Dogs and wolves are genetically so similar, it’s been difficult for biologists to understand why wolves remain fiercely wild, while dogs can gladly become "man’s best friend." Biologists think the different behaviors are related to the animals’ earliest sensory experiences and the critical period of socialization.
Until now, little was known about sensory development in wolf pups, and assumptions were usually extrapolated from what is known for dogs. This would seem to be reasonable, except scientists already know there are significant differences in early development between wolf and dog pups.
When the socialization window is open, wolf and dog pups begin walking and exploring without fear and will retain familiarity throughout their lives with those things they contact. 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.
Dogs begin this period at four weeks, while wolves begin earlier, at two weeks when wolf pups are still blind and deaf. They rely primarily on smell at this stage. How each subspecies experiences the world during that all-important month is extremely different, and likely leads to different developmental paths.
Evolutionary biologist Kathryn Lord says, “the difference may not be in the gene itself, but in when the gene is turned on. If you want to socialize a dog with a human or a horse, all you need is 90 minutes to introduce them between the ages of four and eight weeks. After that, a dog will not be afraid of humans or whatever else you introduced.
"Of course, to build a real relationship takes more time. But with a wolf pup, achieving even close to the same fear reduction requires 24-hour contact starting before age three weeks, and even then you won’t get the same attachment or lack of fear."