It looks like the first eukaryotes picked up thousands of genes from prokaryotes, but then ceased to ply any trade in prokaryotic genes. The simplest explanation for this picture is not bacterial-style lateral gene transfer, but eukaryotic-style endosymbiosis. On the face of it, there could have been scores of endosymbioses, as indeed predicted by the serial endosymbiosis theory. Yet it is barely credible that there could have been 25 different bacteria and 7 or 8 archaea all contributing to an early orgy of endosymbioses, a cellular love-fest; and then nothing for the rest of eukaryotic
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