[learnstats2]

It seems more likely to me that this has a human psychological cause, not a genetic cause.

I suggest that - if humans associate e.g. droopy ears with being more friendly, this creates a positive feedback loop whereby those animals with droopy ears receive more positive interactions, show less fear and are modestly more likely to be selected by Belyaev's research for breeding, all other things being equal. Human bias has become a "selection pressure".

This has no implication within genetics, neither genetics of the foxes nor genetics of the humans: it could simply be (increasingly) customary in society including Belyaev's. So, I strongly doubt any genetic cause.

[travmatt]

IIRC there’s an ongoing breeding program a Russian researcher is conducting with foxes - explicitly breeding the friendliest individuals.

In addition to the ears drooping, others morphological differences manifested - the friendliest animals had distinct coat patterns, curlier tails, and then later generations additionally showed shortened legs, tail, snout, upper jaw, and widened skull.

[arkades]

They're also dealing with a genetic bottleneck. As they repeatedly select for a given trait, they can inadvertently select for traits that are correlated /in their original sample population/, which may not be correlated universally.

That is, with a small enough sample, if it just so happened the nicest cubs had (some traits) in common, you can easily end up exaggerating those traits in later generations.

The Russian study is heavily inbred. They only ever had a maximum of 2000 foxes - now bred for a few dozen generations.

[tzs]

Similar traits show up when other species are domesticated.

It's been theorized that this has to do with the neural crest, which is an embryonic structure that the adrenal medulla develops out of. The adrenal medulla produces hormones involved in stress and fear, and so an animal with a less active adrenal medulla would probably be more amenable to domestication.

Several other things also develop out of the embryonic crest, so it could be that which ties together domestication and those various other traits that seem to go with it across many species.

[mannykannot]

That is an interesting reversal of the causality, though if selection is involved, there would be a genetic change in either case, so sorting out the cause could be difficult.

Do people see droopy ears as more friendly? I guess it indicates that the animal is not particularly alert, and so unlikely to be on the verge of aggression.

[learnstats2]

Perhaps people today think droopy ears are more friendly just because (for example) the first domesticated animals happened by chance to have droopy ears.