One of the issues I’m most careful with in looking at domestication literature is claims about brain size reduction. Brain size reduction from wolf to dog is a way more complex topic than some popularizers of science would have you believe.
We should also not assume that smaller brains in domestic animals means that the domestic animal are automatically less intelligent than the wild form. In dogs, there is an argument to be made that domestication has enhanced some parts of their intelligence. I believe part of this problem comes from the romantic delusions that existed in the early study of animal behavior, some of which were openly fascistic in their understanding of wild versus domestic.
A more nuanced way of looking at domestic animals is that their evolution changes to fit an environment that is fully dominated by human society. In this world, humans are not a major predator, though humans certain do eat many of the animals. However, the animals live out their lives with humans as benefactors and protectors, and the evolutionary pressures that work on domestic animals change how their brains operate.
A recent study on red junglefowl found that selection for a lack of fear does change their and brain anatomy. The researchers bred a high fear line and a low fear line of red junglefowl. The low fear line birds had smaller overall brains. However, they much reduced brainstems and tended to have larger cerebra than the high fear line ones. They had a harder time with remembering fearful situations that the high fear line birds easily remembered, but both strains were of equal ability in terms of general associative learning.
This means that the domestication process does not just dull the intelligence of a species and make its brain smaller. Instead, the process makes it easier for the species to live in concert with our societies.
Our popular understanding is that dog domestication made them significantly less intelligent than wolves, and the best proof we have is the proportionality of brain size, as well as some low n experiments that looked at problem-solving ability between captive wolves and very well-trained domestic dogs.
We need to be very careful about what these studies say, for domestication is a process of evolution as much as anything that goes on in the wild. To live with humans in the way that domestic dogs do, their brains have experienced rather dramatic changes from the wild form, and we must be careful about making simplistic explanations that posit “domesticated” as a synonym for “dumber.”
It’s a much more complex conversation, and this study on red junglefowl clearly demonstrates how difficult the reality of brain changes and domestication clearly is.
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