Second thread on the evolution of like, in the Archaen and Proterozoic eons. There are many kinds of eyes, and many have arisen quite independently; the classic example of convergent evolution. Did sexual reproduction arise more than once, independently? Is it too an example of convergent evolution? If so, what are the details? Specifically, did sexual reproduction arise independently (if at all) in each of, or some proper subset of, the six eukaryote supergroups? I'm not really interested in cases where sexual reproduction was lost, then re-emerged; I'm only interested in independent 'firsts'.