How were the foxes compared?
Researchers examined nine preserved silver fox brains, cut into thin slices, from the three groups in the table.[1]
| Fox group | Brains |
|---|---|
| Bred for tameness | 3 |
| Bred for aggression | 3 |
| Wild | 3 |
This table shows the sample, not the number of neurons found.
The tame foxes came from a line bred for friendliness toward human caretakers. Researchers looked for markers of different cell types in the ventromedial hypothalamus, a region near the base of the brain.[1]
What difference did researchers report?
The receptor is estrogen receptor alpha, a protein found in certain neurons. Cornell reports that the tame foxes had fewer neurons expressing it in the hypothalamus.[1]
Earlier mouse research helped the team choose this brain region. In mouse experiments, activating neurons with this receptor in the same region prompted attacks on other mice. That does not establish what the neurons do in foxes.[1]
What remains unknown?
The study does not establish what the cell difference means for fox behavior. With only nine brains, it also cannot show how representative the sample is. The finding is a clue for further research, not an explanation of why an individual fox is tame.[1]