The Timing of Evolutionary Transitions Suggests Intelligent Life Is Rare
How do you differentiate an event that is very improbable and so takes a billion years from an event that is inevitable, but requires many prerequisites, and so takes a billion years?<p>The article seems to simply assume the former model ("We assume that once an evolutionary transition is possible (i.e., once the previous transition has occurred), it occurs at a constant average rate λi, so that each ti is exponentially distributed with an expected transition time of βi = 1/λi"), but that feels unjustified to me.  Is it really the case that the transition from prokaryote to eukaryote was equally likely at any time, and things simply sat stagnant for a billion years until one day life got lucky?