This. Mammals are (generally) K-selected species, meaning they invest heavily in raising their young. In the absence of natural pressures, mammals reproduce like crazy until they bump up against the environment's carrying capacity. Humans are not unique at all in our tendency to expand! It's just that we have opposable thumbs and language and tools to help us boost the carrying capacity.

Yeah 'instincts' are in real world just enough external pressure and death to keep the equilibrium going, whatever grisly happens behind the curtains.

Hunters hunt as much as they can. Wolves regularly kill 10 or 20 sheep while eating one if they get the chance. Foxes do similar stuff with chickens. Nature is brutal and without empathy.

Housecats let outdoors often don’t even eat what they hunt, because they have a steady supply of their favorite food in the house. They just hunt and kill because they are furry little murder machines. They really shouldn’t be let outside unsupervised.

> They really shouldn’t be let outside unsupervised.

Alternatively, get them a collar with a little bell, and let them try (and always fail) to hunt.

I guess the odd deaf squirrel wasn’t likely to last long anyway. A bell could work to keep them from stalking. They can still run, leap, and ambush. It seems a bell should at least greatly mitigate the issue. I might say usually rather than always. To be fair, though, supervision won’t stop them every time either.

> They can still run, leap, and ambush.

Whenever they do, there is a little tingle tingle, whatever tiny little movement they're trying to do. They end up unable to catch anything basically, I literally never witnessed one of our cats catching anything growing up, nor them bringing any "gifts".

They don't develop this equilibrium "instinctively" (something exclusively inside them) but they do "naturally" (helped by the environment). Now the reindeer weren't really in their natural environment, they were put in very constrained, special conditions, with little flexibility, little time to adapt, and no ability to shape that environment. The environment forced them to adapt and lower the numbers, and eventually wiped them out with what was also probably a fluke. They were still 50% more individuals than when they arrived but no viable reproduction path ahead.

This was an extreme example. Put humans on this type of island and you'll probably end up with them dying out just the same, despite our tendence to radically change the environment to survive. After all that's why the reindeer were there, so humans can survive absent a constant lifeline from civilization.

Humans, and viruses to a degree, are much better at shaping their environment and adapting faster to what's thrown at them to compensate. The instinct is to change whatever possible of the surroundings to survive and thrive.