She hypothesized that an ancient amoeboid creature, an early eukaryote, had acquired the wiggly thing by eating it. Or perhaps the wiggly thing had attached itself to the outside of the eukaryotic cell. Instead of being digested (if it was inside) or causing harm as an internal parasite, or being sloughed off (if it was externally attached), in at least one fateful case, it had become domesticated. It stuck, it stayed, it assimilated. Some of its genes, including those that coded for a particular structural feature Margulis noticed, were incorporated somehow into the coding genome of the host.
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