Are Humans Driving Wily Urban Red Foxes to Self-Domesticate?
Street smart vulpines show fascinating adaptions for living in human environs.
Posted Jun 05, 2020
A new research essay by Dr. Kevin Parsons and his colleagues titled "Skull morphology diverges between urban and rural populations of red foxes mirroring patterns of domestication and macroevolution" caught my eye, and then I found a popular piece by science writer Virginia Morell called "Urban foxes may be self-domesticating in our midst" that provides an excellent summary of this seminal study that might be a difficult read for non-researchers.1
The title for the second essay attracted my attention because of my long interests in the ways in which wolves became dogs—or, as Psychology Today writer and dog expert Mark Derr puts it, how dogs became dogs—via domestication by humans, and what would happen to dogs as and when humans disappear.2
I also had the pleasure of living with a family of red foxes who bred and raised their children for at least six years near my mountain home. They rested, wandered about, courted, mated, hunted, and played right in front of me and local dogs without a care in the world. They were, of course, wary of local predators such as cougars, bobcats, and black bears, but this clever vulpine family clearly adapted to local conditions and did very well when I knew them.
The above essays are available online for free, so here are a few thoughts about what's happening to urban red foxes as they adapt to living in human environs.
First, what does "domestication" mean? A good working definition of domestication is as follows: "Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another group to secure a more predictable supply of resources from that second group." The group of organisms assuming the control are humans, who practice "artificial selection" to produce traits they desire. Dogs provide the perfect example of a domesticated species. Charles Darwin "was also the first to recognize the difference between conscious selective breeding in which humans directly select for desirable traits, and unconscious selection where traits evolve as a by-product of natural selection or from selection on other traits."
The results of the study comparing urban and rural foxes are very interesting. Dr. Parsons and his colleagues found that urban red foxes when compared to rural red foxes show very interesting adaptations to living in human environs. Urban foxes had wider and shorter muzzles and smaller braincases than their rural relatives, and there were non-significant differences between the shape of skulls from females and males. The researchers write, "While not domesticated, urban foxes show reductions in muzzle size, reduced sexual dimorphism, and a narrowed braincase, and it is plausible that taking up residence in the presence of humans would favour individuals with reduced levels of fear and stress (i.e. urban tameness) as it has in other animals ." (Reference 49 from the original paper refers to K. Uchida et al.)
In "Urban foxes may be self-domesticating in our midst," Virginia Morell writes, "Overall, urban foxes’ skulls seemed to be designed for a stronger bite than were those of rural foxes, which are shaped for speed. Perhaps that’s because in the city, a fox can simply stand at a human trash pile and feed on the food we’ve tossed out, where they may encounter more bones that can only be crushed with stronger jaws, [researcher Kevin] Parsons speculates."
The research project generated a number of emails about the notion of self-domestication, with people wondering what it actually means. I do too from time to time. I immediately thought of an interview I did with renowned Harvard University biological anthropologist Dr. Richard Wrangham about his book called The Goodness Paradox: The Strange Relationship Between Virtue and Violence in Human Evolution. In this interview, Dr. Wrangham noted, “'Wild domesticates' is a term I use to describe species that self-domesticated without humans even being present at all. They are species such as bonobos or island animals in which the selective advantage of being less aggressive can occur for a variety of reasons. In bonobos, the reason why males became less aggressive was probably because the species occupied a habitat in which females were able to form defensive coalitions so predictably that they could always form coalitions to chase and control unruly males." So, "wild domesticates" are adapting to local conditions without the aid of humans via some sort of selective breeding.
It's important to stress that urban foxes are not domesticated, but it's interesting to ponder the ways in which we are indirectly involved in their mating patterns. Over time, it would be expected the differences that have been observed in these foxes when compared with rural foxes would be selected because they're anatomical and behavioral adaptations that allow individuals to adapt to places in which humans reside because of anthropogenic—human-caused—pressures. Dr. Wrangham refers to these animals as "wild domesticates" and I prefer his term to "self-domesticates." However, over time, it's possible that wild domesticates might go on to self-domesticate as they continue to adapt to the presence of humans.
This study of the comparisons of urban and rural foxes is extremely interesting and important, and I look forward to similar research on a wider range of species because humans are taking over just about every square inch of the planet they can and individuals of numerous species will have to adapt or perish. Selection for variations in the strength and speed of biting in red foxes shows just how fine-tuned evolution can be.
There's no reason at all to think that this is a rare case of how nonhumans will have to adapt to the presence of humans when they're forced out of their natural homes. They don't really have a choice if they want to survive in an increasingly human-dominated world.
1) Being "a difficult read" is not meant to be pejorative. The methods used and data analyses necessarily involved some rather sophisticated techniques with which many if not most non-researchers are likely unfamiliar. The abstract for this paper reads, "Human activity is drastically altering the habitat use of natural populations. This has been documented as a driver of phenotypic divergence in a number of wild animal populations. Here, we show that urban and rural populations of red foxes (Vulpes vulpes) from London and surrounding boroughs are divergent in skull traits. These changes are primarily found to be involved with snout length, with urban individuals tending to have shorter and wider muzzles relative to rural individuals, smaller braincases and reduced sexual dimorphism. Changes were widespread and related to muscle attachment sites and thus are likely driven by differing biomechanical demands of feeding or cognition between habitats. Through extensive sampling of the genus Vulpes, we found no support for phylogenetic effects on skull morphology, but patterns of divergence found between urban and rural habitats in V. vulpes quantitatively aligned with macroevolutionary divergence between species. The patterns of skull divergence between urban and rural habitats matched the description of morphological changes that can occur during domestication. Specifically, urban populations of foxes show variation consistent with ‘domestication syndrome’. Therefore, we suggest that occurrences of phenotypic divergence in relation to human activity, while interesting themselves, also have the potential to inform us of the conditions and mechanisms that could initiate domestication. Finally, this also suggests that patterns of domestication may be developmentally biased towards larger patterns of interspecific divergence."
Bekoff, Marc. The Strange Relationship Between Virtue and Violence. (An interview with Richard Wrangham about his new book "The Goodness Paradox.")
_____. Dumping the Dog Domestication Dump Theory Once and For All. (A wide-ranging interview with researchers Christoph Jung and Daniela Pörtl.)
_____. How the Dog Became the Dog.
Uchida, K., Suzuki, K. K., Shimamoto, T., Yanagawa, H., and Koizumi, I. 2019. Decreased vigilance or habituation to humans? Mechanisms on increased boldness in urban animals. Behavioural Ecology 30, 1583-1590, 2019.