I once ran a Traveller RPG exploration campaign where one of the systems they visited looked really odd on sensors. Just fuzzy clouds and clumps and ring formations of diffuse metallic debris. It turned out it was all paper clips.
This explanation is also the reason why finding basic life (say, bacteria) in the Solar System would be a cause for worry - if life evolved independently twice in the same star system, it would imply abiogenesis isn't that unlikely - thus strongly suggesting the great filter is still ahead of us.
Perhaps it's a combination of factors? Dolphins are social animals that appear to be capable of complex communications among themselves, but don't have hands to manipulate their environment the way we can.
Apes have hands, but don't have complex language.
The surprisingly addictive game is below.
