Also it appears to have evolved from viruses.
Elissa D. Pastuzyn, Cameron E. Day, Rachel B. Kearns, Madeleine Kyrke-Smith, Andrew V. Taibi, John McCormick, Nathan Yoder, David M. Belnap, Simon Erlendsson, Dustin R. Morado, John A.G. Briggs, Cédric Feschotte, Jason D. Shepherd. The Neuronal Gene Arc Encodes a Repurposed Retrotransposon Gag Protein that Mediates Intercellular RNA Transfer
James Ashley, Benjamin Cordy, Diandra Luci, Lee G. Fradkin, Vivian Budnik, Travis Thomson. Retrovirus-like Gag Protein Arc1 Binds RNA and Traffics across Synaptic Boutons