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Woese's dogma is a fundamental principle of evolutionary biology first put forth by biophysicist Carl Woese in 1977. It states that the evolution of ribosomal RNA was a necessary precursor to the evolution of modern life forms. This led to the advancement of the phylogenetic tree of life consisting of three domains rather than the previously accepted two.

History

Phylogenetic tree of life showing the 3 domains of life branching from the last universal common ancestor (LUCA).

Before the discovery of the archaea, there were only two accepted lineages. The idea of having a third domain of life essentially overturned one of the biggest biological dogma of the time which was the two domains, prokaryotes and eukaryotes. All animals, plants, fungi and certain unicellular organisms were considered eukaryotes, leaving all other microscopic organisms to be prokaryotes. Woese discovered that within the group known as prokaryotes, there were two distinct, unrelated groups of organisms being true bacteria and the newly discovered, archeabacteria. At the time of the discovery organisms considered as archaea were only thought to exist in extreme environments, however in the years later it was realized that they were distributed almost everywhere even in habitats not considered extreme.

RNA as a Precursor

The dogma stated that in order for all the life forms to be discovered, the evolution of ribosomal ribonucleic acids (RNAs) was also necessary. In other words, in order for there to be more specificity within the domains, it was essential that these ribosomes existed. Ribosomal RNA (rRNA) is an essential component for cell, needed in order to make proteins. These RNA molecules are made up of a large and small subunit which go around the messenger RNA (mRNA) as it goes through the ribosome during translation.

Method

Woese's method was quite extensive and time consuming and this is how he was able to identify the three domains of life. He started his research in the late 1960s with the assistance of George Fox. Their first task was to choose a gene of interest which needed to be present in every organism with a high enough turnover rate so that they could track its evolutionary history over generations and generations in order to make a map of how life could have essentially evolved on Earth. The search was narrowed to one molecule of ribosomal RNA, the 16S rRNA in prokaryotes and 18S rRNA in eukaryotes, which is also known as the Goldilocks molecule. This was the chosen gene because of its length, it was long enough to be able to compare to many organisms but not so long that it would be impossible to sequence since the technologies of the time were not very advanced. They sequenced this gene in many different types of organisms one nucleotide at a time by hand, with only a magnifying glass. The intrinsic characteristics of ribosomal RNA were all compared in order to identify and differentiate organisms. After sequencing many types of bacteria, they came across an odd group of prokaryotes which they found to be methanogens. These organisms were distinguished based on their ability to produce methane as they are breaking down food for energy and the fact that oxygen is toxic to them. Once these were eventually able to be to sequenced, Woese realized that its RNA fingerprint was completely different than all of the other bacteria. Woese knew this meant that these organisms could not be bacteria. They may have superficially looked like them, but the RNA didn't have any similarities. In fact, they found that the RNA of archaea was more similar to eukaryotes. They subsequently published their findings in the Proceedings of the National Academy of Science in 1977.

Carl Woese (July 15,1928 – December 30,2012). Image taken in 2004.

This method, has become the standard approach and is very frequently used in biology today but in the past it was seen as radical and not quite the direction other scientists were going in. This same technique used to classify organisms into different lineages is also widely used today in ecology. It allows an entire ecosystem to be surveyed through the collection of rRNA from the environment instead of having to culture the many organisms present in that particular ecosystem.

Controversy

The discovery of this dogma allowed the field of evolutionary biology to go from a concept that was mostly subjective to another type of experimental science which vastly changed the world in terms of scientific research. Woese's dogma is a principle that can be applied in many branches of science such as microbiology, medicine, and ecology as previously stated. This discovery however, was quite startling for most people and came with a lot of harsh criticism and slander. Woese's reputation damaged to the point where he was no longer invited to scientific conferences and referred to as a "crazy crackpot". It was not actually accepted until about 20 years after when genome sequencing arose and proved how distinct bacteria and archaea were from one another.