ASYMMETRIC DIVISION. “With the discovery of aging in single-celled organisms with no clear separation of these two constituents, it has been proposed that reproduction by asymmetric division is a prerequisite for aging and that organisms that reproduce without a distinction between parent and offspring do not age, thus exhibiting functional immortality.”
http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.0030045