Ryon and her colleagues concede that it's difficult to make sense of these data, since, after all, "if wolves are differentially sensitive to certain odors, they should be more sensitive to substances of biological relevance such as herbivore feces." But they speculate that the animals' rolling around in motor oil and perfume may reflect a mnemonic strategy, wherein the wolves learn about odors that signal potentially important, deviant changes in their environment. These changes may be evolutionarily relevant (competitive predators) or just really weird (a leather-floral mix) and therefore of uncertain adaptive importance.
More recently, another group of animal behaviorists got back into this dirty business, but traipsed down the taxonomic line to spotted hyenas—a scent-rubbing species that is more distantly related to domestic dogs. For a 2002 article in the Journal of Comparative Psychology, Christine Drea and her colleagues were keen to understand the specific function of the behavior, at least as it occurs in spotted hyenas. The authors hypothesize that rolling around in rot serves not only a memory-related function, but also an important social function for hyenas. Whatever information is contained in the odor would be conveyed from one hyena to another, their theory goes, in the animals' characteristic greeting display—a ritualistic activity that sounds remarkably similar to my own reunions with my partner after some time apart:
During a greet, participants first sniff each other's mouth, head, and back, and then, while displaying erections, stand head to tail and mutually inspect each other's genitals, flanks, and bulging anal pouch. … In nature, a hyena that rolls in an odiferous substance ultimately brings that odor back to the clan. If rolling serves a social function, its consequences are likely to be evident when hyenas reunite.
To determine the social function of scent-rubbing in this species, an investigator surreptitiously squirted one of two different odors (either carrion, which reliably elicits spontaneous rolling among wild hyenas, or camphor, which doesn't) upon the necks, head and shoulder regions of individual hyenas while petting them. Then the "odor-wearer" animal was released into the yard and its behavioral interactions with another hyena, the "odor-perceiver," were observed.
As predicted, hyenas perfumed with carrion received significantly more attention than did the camphor-dappled or those not wearing any odor. Donning eau de carrion led to heightened and positive social interactions—lots of anal bulging—between the two, regardless of the social status of the odor-wearer. Termination of the ceremony also ended peacefully with the carrion odor, unlike some of the other greetings, which met with aggression. It's probably wise to be on friendly terms with the guy who can lead you to the meat. (Or the gal, but female spotted hyenas have faux male genitalia, so gender-equality grammar may be overkill here.) "As olfactory cues and social sniffing are frequently used to unify the clan or to rally hyenas into group activity," Drea and her co-authors conclude, "rolling may ultimately promote social cohesion."
It's not clear how much of these wolf and hyena findings you can extrapolate to your own dog's behavior next time she rolls around in rotting duck gizzards or badger vomit. But cut your bitch some slack and don't make her feel ashamed about it: The putrid smell of microbial fermentation is her own personal Geminesse.
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