De novo genes: Paradigm Shift or Molecular Mirage?

It has long been understood that new genes evolve from duplication events and subsequent divergence. Since 2006, however, many studies have argued that entire protein-coding genes can emerge "from scratch" by recruiting "random", non-coding and functionless sequences, contrary to what was thought possible. The hypothesis of "de novo" origination is used to explain why some genes do not possess homologs and appear to be lineagespecific "orphans". Some have been implicated in important evolutionary adaptations. Unfortunately, the new field is marred by theoretical problems, false positives, misleading claims and a failure to validate. Many de novo genes are likely to be derived from diverged fragments of older genes that have since been lost in most lineages or revived in one alone. Instead of scouring genomes for evidence of de novo gene birth, improvements in detection tools and methodologies are now urgently required.