We have seen that science has discovered the last eukaryotic common ancestor was essentially as complex as a modern day eukaryotic cell (see here and here and here). Furthermore, I have argued that this complex cell plan that has defined eukarya since the time of LECA has worked to facilitate the eventual emergence of metaozoan-type complexity.
So perhaps it is time to begin contemplating the origin of this complexity.
That is, let’s begin to focus on the transition that occurs on the left half of this figure:
So here is the first question to consider. According to the Modern Synthesis, evolutionary transitions occur as small, gradual, incremental steps. Did the complex state of LECA arise through such gradualism? Was it a slow, gradual transition that reached across a huge span of deep time?