Dogs are a distinct subspecies of grey wolf that is very different in both appearance and behavior from its wolf cousins. The primary difference is domestication.
Domestication is a genetic event that occurs when a group of animals is kept genetically isolated from others of its kind, and are selected (either deliberately or naturally) for reduced aggression, lower excitability and nervousness, lower fear and vigilance, and affection for humans. The genes that come into play when domestication takes place also make the animals more susceptible to various other mutations including changes in ear length and floppiness, tail length, body shape and size, and coat color.
It’s believed that dogs became domesticated through natural selection as they lived in human camps. (Dogs which had more domesticated traits and temperaments were allowed closer, and got more food). The natural way this happened is the reason why dogs also instinctively look to humans for help when they have a problem that they can’t readily solve (this provided a survival advantage – we didn’t deliberately breed the trait into them). Wolves do not (no matter if they’ve been raised by humans or not). Dogs also pay attention to, read, and readily understand human body language – again, this is a trait they’re born with, and wolves don’t have it.
Dogs do form packs, but they don’t coordinate if they hunt in a pack. Wolves do. Dogs readily accept unrelated dogs into their packs, if they’re properly socialized. Wolves do not. In a wolf pack, only the lead pair (the parents) mate and produce offspring, and all of the wolves (their older offspring, and the occasional sibling who joined them from their former family) help care for them. Wolves dig dens to house their young. Dogs do none of those things – in a dog pack, all females will mate and bear offspring, and only the female cares for her own pups; nor do they dig dens.
Dogs have the ability to produce an enzyme that allows them to get nutrients from starchy plants, wolves lack this enzyme. This is why wolves and wolf-dog hybrids usually cannot be fed conventional kibbles that have a lot of grains, while many dogs do just fine on them.
Some dogs have rear dewclaws while no wild wolves have rear dewclaws. These extra digits are sometimes used to determine if an animal is a protected wolf or a feral dog or dog-wolf hybrid.
Both dogs and wolves bark – but wolves tend to stop barking when they reach maturity. Dogs bark because they never really grow up.
Unlike wolves, male dogs do not typically help to raise their offspring if the dogs are stray or feral. The exception is the Dingo where nuclear-family pack structure resembles that of wolves.
Wolves come into heat (estrus) once per year in the late winter/spring while almost all dog breeds come into heat twice a year and dogs may come into heat during any season.
Surprisingly, Many health conditions in purebred dogs are also found in wolves. These include hip dysplasia and progressive retinal atrophy. This suggests that such conditions are not due to selective breeding, but existed as mutations in the population even before domestication began.
Scientists debate hotly about whether humans instigated domestication of wolves, wolves instigated their own domestication, or if dogs are not domestic wolves at all but a split-off of a common ancestor. Regardless, dogs show a natural willingness to look to humans for direction and a lack of aggression toward us.