The part of our brain that controls hearing and smell shrunk by ten percent when we started to domesticate dogs! Why?
It was about 100,000 years ago that wolves and humans started to keep company and the domestication of wolves began—leading to domesticated dogs as we know them today. When we started keeping the company of our wolf companions, we had barely transitioned in our own evolution from Homo erectus to Homo sapiens.
This means that wolves and people were on a lot more equal a footing than people and dogs are today. We were just two different species with complementary skills that teamed up together. When humans started to domesticate dogs about 10,000 years ago, our midbrains shrunk by about 10 percent! That is the part of the brain that handles hearing and our sense of smell. In dogs, the forebrain started shrinking at about the same time.
In 'Animals in Translation' Grandin suggests the following: "Wolves, and then dogs, gave early humans a huge survival advantage… By serving as lookouts and guards, and by making it possible for humans to hunt big game in groups, instead of hunting small prey as individuals. Given everything wolves did for early man, dogs were probably a big reason why early man survived and Neanderthals didn't. Neanderthals didn't have dogs."
This could mean that dog brains and human brains started to specialize—humans took over the planning and organizing tasks, and dogs took over the sensory tasks like hearing and smell.