Charles Darwin proposed that phylogeny, the evolutionary relatedness among species through time, was expressible as a metaphor he termed the Tree of Life. The modern development of this idea is called the Phylogenetic tree.
MicroRNAs are short RNA molecules found in eukaryotes that bind to messenger RNA to regulate gene expression. A new article in Nature, “Rewriting Evolution,” describes how MicroRNAs are causing problems for the tree of life:
“Tiny molecules called microRNAs are tearing apart traditional ideas about the animal family tree”
“I’ve looked at thousands of microRNA genes, and I can’t find a single example that would support the traditional tree”
“What we know at this stage is that we do have a very serious incongruence”
“It looks like either the mammal microRNAs evolved in a totally different way or the traditional topology is wrong.”
The main problem seems to be in the phylogeny of placental mammals, as new phylogenies based upon microRNAs suggest “the tree is all wrong.”
The article informs that Kevin Pererson, a leading researcher, has “sketched out a radically different diagram for mammals: one that aligns humans more closely with elephants than with rodents” and says that microRNAs “give a totally different tree from what everyone else wants.”
Casey Luskin, commenting on this article in Nature Article Finds MicroRNAs are “Tearing Apart Traditional Ideas about the Animal Family Tree” says
The problem, as we’ve discussed many times here before, is that the molecular data often conflict with other data used to construct evolutionary trees, called phylogenies. One gene gives you one version of the tree of life, but another gene gives you a different, conflicting version of the tree.
What is clear from the article is that many researchers don’t “want” to have to confront this data. Some assume that the microRNA data must be wrong because it conflicts with the orthodox phylogeny of placental mammals. Some researchers appear to be in danger of throwing out data simply because it conflicts with the perceived evolutionary wisdom.
Debates will continue about the best way to reconstruct evolutionary trees. But perhaps there’s a more fundamental problem.
Maybe the reason that different genes yield different evolutionary trees is because there isn’t a single unified tree of life to be found. In other words, perhaps universal common ancestry is simply wrong.