With the sad news of Lyudmila Trut’s passing, we take a moment to reflect on the groundbreaking work she accomplished for both science and the understanding of fox domestication.
Before going further into the topic, I will start by explaining what domestication means.Domestication is the process by which a population is altered through selective breeding for specific traits, accompanied by a reduction in natural selection pressure. Humans are the ones who choose these traits. While natural selection favours traits that enhance survival, such as efficient food acquisition and predator avoidance, domestication prioritises traits that are desirable to humans. During domestication, certain preferred traits are selected, but other correlated traits may also be unintentionally selected. This can result in domestication syndrome: changes in the appearance and behaviour of the species. A great example of domestication is the case of wolves and dogs:
The fox domestication experiment
In an attempt to understand the steps of domestication, a researcher, Dmitri Belyaev, along with Lyudmila Trut, began a pilot study in 1959 in Russia using wild silver foxes. The purpose of this experiment was to mimic the domestication process that wolves underwent to evolve into dogs. The scientists were particularly interested in domestication syndrome, which includes traits such as juvenile features, floppy ears, curly tails, and lower levels of stress hormones.
To conduct the experiment, Belyaev selected a non-domesticated species: the silver fox. He hypothesized that the genes associated with these traits were linked to those associated with tameness. To test this idea, the researchers bred only the calmest and most docile foxes. Lyudmila Trut explained the process:
"When a pup is one month old, an experimenter offers it food from his hand while trying to stroke and handle the pup. The pups are tested twice, once in a cage and once while moving freely with other pups in an enclosure, where they can choose to make contact either with the human experimenter or with another pup."
The pups are tested every month until they reach the age of six or seven months. After that, they are assigned to a class, ranging from the friendliest towards humans to the most aggressive.
By the fourth generation, some pups began interacting with humans by wagging their tails, similar to the behaviour observed in dogs. After six generations of carefully selected foxes, some new behavioural traits began to appear, leading to the creation of an additional category: the "IE" class, for "domesticated elite". The domesticated elite were foxes exhibiting entirely new behaviours. Lyudmila describes them as pups that
"are eager to establish human contact, whimpering to attract attention and sniffing and licking experimenters like dogs."
By the sixth generation, the pups actively sought human interaction and began communicating like dogs, whining, whimpering, and licking humans. Generation after generation, the phenotypical traits of the silver foxes changed. Lyudmila Trut discovered that the domesticated foxes retained juvenile facial and body features, similar to what occurred during the domestication of dogs. However, other traits also appeared among the domesticated foxes: they began to develop floppy ears, depigmented fur, shorter legs, tails and snouts.
After the death of the geneticist Dmitri Belyaev, Lyudmila Trut continued their work and brought it in 1999 to global recognition.
Human gesture reading test
In addition to the behavioural changes observed in the domesticated silver foxes, experiments were conducted to assess their ability to understand human communication gestures. These types of studies have been done for years on wolves and dogs, as dogs are known for their ability to interpret human cues while wolves generally do not pay attention to such cues. Researchers were particularly interested in whether domesticated foxes would display the same behavioural responses as dogs when interacting with humans.
The experiment was as follows: two bowls were presented to the young fox, with some food hidden under one of them. A human experimenter then indicated the bowl with the reward by looking at it and pointing to it with their finger.
The results showed that the domesticated foxes relied more on communicative cues from humans compared to the control foxes (those not bred for tame behaviour).
The same experiment was conducted with young domesticated foxes and age-matched dogs. The results demonstrated that the domesticated foxes were as skilful as the dogs in interpreting human gestures.
Vocalisation towards humans
The domesticated foxes were also tested to determine whether the presence of humans would induce a change in their vocalisations. For this, three groups of foxes were formed: a tamed group, a non-selected group, and a group selected for aggressiveness. An experiment revealed that tamed silver foxes produced unique vocalisations that were not observed in the non-selected foxes or those bred for aggressiveness. All the foxes performed whine, moo and growl. The tamed foxes were the only ones to use cackles and pants, while the other foxes (aggressive and non-selected ones) produced coughs and snorts. Moreover, the domesticated foxes displayed dog-like behaviours when humans appeared, such as tail wagging, rolling onto their backs, or moving on their half-bent paws. All of these observations could indicate that the tamed foxes seek the attention of the human experimenter.
In conclusion, Lyudmila Trut’s groundbreaking work on the domestication of silver foxes has provided invaluable insights into the biological and behavioural mechanisms of domestication. The research demonstrated how selection for sociability can lead to profound transformations, not only in behaviour but also in physiology and communication.
Building on this foundation, the domestication experiment remains ongoing today, continuing to explore all aspects of domestication and expanding to include other species, such as rats and minks.
This approach has inspired other researchers, such as those at Linköping University in Sweden, where researcher Per Jensen is leading a similar domestication experiment with wild chickens (Red Junglefowl) to explore their transformation into modern domesticated chickens. The aim is to determine whether selectively breeding only the calmest Red Junglefowl, generation after generation, will eventually result in the domesticated chicken that we know.
Sources
Trut, L. N. (1999). Early canid domestication: the farm-fox experiment: foxes bred for tamability in a 40-year experiment exhibit remarkable transformations that suggest an interplay between behavioral genetics and development. American Scientist, 87(2), 160-169. https://www.jstor.org/stable/27857815
Hare, B., Plyusnina, I., Ignacio, N., Schepina, O., Stepika, A., Wrangham, R., & Trut, L. (2005). Social cognitive evolution in captive foxes is a correlated by-product of experimental domestication. Current Biology, 15(3), 226-230. https://www.cell.com/fulltext/S0960-9822(05)00092-8
Trut, L., Oskina, I., & Kharlamova, A. (2009). Animal evolution during domestication: the domesticated fox as a model. Bioessays, 31(3), 349-360. https://onlinelibrary.wiley.com/doi/pdf/10.1002/bies.200800070
Gogoleva, S. S., Volodin, I. A., Volodina, E. V., Kharlamova, A. V., & Trut, L. N. (2011). Explosive vocal activity for attracting human attention is related to domestication in silver fox. Behavioural processes, 86(2), 216-221. https://doi.org/10.1016/j.beproc.2010.12.001
Dugatkin, L. A. (2020). The Silver Fox Domestication Experiment: How to Tame a Fox and Build a Dog. Resonance, 25(7), 987-1000. https://doi.org/10.1007/s12045-020-1014-y
Per Jensen page https://liu.se/en/employee/perje15
The cover photo is a photo from Erik Mclean on Pexels:
Great article. It covers some great aspects of Trut's work. She was a remarkable woman and her foxes are fabulous! May she Rest In Peace 🖤🦊