Or maybe they also go the bellow replacement level population growth like we do know, and they never recover, they simply die out. The tough conditions that c

Or maybe they also go the bellow replacement level population growth like we do know, and they never recover, they simply die out. The tough conditions that created an intelligent species are simply not there after that species changed its environment "for the better", the species cannot evolve fast enough to catch up with its capabilities and the species dies out. Maybe all intelligent life strives for comfort, but once comfort is achieved, it just kills of the species that created it.