws. So basically, by domesticating dogs we may have ended up selecting for mutations in their stem cells that made them less like wolves, and more like the animal that is probably sleeping in your living room right now. 

But domesticating dogs has had other useful side effects too. For example, dogs are a whole lot better than their cousins at digesting starch. A study published in 2013 analyzed the genomes of 12 wolves and 60 dogs of different breeds. The researchers were looking for genetic differences that showed up in all of the dogs, but none of the wolves. They found changes in 36 regions of all of the dogs DNA. Some of the results were somewhat predictable, like changes to genes that were involved in brain development which account for how friendly and tame dogs can be. 

But they also found something they didn't expect: the dogs had three genetic variations that helped them digest starch. And this fits with the theory that dogs first started to be domesticated when humans settled down to agrarian life. At some point hungry wolves might have started venturing into human settlements and eating their leftover starchy food (something that a lot of modern dogs seem to be into as well). The wolves that were best able to digest the starch were better fed so they survived to reproduce. 

And speaking of things that dogs are really into - you know how dogs really like chewing on bones but it seems to take them forever to actually finish eating one? Well, that has a lot to do with their ancestry too. Wolves eat meat, and they're really into the stuff. It doesn't matter how delicious you think your pie is, a wolf is going to pick the steak any day. So they've got really sharp teeth that are perfect for tearing flesh apart and powerful jaws that polish off the bone pretty quickly, especially if they're looking to get to the marrow inside.

But even though dogs inherited the wolves desire to gnaw on bones, they have smaller jaws and a less powerful bite, which means that it takes them a whole lot longer to finish a bone (if they can even make a dent in it at all). But if you've ever seen a dog chewing on a bone, it doesn't seem like they mind how long it takes to finish. 

Thanks for watching this episode of SciShow. If you want to keep getting smarter with us, just go to youtube.com/scishow and subscribe.