Once imitation gets good enough (general and accurate) were capable of spreading behaviors (phenotypes) without having to wait for folks to be born and grow up.
We don't really know what the upper bound for non humans is, because we don't know exactly what's being communicated by, for example, whale song.
It feels like bipedalism, opposable thumbs and strong social behaviour and other factores were the perfect storm at the perfect time.
What seems to be rare is the ability to use culture a medium to store and transmit tech.
What's separates humans is we can construct common fictions that we actually believe in, eg "my job is to maximize shareholder value" where both the corporation and the responsibilities towards it are made up but generally believed.
There's of course a rather large elephant in this room, too, that decides a lot of things about our lives.
Trying to describe culture with stories feels like trying to describe biology with proteins. It gets us most of the way there but also adds a whole ton of complexity because it misses the fundamental nature of the system.
Humans are great at general and accurate imitation. This probably seeded a runaway evolutionary process, the result of which was tools, fire, and language.