London - When dogs look up at you with those big, cute eyes, it’s hard to resist giving them a stroke or treat.
And that’s no accident as the canines have evolved to look more appealing with sad "puppy dog eyes".
Scientific research has revealed that they have developed muscles allowing them to raise an eyebrow and make their eyes seem larger and more child-like. The effect is to give them facial expressions similar to our own, triggering a nurturing response in humans.
Experts said the evolutionary step took place around 33 000 years when our ancestors began to domesticate wolves.
This is considered a rapid change in evolutionary terms and is the only example of an animal whose facial expression has changed through domestication.