The sole ancestor of the dog is the wolf. But how, exactly, did Canis lupus familiaris, the domestic dog we know and love, come to distinguish itself from Canis lupus lupus, the wild wolf?
The story of how dogs evolved from wolves is tolerably clear in outline, but there is still much to learn. Those who love dogs will naturally be interested in their genealogy, since you can learn a lot about an animal’s nature (including our own nature, by the way) by examining its origins. I take up the question of the dog’s evolutionary history in the first chapter of my book about friendship and dogs, on the simple assumption that if you want to be a good friend, it’s very helpful to know who your friend is. And what better place to start than by learning whence their kind comes? Similarly, learning about your own primate history can be very revealing (Robert Wright’s The Moral Animal is one good place to start), just as getting to know the in-laws can help you better understand your spouse.
One obvious behavioral difference between wolves and dogs is that wolves are wild and fearful of humans, while dogs are domestic and friendly. Yet dogs and wolves are genetically very similar; indeed they are regarded as belonging to the same species because they can interbreed and produce fertile offspring. So, what’s responsible for this very different behavior?
One place to look for an explanation is in the timing and duration of their respective critical periods of socialization. Briefly, this is a period very early in their lives when dog and wolf pups explore their world without fear; the things they come across during this time remain a familiar part of their world throughout their lives. As the window of this critical period closes, novel things are likelier to elicit a fear response.
This is why if you want your pup to make a deep psychic adjustment to the bustle and noise of urban life, it’s best to introduce her to it as soon as she’s old enough to walk around. Similarly, if you want your pup to protect your sheep rather than prey on them, it’s a good idea to do as shepherds do, and have the pup spend time in the company of sheep, so that they will regard the sheep as a familiar part of their social world. This period is so critical that a dog pup that’s not been introduced to human company while this window of social opportunity is open will never socialize well with people.
With that as our context, a recently published study by Kathryn Lord (see the journal Ethology for the full paper: “A Comparison of the Sensory Development of Wolves (Canis lupus lupus) and Dogs (Canis lupus familiaris)”) deepens our understanding. Lord’s research confirms that dog and wolf pups develop their senory powers at the same time: the sense of smell at two weeks, hearing at four weeks, and vision by age six weeks on average. However, Lord found that wolf pups are still blind and deaf when they begin to walk and explore their environment at age two weeks. “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 notes. The press release continues,
Meanwhile, dog pups only begin to explore and walk after all three senses, smell, hearing and sight, are functioning. Overall, “It’s quite startling how different dogs and wolves are from each other at that early age, given how close they are genetically. A litter of dog puppies at two weeks are just basically little puddles, unable to get up or walk around. But wolf pups are exploring actively, walking strongly with good coordination and starting to be able to climb up little steps and hills.”
Because wolf pups begin exploring their world while still deaf and blind, Lord speculates in her paper that later “when further exploration occurs (auditory, and visual), it could be limited by the need for a familiar scent.” Since dogs begin exploring later, when more of their senses are developed, Lord suggests that how each subspecies experiences the world early on “is extremely different, and likely leads to different developmental paths.”
The data help to explain why, 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.”
I learned from Lord’s paper that the critical period of socialization is longer in wolves, and shorter in dogs, than has previously been thought. In both cases, she says the window is open for about 4 weeks, from 2 to 6 weeks of age for wolf pups, and from 4 to 8 weeks of age for dogs. Well, it’s not quite that simple. For her paper also observes that while “maximum generalization” ends at 8 weeks, dog pups continue to be open to socialization to as late as 16 weeks, for not until then does their fear of novelty reach its zenith and the window of social opportunity fully close.
It thus appears that dogs’ window closes slowly, whereas the wolves’ bangs shut quickly. This raises an interesting question about the relative significance of timing versus duration of the critical period: is the timing of the critical periods with respect to sensory development more important for understanding why dogs differ from wolves? Or, is the varying duration of their critical periods at least as important a factor? In my book I suggest, following the Coppingers, that the longer period during which dogs can freely familiarize themselves with their local world gives them considerably more behavioral flexibility than wolves have, and this contributes most vitally to their incredible talent for fitting ever so comfortably into a thousand different human settings. It may be, however, that this view will have to be revised once we learn more about how the timing of the windows affects their “different development paths.”
I’ve written to Lord with some questions, so stay tuned for an update and—who knows—maybe some idle speculations on the questions and hypotheses suggested by her very interesting study.