All Cells With Mitochondria Have A Nucleus, All Cells With A Nucleus Have Mitochondria (or Denegerated

All cells with mitochondria have a nucleus, all cells with a nucleus have mitochondria (or denegerated former mitochondria). It's not obvious that this should be so. In general, you should get branching after every trait (ofc this isn't always the case). If organisms with trait A are successful then there should be enough of them to branch. If they require trait B to be successful, trait A shouldn't have reached fixation in the first place, unless they were both caused by the same genetic modification.

Nick lanes theory, in the vital question, is that the mitochondria *directly* caused the development of the nucleus. If you're an archeon with bacteria living inside you, and one of them dies, it's membrane will dissolve and release its genetic material. You're an archeon, so you're used to doing lateral gene transfer, and will copy it's code into yours. This code has a poison and it's antidote

Bacterial genetic code has self-replicating parasitic genes. these genes are adapted to their bacterial host and splice themselves out before transcription. bacteria face strong selection to pare down their genome, so they dont have very many of these. but if you suddenly acquire a huge amount of bacterial genetic code, the parasites therein, not adapted to you, will put themselves in all sorts of bad places. then, because you dont face very strong selection, if these codes mutate in a way that breaks their ability to copy themselves, and splice themselves out before transcription, youll have a bunch of faulty genes. these dead regions are called introns. this is a huge problem! you can develop a protein to splice them out "manually", called the spliceosome, but it works slowly, too slowly to get them all fixed before they reach the ribosome to be made into proteins

HOWEVER, this bacterial code will also have a bunch of genetic code for bacterial membranes. the archeon will start producing a bunch of extra membrane enzymes, which will go around producing extra membranes. without adaptations to handle these, theyll just build up. around where theyre produced. lipids naturally form into closed surfaces in solution, so you'd end up with a bunch of lipid "bags" around your genome. but those bags are the solution to your intron problem! they impede the diffusion of the rna from the genome to the ribosome, giving the spliceosome time to work.

eventually (its theorized) these lipid bags evolved into an enclosed double membrane with pore membranes, but during mitosis they split into discrete lipid bags again!