YOUNG MICRO-RNAs. “MicroRNAs originated over different time-scales are often predicted/verified to target the same or overlapping sets of genes, opening the possibility of substantial functional redundancy among miRNAs of different ages. Higher degree of tissue specificity and lower expression level was found in young miRNAs.” (TE = transposable elements; miRNA = microRNA).
http://bmcgenomics.biomedcentral.com/articles/10.1186/1471-2164-13-718