It's long puzzled biologists why dogs have become man's best friend while wolves remain fiercely wild, when genetically the two are so similar.
Now, new research from the University of Massachusetts Amherst suggests the difference is related to the animals’ earliest sensory experiences and the critical period of socialization.
Evolutionary biologist Kathryn Lord studied how seven wolf pups and 43 dogs reacted to both familiar and new smells, sounds and visual stimuli, and found they developed their senses at the same time.
But she also discovered the importance of a four-week developmental window, called the critical period of socialization. During this period, wolf and dog pups begin walking and exploring without fear.
Domestic dogs can be introduced to humans, horses and even cats at this stage and be comfortable with them forever. But as the period progresses, fear increases and after the window closes, new sights, sounds and smells will elicit a fear response.
Through observations, Lord confirmed that both wolf pups and dogs develop the sense of smell at age two weeks, hearing at four weeks and vision by age six weeks, on average. However, the two subspecies enter the critical period of socialization at different ages.
Dogs begin the period at four weeks, while wolves begin at two weeks, at which point they're still blind and deaf.
"No one knew this about wolves, that when they begin exploring they’re blind and deaf and rely primarily on smell at this stage, so this is very exciting," she says.
"It’s quite startling how different dogs and wolves are from each other at that early age, given how close they are genetically."