MicroRNAs are short RNA molecules that regulate gene expression, for example, by binding to messenger RNA molecules which otherwise would code for a protein at a ribosome. MicroRNAs were first discovered in the 1990s but a full understanding of their numbers and distribution across different tissue types has been slow in coming. Increasingly MicroRNAs are understood to be lineage-specific and a new studyfurther confirms this. lineage-specific structures are the antithesis of evolution and its expected common descent pattern. Instead, structures appear in a few species, or even in just a single species, and are nowhere else to be found. Biology, as John Ray found three centuries ago, is full of unique solutions. Read more