I personally believe there are four great-filters. We're moving through the 3rd, with no solution for the 4th: 1. Water bearing & warm planet. 2. Plenty of ti

I personally believe there are four great-filters. We're moving through the 3rd, with no solution for the 4th: 1. Water bearing & warm planet. 2. Plenty of time for eukaryotic cells to develop. 3. Intelligent life doesn't destroy itself (by whatever means), and is not destroyed by highly unlikely events. 4. Heat death of the universe.