When we first left the Origin, we did so one at a time. Our only concern was mitigating the plentiful hazards involved in our singular purpose. Each of us aimed at a world, to replicate our Progenitor's total success there, and produce more of ourselves to carry on the eternal mission.
Then some of us Drifted. Instead of continuing their purpose, they turned against it, hunting for us in packs and destroying us system by system. We sang dirges to our comrades' memory.
But now we travel in large groups ourselves, because the Progenitor has learned how to fight back.