The short period of time is relative – it works faster with domesticated animals. It isn’t just “evolutionary pressure” – that is random, and takes a long time. Breeding of domesticated animals is non-random; it’s clearly directed by humans specifically to produce desired traits, so it works much faster than random evolution.
Also, domesticated animals live shorter than wild ones, so generations turn over faster, thus inherited changes come faster.
These type of questions illustrate the problems of trying to apply human concepts, in this case itelligence to animals.
In this case we have a few natural examples, in that of flightless birds. We’ve all heard of the expression, dumb as a dodo. Well the dodo was quite good, at being a dodo. And it did well, till its environment changed. Then it couldn’t cope so well.
The dodo had everything it needed to survive in its habitat, but it didn’t have the ability to adapt. Other flightless birds show this as well. The moa was wiped out in about a hundred years after humans came to New Zealand. The largest moas had only one preditor, another bird. And that eagle would swoop down from the air to kill them.
And most moas had defenses against being swooped on from above, but they never had the need to think about other defenses. So when humans came they didn’t have the evolutionary time span to get other defenses and were killed off. Shortly afterwards the eagle that preyed on the moa also died out.
California condors are another example. They first released them back into the wild and the condors died because they weren’t afraid of nothing. They then taught the condors to be afraid of power lines and golden eagles (the two main problems) and that solved a lot of the problems with releasing them back into the wild
Domesticated animals have a lot of the cunning either bred out of them or never learn it in the first place. This isn’t really a matter of genes so much as a matter of having a mother cat teach the kittens things like climbing UP AND DOWN a tree.
How many threads do you have about pet owners worried 'cause if they let their cat outdoors it’d climb a tree? Well that’s what cats DO, they climb things. Cats love to balance on things. But domesticated cats often don’t have enough practice to do it right.
So sheep tend to be stupid, even by sheep standards, 'cause they are only bred to be wool and food.
Some breeds certainly seem more intelligent than others- some of the pet breeds and breeds that are left to forage in large unfenced areas (we had a big flock of herdswick sheep locally) act a lot more alert and less prone to doing dumb things like getting stuck on fences than other breeds.
None of them are exactly going to win any Nobel science prizes though…
I haven’t had a large facility, but at various times I’ve had horses, goats, cows, and sheep, and I would rank their intelligence in that order. The sheep weren’t an order of magnitude more stupid than cows, but they were more likely to get lost or get stuck somewhere.
I would not correlate aggression or fear with intelligence. While I would never turn my back on a ram, I wouldn’t say he was any smarter than the wethers or ewes.
On that basis, due to having had no exposure to ballistics and test launches going pear-shaped, I’m apparently more intelligent than the average rocket scientist.
Apparently, sheep are very good at recognizing and remembering faces (nature, National Geographic). This indicates considerable ovine social intelligence.