User blog comment:DirgeOfCerberus111/Cool Mutations/@comment-3341288-20110804002649

Here is another one. The Chapter's geneseed stores, in addition to everything else, the genetic memory of the previous Space Marines. But the geneseed has been tampered with and now this is genetic memory in a para psychological sense (past life regression from genetic material). So, when a new initiate is implanted with the SM organs, he gradually "recalls" the combat experience of the Marines before him. Because of the mutations, the new Marines mature faster, and they require less training and indoctrination - essentially, they gradually "recall" all the skills of their predecessors. On the downside, sometimes the entire personality of the previous Marine would in a way "overwrite" the initiate's own personality. In the best cases, dead Marines would be spookily "reborn" in the new inductees. In the worst cases, the strain of such "possession" would drive the poor guy crazy, and they'd have to be put down. Still, success rate is high enough.