How do cats know to use the litterbox?

Not a question of any consequence, just something I've always been curious about, and I know someone here will know the answer: how is it that, unlike dogs, who have to be housetrained, cats just automatically know to use the litterbox? Is it instinct, or what? I recall hearing that mother cats will teach their kittens to use a litterbox, but I got Meeko at five weeks old, and he'd been raised by people (he was found abandoned with no mother), and he knew to use the litterbox even at that age without me having to teach him a thing, so I'm not sure if it's just that. Anyone have any insight? My apologies if this is a dumb question.

Isn't it amazing? I took in four four-week-olds, and they went right to it!! I think it's just instinct.

Their instinct is to bury their waste, so predators can't track them. But from what I've read and heard, a little instruction by the mom cat comes in handy to show them how to use a litterbox instead of the great outdoors. I've read posts from people with kittens who apparently needed a little help learning to use the box.

Their instinct is to bury their waste, so predators can't track them

That is very true. In the wild (big cats) do this to protect themselves from predators. In addition, males mark (spray) for territory purposes. Amazing how this passes on to our little fuzzy friends over thousands of years.

I've raised 2 orphaned litters and did have to teach them to use the litter box. So simple - just drop some of their poop in there and then stimulate them to urinate over the box. Their instincts take them the rest of the way. The teaching on my part was simply where to go, not how to go.

Yes, it is an instinct to bury.

Here is some bonus information:

When I rescued Nano from the streets, she had a heightened awareness that it was essential to her very survival to adequately cover her tracks. She was not litterbox trained but "knew" to hide her waste in a variety of clever places. She hid her bowel movements in dirty clothes (now dirtier?) that were left on the floor, she urinated down the bathtub drain, etc. So Nano definitely had a strong instinct to not leave anything out in the open.

Even when I finally introduced her to the litterbox, and she understood she could "dig" and "bury" in that area, she was still dissatisfied. Eventually I figured out she was most happy with a very deep layer (6-8 inches!) of litter but she still preferred to escape so she could go outside to defecate. Finally I wised up and bought her two litterboxes, and now she has two separate places for each kind of bathroom business. So that was what it took for Nano to finally become comfortable about going to the bathroom inside.

I have strays, who are now indoor cats only, and they took to the litterbox immediately just like my other kitties who started as kittens. In my opinion, it has to be instinct.