|Photo: MrGarry / Shutterstock|
Theories about the domestication of dogs from wolves suggest that baby-like faces are a by-product of humans selecting for other features. But is it possible they were deliberately selected? A new study in PLoS One by Bridget Waller et al (University of Portsmouth) investigates.
Selecting animals for behavioural traits can end up having unexpected effects on physical characteristics, as shown in the silver fox study by Dimitri K. Belyaev in Siberia. Young foxes were tested to see how they responded to a person, and the least fearful ones were chosen for breeding. Eventually, after forty generations of breeding, the foxes became tame and domesticated. Even though they were selected for behaviour, they had physical changes such as floppy ears, curly tails, blue eyes, different coat colours, less of a ‘foxy’ smell, and a longer socialization period. (You can read more in this blog by Jason Goldman on Scientific American).
This is why the physical appearance of dogs could simply be a by-product of selection for friendly behaviour. Dogs have a wide variety of physical features, many of which are puppy-like – closer to a wolf puppy than an adult wolf. However the scientists wondered if people may have selected for appearance as well as behaviour during domestication.
The study focussed on dogs eyes, since large eyes are seen as a baby-like feature. Using sophisticated facial recognition software, the scientists were able to track a movement known as AU101, in which the inside of the eyebrow is raised, making the eye appear bigger. This is shown in the photograph below of a Rhodesian Ridgeback.
|Source: PLoS One|
A preference for neoteny can even be found in young children, as Borgi and Cirulli (2013) showed in their study using photos of dogs, puppies, cats, kittens, and teddy bears with or without infantile features. Studies of people’s preference for baby-face features typically ask people to make a choice between two photographs. However, Waller et al felt that choosing dogs from re-homing centres is more similar to the domestication process, since it involves selecting a dog that will live in your home.
They enlisted the help of four re-homing centres in the UK, run by Portsmouth City, Wood Green, the Dogs Trust and the RSPCA. Because differences between breeds can be large, they selected 29 dogs from the bull breed group (Staffordshire Bull Terriers, mastiffs, and mixed bull breeds). Each dog was filmed for two minutes while the experimenter stood by the kennel and held out a hand towards the dog. The video was analyzed for facial expression, tail wagging, and time spent near the front of the kennel.
Two dogs were excluded from the results because they had to wait an unusually long time to be adopted (82 and 87 days). The final sample of 27 dogs had an average age of two (ranging from 7 to 96 months).
Surprisingly, the amount of time spent wagging the tail or at the front of the kennel did not make much difference to the length of time that elapsed before dogs were adopted. The eyebrow movement, however, did. If dogs made this eyebrow movement 5 times within the 2 minute period, they were adopted in 50 days (on average), compared to 35 days if they did it ten times, and 28 days for 15 times.
The number of times the eyebrow movement was made when the experimenter was there was considered to be typical of what they would do when potential adopters were first looking at the dog. Testing how many times it was actually made when dogs were adopted would increase the accuracy of the model. And there are also many other factors that could affect adopters’ decisions, including the other dogs present at the centre at the time.
The researchers say the human version of the facial gesture studied here indicates sadness. Even though tail wagging did not have much effect, there was a tendency for dogs that wagged their tails a lot to be at the shelter for longer. So it is possible that sadness, rather than cuteness, influenced people’s choices, although it could also be that sadness is a component of baby-like features. This warrants further research.
This is the first time baby-like features have been shown to affect people’s choice of a dog, something that requires time and investment from the new owner. The researchers say, “Our real world data show that domestic dogs who exhibit paedomorphic characteristics are preferentially and actively selected by humans as pets from rehoming shelters. This therefore supports the hypothesis that paedomorphic characteristics in domestic dogs arose as a result of indirect selection by humans rather than only being a by-product of selection against aggression.” In other words, people may have shown a preference for dogs with infantile features during domestication.
What characteristics first attracted you to your dog?
ReferencesBorgi, M., & Cirulli, F. (2013). Children's preferences for infantile features in dogs and cats Human-Animal Interaction Bulletin, 1 (2), 1-15.
Waller BM, Peirce K, Caeiro CC, Scheider L, Burrows AM, McCune S, & Kaminski J (2013). Paedomorphic facial expressions give dogs a selective advantage. PloS one, 8 (12) PMID: 24386109