To be both selfish-DNA and “altruistic DNA” at the same time remains infinitesimal. The same infinitesimal (at the evolutionary scale) transition period exists when a functional copy inserts in a site where it brings some selective advantage, the copy being both potentially selfish and useful. A similar unstable stage probably also exists when species evolve from e.g. parasitism to symbiosis, but does not preclude an operational classification between two non-exclusive categories. As in remark #1, the issue is probably linked to the fact that “selfish”, in the same way as “transposable”, generally also qualifies derived sequences that are not by themselves “selfish” or “transposable”, but exist because their direct ancestors were selfish and/or transposable. Although the reviewer’s remark about the use of the term “architect” is formally exact, we note that similar stylistic effects are common in the literature (Mattick (2001) “Non-coding RNAs: the architects of eukaryotic complexity” EMBO reports 2, 11, 986-991), and our feeling was that our “selfish architects” could not be understood in a different way than e.g. Dawkins’ blind watchmaker. Potentially misleading occurrences of “create” were removed from the text, and we believe that this comment published along with the article will prevent misinterpretation of the title. Reviewer’s response: Concerning the infinitesimal probability for a sequence to continue to be both selfish-DNA and “altruistic DNA” at the same time, BC1 RNA is a counter example. It arose in a common ancestor of rodents via retroposition of a tRNA, has a function in the central nervous system and is the master copy of thousands of ID repetitive elements generated over long time periods. However, as the authors stated above, a few rare integrated copies that happened not to be transcriptionally silent, became master copies of additional sub-families of ID repeats [reviewed in ref. [2], given at the end of this section]. Once more, for class I TEs, it would be the RNA that is selfish, not the bookkeeping DNA [7], just as the RNA of an RNA virus would be selfish and not the integrated genomic DNA copy. On the other hand, DNA transposons (class II) might be considered selfish DNA. Authors’ response: This is indeed a nice counter example. Retroposition ability and cellular function may be both present because the gene is in a transitional stage buy Aprotinin pubmed ID:http://www.ncbi.nlm.nih.gov/pubmed/27735993 before retrotransposition ability be lost, or because both reside on the same sequence in the gene (the nontRNA part). 3) For most investigators, evolutionary considerations begin with the last common ancestor (LUCA) with RNA, protein and DNA already in place. A look at theRNA world and major evolutionary transitions [4], especially those from the RNP world to modern cells with DNA as bookkeeper, provides some scenarios to questions [5-8] such as: “Are we able to understand why they [TEs] are here, and why they are still here?”. This also should qualify the statement, “the Central Dogma could not be questionable”. See ref. [2], Figure 3. Authors’ response: the reference to the Central Dogma was indeed unnecessary here, and we have reformulated this sentence. In order to address a remark from reviewer 1, most open questions were reformulated, so that we could not directly refer here to the origin of DNA. 4) “TEs possess two main characteristics that distinguish them from classical genes…”. One should remind the reader that some TEs are not genes. LINEs and LTR elements are more.
