>>2824
A documentary (I believe Aftermath: Population Zero) speculated that would be how long it would take for the fast majority of buildings to collapse and be buried. The only exception would be huge, but relatively horizontal constructions, like Hoover Dam.
>we have plenty of evidence of humans dating back thousands of years ago
If you are referring to "ruins" like in Greece, Britain, Japan, etc. keep in mind that those places were still being used and were cared for in one way or another - even if it was not the original culture. Without any form of protection the material will quickly deteriorate. For example: a few years ago there was a hubbub about major Italian cultural icons falling apart due to negligence - after only a few decades.
Of course, it's all speculation, but fun speculation nonetheless.
>>2825
Cuckoo bees, cuckoo bumblebees, cuckoo wasps.
Though not the same, slave-making ants are a doozy as well.