I read Nick Lane’s The Vital Question and he argues that mitochondria came first and sex second. IIRC, he said that small-genome organisms (bacteria & archaea) do sporadic one-off gene exchange with their neighbors, and that process basically accomplishes the same thing that meiosis accomplishes in eukaryotes, i.e. enabling natural selection to act independently on every gene simultaneously. But sporadic one-off gene exchange is not a mechanism that can scale up to really massive numbers of genes. (I forget why not.) Hence, as genome size started expanding in early eukaryotes, they had to switch to meiosis (with crossing-over) at some point.
I have a vague recollection that he viewed meiosis as easy to evolve, with the justification that meiosis-related machinery can be found in some archaea (or something?). But very low confidence that I’m remembering correctly.
By contrast he definitely goes on and on about how you fundamentally can’t have a large genome without mitochondria [part of his argument is in the OP], and how the process of getting mitochondria (via an archaeon endocytosis-ing a bacterium) was an extremely difficult step evolutionarily.
I read Nick Lane’s The Vital Question and he argues that mitochondria came first and sex second. IIRC, he said that small-genome organisms (bacteria & archaea) do sporadic one-off gene exchange with their neighbors, and that process basically accomplishes the same thing that meiosis accomplishes in eukaryotes, i.e. enabling natural selection to act independently on every gene simultaneously. But sporadic one-off gene exchange is not a mechanism that can scale up to really massive numbers of genes. (I forget why not.) Hence, as genome size started expanding in early eukaryotes, they had to switch to meiosis (with crossing-over) at some point.
I have a vague recollection that he viewed meiosis as easy to evolve, with the justification that meiosis-related machinery can be found in some archaea (or something?). But very low confidence that I’m remembering correctly.
By contrast he definitely goes on and on about how you fundamentally can’t have a large genome without mitochondria [part of his argument is in the OP], and how the process of getting mitochondria (via an archaeon endocytosis-ing a bacterium) was an extremely difficult step evolutionarily.