There are three basic questions I had after reading her paper. The first concerns the duration of the critical period of socialization and how it’s determined. The second concerns the relative significance of the duration versus the timing of these periods in wolves and dogs. The final and related question concerns how, exactly, the sensory development of wolves affects their more limited capacity for socialization. Here I’ll address these questions in light of my exchanges with Kathryn Lord. In a separate post I’ll reflect on the findings.
In her paper, Lord says the critical period lasts for four weeks in wolf and dog pups alike. For wolf pups the window is open from two to six weeks of age, and for dogs it is open from four until eight weeks. Recall that this is the period during which pups explore their environment without fear of novelty. More precisely, fear is growing continuously during this period until it reaches a threshold at which the period is said to end. (The window continuously closes until it’s shut.) As Lord puts it,
Fear gradually increases starting at the beginning of the critical period. A week or two into the critical period pups might pause or even run away initially (the more novel the more scary), but then they will approach and explore. The avoidance of novelty occurs when they run away and don’t come back to explore the novelty of their own accord, thus, bringing the critical period to a close.
Previously, many experts thought the window for dogs closed at 16 weeks, while for wolves it closed at three weeks. That would mean their critical periods lasted 12 weeks and one week respectively. On this view, the much greater duration of dogs’ period helped to account for why they are so much more socially flexible (and domesticable) than wolves.
Lord said there remains some debate among experts about how to define the critical period. She is using a “more stringent definition and only including the time period when the animal would actively encounter novelty without intervention (some would call it the most sensitive portion of the critical period).” In both wolf and dog pups, there is a relatively well-defined period during which they encounter novelty without it eliciting a fear response. In the case of dogs, after eight weeks the fear response has grown large enough that, left to themselves, they will avoid novelty. However, human beings can intervene and compel dog pups to become familiar with all kinds of things—including human beings—after the most sensitive period is over, up until about 16 weeks, at which time the fear of novelty reaches a maximum and the window shuts. In short, there is considerable social plasticity in dogs after the “most sensitive period” has passed, with the qualification that it requires the intervention of humans.
As Lord’s study shows, the case with wolves is more complicated. Readers of my earlier post may have noticed that while Lord says their critical period of socialization doesn’t end until six weeks, nevertheless wolves can’t be socialized to humans after three weeks. Contrast this with dogs, who can be socialized to humans after the sensitive part of the critical period is over at eight weeks. What gives?
In her reply, Lord said the old view that the critical period for wolves lasted only a week was based on just this fact, that they can no longer be socialized to humans after three weeks. However, other research has shown that wolves don’t begin avoiding novelty until six weeks. So how can the window remain open, but in such a way that humans can’t get in after three weeks? Lord’s hypothesis is that the reason they can’t be socialized to humans after three weeks is because that’s when they begin to hear. And with this we come to the core of her findings and the hypotheses stemming from it. I’ll let her speak for herself, but keep in mind the crucial finding of her study: when the critical period begins for dogs, all of their senses are developed, whereas when it begins for wolves, they are still blind and deaf.
Dogs have fear gradually increasing while taking in information from all senses and they are constantly cross referencing all of that information, allowing for easy generalization. Wolves develop fear and senses simultaneously so they are always taking in scents, but they have to associate new sounds and sights in the presence of developing fear. This does not stop the exploration process, it just means that they are forming associations as they encounter the new sounds and sights. This slows the process down with everything but what already smells familiar. In a natural situation that is ideal, because their own species (and more specifically family) smells familiar. If you want to make another species familiar to a wolf it is very difficult because you have to first get that underlying scent familiar, and you have to do it very early. In dogs this is not an issue: you can add another species in anywhere between 4 and 8 weeks.
Thus Lord proposes that the truly significant fact is not the relative duration of their critical periods, for one can argue that in most respects it is the same for both. Instead, the crucial fact is that not all of the wolf’s senses are developed by the time their critical period begins. As a result, one might say their critical period has a different, less smooth, texture than that of dogs, which accounts for them being more generally fearful of novelty than dogs are. It also accounts for why they may explore novel things during the critical period without finally becoming accustomed or socialized to them after the period ends. Lord told me she thinks the whole area of how fear develops needs more research.
So there you have it. Or some of it, anyway. If you want more, check out her paper.
Update. Here’s a link to my essay reflecting on wolves and dogs, inspired by Lord’s study.