By Robert Hazen, George Mason University
Molecular phylogeny allows us to look at the DNA of the ribosomal proteins to see similarities and differences between different organisms. So, how does molecular phylogeny work? Does it propose the existence of a shared genetic code?
Certain strands of DNA are common to all living things. For example, there’s a strand that produces ribosomes. Ribosomes are those structures which transfer the DNA information to RNA information, and then convert RNA into proteins directly; and every living thing uses that ribosomal RNA, and uses the ribosomal proteins to create these functions.
But there are subtle differences. From organism to organism, the ribosomes are constructed slightly differently. Through the discipline of molecular phylogeny, we can study the DNA of the ribosomal proteins to compare different organisms. This is true for every kind of organism: from the simplest single-celled organisms, to fungi, to plants, to animals; they all contain the same set of ribosomal proteins.
Molecular phylogeny works by comparing the similarities and differences in certain strands of ribosomal proteins from different organisms. Two organisms that are extremely similar in their proteins are placed close together on this evolutionary tree; two that are very different are placed far apart.
A quite fascinating applications of this phylogenetic approach is actually being used now in linguistics, and in the study of comparative literature.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
Chaucer’s Canterbury Tale
There are 58 hand manuscripts of the Wife of Bath’s Tale, from Chaucer’s Canterbury Tales. What does this have to do with biology, one might ask? It turns out that we can use the exact same approach.
We have 58 handwritten manuscripts, each of which differs slightly from each other, but each of which has basically the same text. None of them is original to Chaucer, none of them is in Chaucer’s handwriting; they’re all copies. Some of them are copies of copies, and thus, we have a chain. However, each time a copy of the manuscript is made, little changes, little errors creep in. Perhaps the copyist thinks that they have a better way of turning a phrase, and so they change it that way. The question arises, then, that out of the 58 copies of this manuscript, which is the most original? Which is closest to Chaucer’s intentions?
Here comes the relevant use of the field of molecular phylogeny. Going by it, every word of all the 58 variants is fed into a computer. The computer then looks for similarities and differences between these different versions of that Chaucer tale. When carried out, it resulted in 58 known manuscripts falling into five main groupings, making it quite clear that certain of those versions were closer to the original common ancestor—that is, Chaucer’s own text, the primary text, which is now lost. One can use these different versions to zero in on what Chaucer actually intended—the original wording of that Canterbury Tale.
A very similar approach was used by Carl Woese, of the University of Illinois
Carl Woese used the phylogenetic approach to focus on the ribosomal RNA and the ribosomal proteins that were common to every organism. This was laborious work; for each organism, one had to extract the genetic material and sequence it so that they have a sequence of letters of A, C, T and G.
They had to feed each of these sequences into a computer for dozens, for potentially hundreds of different organisms; all different kinds of single-celled organisms as well as plants and corn, for fungi; for different kinds of microbes, both eukaryotic and prokaryotic microbes, from hypothermophiles from deep in the ocean to microbes that are common in the human gut. All these different kinds of organisms; for each of them they determine the sequence of this ribosomal protein, and then compare them using computers.
What Woese found was that the genetic diversity among microbes was vastly greater—1,000 times greater—than all of multicellular life combined. It was astonishing that, from this genetic perspective, humans are much closer to mushrooms and to plants, sequoias and so forth, than they are to any of the other microbes.
All of those multicellular organisms form just one little tiny branch at the end of this branching tree of life, but the microbes have incredible diversity. The single-celled organisms, including those with a nucleus and those without, form this vast, branching array. He found that many of the microbes that live in extreme environments are closest to the common ancestor: the first, hypothetical, common ancestor.
The Kingdom of Archaea
Woese proposed that this whole group of microbes be given a new name and be called the kingdom of Archaea. Clearly, this molecular phylogenetic approach not only gives us insights in the evolution of life, but it also gives us some taxonomic information; a new way of organizing life, based on genetics. This is a key way of understanding how life evolved. In this way, molecular phylogeny is then revealing the entire passage of life, and it provides compelling evidence that life has evolved from a common ancestor, over billions of years of life history.
Thus, most definitely it’s the shared genetic code that is highlighted by the study of molecular phylogeny. We can trace the ancestry of all different sorts of organisms by their shared genetic message, the similarities and the differences amongst different organisms.
Common Questions about Molecular Phylogeny and Evolution
Through the discipline of molecular phylogeny, we can study the DNA of the ribosomal proteins to compare different organisms. This is true for every kind of organism: from the simplest single-celled organisms, to fungi, to plants and to animals.
Carl Woese found that many of the microbes that live in extreme environments are closest to the common ancestor: the first, hypothetical, common ancestor.
Carl Woese proposed that the whole group of microbes be given a new name and be called the kingdom of Archaea. Clearly, this molecular phylogenetic approach not only gives us insights in the evolution of life, but it also gives us some taxonomic information; a new way of organizing life, based on genetics.