By this logic, transposons have acquired the capacity to self-copy because it improves their prospects of long-term survival. They replicate themselves more quickly than the host genome replicates, and they sometimes jump into other lineages, which enables them to evade extinction with the dying out of a single lineage. As a secondary effect, the redundant DNA that they add to a genome becomes available and might even prove useful, as it mutates, for cellular functions.
