- Domesticated mammals have smaller brains than their ancestors in the wild. This is true for dogs as well.
- The more genetically distant a dog is from wolves, the larger its brain is, based on samples from 159 breeds.
- The increase in canine brain size has to do with the pressure of dealing with our complex human social life.
According to new research out of Hungary and Sweden, the brain size of modern dog breeds is becoming larger. This is in comparison to more ancient breeds which go back thousands of years and are genetically closer to wolves. Furthermore, the reason for this increased brain size turns out to be somewhat of a surprise.
Dog Brains and Dog Jobs
A team of researchers headed by László Zsolt Garamszegi, an evolutionary biologist at the Centre for Ecological Research in Vácrátót, Hungary, recognized that for scientists interested in brain structure and evolution, dogs are potentially a wonderful source of information. The domestication of dogs probably occurred between 14,000 and 20,000 years ago. For the first few thousand years dogs looked pretty much like their wolf ancestors with nothing like clearly defined dog breeds.
However, nowadays we have over 400 recognized breeds of dogs, many of which evolved over the past 200 years as humans began to breed dogs for different tasks. These new canine jobs vary in terms of complexity, with some dogs specifically bred for hunting, tracking, herding, or guarding, and even many dog breeds that have been purposefully designed to be companions. Some of these canine functions appear to be much more complex than others. Thus it makes sense to ask the question as to whether there is a correlation between brain size and the specific tasks that a breed was created for. Put simply, the issue becomes something like "If we control for body size, does a herding breed have a brain size that differs proportionally from a lap dog?"
Answering this question requires a lot of dog brains, or at least skulls, plus an incredible number of precise measurements and lots of computing power. Fortunately, Tibor Csörg at the Department of Anatomy, Cell and Developmental Biology at Eötvös Loránd University in Budapest has been collecting canine skulls for decades. CT scans of the skulls were performed, and based on the images and some powerful computer programming, it was possible to reconstruct the brains and determine their exact volume.
This collection of skulls was augmented by the Canine Brain and Tissue Bank at the same university. It has been in operation for around seven years and provided a set of actual dog brains. Taken together, the research team ended up with a databank from 865 individual canines, spread across 159 dog breeds, with an additional 48 specimens representing wolves.
The Domestication Effect
Before we go much further it is important to point out that the very process of domestication has an impact on brain size. The "domestication effect" refers to the fact that the brains of domesticated animals are almost always noticeably smaller than the brains of their undomesticated ancestors. It is assumed that this effect occurs because the lives of domesticated animals are simpler in comparison with those who still live in the wild. Think of it this way, the domestic animal lives in an environment provided by humans where there is no need to worry about predator attacks or to spend much energy hunting for food.
The mammalian brain is a metabolically expensive organ. In dogs, the brain uses about 10 percent of the total metabolic energy even though it only accounts for 2 percent of total body mass. (Human brains are even more expensive, using about 20 percent of our metabolic energy.) Large brains would not have evolved if they did not give animals a significant advantage. A domesticated animal simply does not need that costly big brain when that same energy can be directed toward other purposes, such as producing more offspring.
One of the results of this recent study was that it confirmed the expected domestication effect for dogs. The data showed that absolute brain volume of wolves is 24 percent larger than that of domestic dogs. However, contrary to the investigator's predictions, despite the fact that the various breeds are created for such a multiplicity of different purposes that differ in complexity, there were no associations between brain size and functional breed categories.
The researchers did find one unexpected result. What surprised researchers is that the greater the genetic distance between a dog breed and wolves, the larger its relative brain size has become. They conclude: "This suggests that, after the initial decrease in brain size upon domestication, subsequent intentional selection of specific traits through selective breeding favored brain size increases. Therefore, some selection for increased brain size has been continuously occurring in dogs."
The Social Brain
What is causing this expansion in the size of dogs' brains? The answer may well lie in what is often called the "Social Brain Hypothesis". This idea was first proposed by Robin Dunbar, Emeritus Professor of Evolutionary Psychology at the University of Oxford.
The idea behind the social brain hypothesis is that a more complex social environment requires an increased level of social cognitive abilities which need the support of a larger brain size. This is because when an individual is living in a social group he must consider the implications of each of his behavioral interactions in terms of how it affects the behavior of others in the group. For example, for each social interaction, an individual might go through the thought pattern "If I do this, then he will do that, which might require that I respond in this way and…" Similar social problem-solving must be done many times a day in a social group.
Dunbar's first studies involved looking at the brains of primates. In these studies, he confirmed that the larger the typical living group size is for a primate species, the larger the average brain volume is. He then went on to confirm these results in a variety of other mammalian species. Dunbar concludes that "the balance of evidence now clearly favors the suggestion that it was the computational demands of living in large, complex societies that selected for large brains."
Early domesticated dogs were not as tightly integrated into the social lives of people as are today's dogs. Contemporary society is more complex and we have incorporated our dogs into our families. We interact with our pet dogs socially, almost as if they were human children. A typical dog will have dozens, if not hundreds, of social interactions with members of its family, or other human beings that it meets during walks and other activities, almost every day. As we have seen, each social interaction is really a sort of cognitive problem. With so many cognitive problems to solve on a regular basis, it requires, and justifies the biological expense of, a larger brain for our modern dogs. It is likely that living in our modern complex social environment is the driving force behind the evolutionary trend towards the development of larger brains in more recent breeds of dogs.
Copyright SC Psychological Enterprises Ltd. May not be reprinted or reposted without permission
Garamszegi LZ, Kubinyi E, Czeibert K, Nagy G, Csörgő T, Kolm N. (2023). Evolution of relative brain size in dogs—no effects of selection for breed function, litter size, or longevity. Evolution, qpad063, https://doi.org/10.1093/evolut/qpad063
Dunbar, RIM. (1998). The social brain hypothesis. Evolutionary Anthropology: Issues, News, and Reviews, 6(5), 178–190. https://doi.org/10.1002/(sici)1520-6505(1998)6:5<178::aid-evan5>3.0.co;2-8