A Brain Shrinking Domestication Event

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In summary, domesticated cattle have undergone significant changes in brain size over the past 10,000 years, with a 25% decrease on average. This is due to selective breeding for docility and may have happened rapidly, as seen in other domesticated animals.
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BillTre

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Domesticated cattle (cows or steers) evolved, under domestication, into a variety of different lines (or strains), from aurochs (Bos primigenius,, now extinct) about 10,000 years ago.
Science mag news article here.
Ana Balcarcel of the University of Zurich and colleagues scanned the skulls of museum specimens, corrected for body size, and determined their relative sizes.
Domesticated strains had about 25% less brain volume on average.
She sorted the extinct and living breeds into five categories based on their primary purpose as livestock: wild, bullfighting, park (referring to cattle that live essentially as pets on rangeland), beef, and dairy. Next, she plotted the breeds’ brain sizes and looked for patterns.She found that bullfighting breeds, which are bred for aggression and tend to have little human interaction outside fighting in the ring, have brain sizes nearly as large as those of wild aurochs. Park cattle, which have relatively little human contact, also have relatively large brains. But beef cattle have far smaller brains, and dairy cattle—which frequently interact with farmers and are bred for their milk yield and gentleness—have the smallest brains of all.
It is thought that the animals were selected for docility in order for humans to be able to work with them.
Balcarcel suspects that when breeders select for more docile animals in beef and dairy breeds, they are selecting for genes that shrink the parts of the brain that control fear, anxiety, and aggression.
The closer interaction with humans, the greater the difference for the wild aurochs.

Other vertebrate animals (pigs, dogs, sheep, cats) have similar patterns.
Some of the cattle strains have only been around for ~200 years, so the changes may have happened rapidly.
However, that kind of conclusion would depend upon what those newer strains started from, already selected to be smaller or not.
 
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It's amazing to see how domesticated cattle have evolved over the course of 10,000 years! By selectively breeding for docility, it seems that humans have been able to shrink certain parts of the brain, resulting in smaller brain sizes in beef and dairy cattle. It's fascinating that this pattern is also found in other vertebrate animals, such as pigs, dogs, sheep, and cats. It's also interesting to note that some of the cattle strains have only been around for 200 years, yet they already show signs of rapid evolution. It would be interesting to know what these newer strains started from, as that would give us a better understanding of whether they were already selected to be smaller or not.
 

1. What is a Brain Shrinking Domestication Event?

A Brain Shrinking Domestication Event refers to the theory that the brains of domesticated animals have shrunk in size compared to their wild counterparts due to the process of domestication. This phenomenon has been observed in various domesticated species such as dogs, cats, and pigs.

2. How does domestication lead to brain shrinkage?

Domestication involves the selective breeding of animals for specific traits, such as tameness and docility. This process can also inadvertently lead to changes in brain size and structure. For example, domesticated animals may not need to use their brains as much for survival as their wild counterparts, leading to a decrease in brain size over generations.

3. Is brain shrinkage a negative consequence of domestication?

There is still ongoing debate among scientists about whether brain shrinkage in domesticated animals is a negative consequence or not. Some argue that it may be a trade-off for other desirable traits, such as increased tameness and reduced aggression. Others believe that it may have negative impacts on cognitive abilities and overall welfare of the animals.

4. Are all domesticated animals affected by brain shrinkage?

While brain shrinkage has been observed in various domesticated species, not all domesticated animals show this phenomenon. For example, domesticated horses and rabbits have similar brain sizes to their wild counterparts. This suggests that domestication may not always lead to brain shrinkage and that other factors may play a role.

5. Can brain shrinkage be reversed in domesticated animals?

There is currently no evidence to suggest that brain shrinkage in domesticated animals can be reversed. However, further research is needed to fully understand the mechanisms behind brain shrinkage and whether it can be prevented or reversed. Some studies have shown that environmental enrichment and cognitive stimulation can lead to changes in brain structure, so it is possible that these interventions may have some impact on brain shrinkage in domesticated animals.

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