An evolutionary transition is when the selection process of evolution operated on autonomous organisms at a level where they achieved some kind of sembiotic relationship. The famous example is mitochondria entering the cell of another bacteria, enabling the transition from procureo to cariot cells,. That's the classic historic example. So because evolutionary transitions are very rare, they have no precedent in history. One reason they're very rare is that they're very likely to fail. They might be attempted a lot of times, but they fail most the time. Here we are as humans. We need to figure out how to guide ourselves through an evolutionary transition of astronomical scales for our entire planet. This may be the only planet to