By DAVID A. WILSON
This a tale of how two kingdoms, starting 281 years ago, became three, then five, then expanded to six.
This isn't about kingdoms such as Spain and England. This is about the Kingdoms of Life and whether anyone still understands that science is the constant seeking of knowledge, categorizing that knowledge where possible and testing it against any new information discovered.
We also ask how meaningful a "scientific consensus" really is or if there is ever any such thing as "settled science."
To that end, we may want to explore the history of those life kingdoms.
I was taught in high school that there were two kingdoms of life - Plants and Animals - as determined in 1735 by Swedish Botanist Carolus Linnaeus. By scientific consensus, this became Settled Science.
There were a few "two-kingdom" deniers, but they were considered to be on the fringe of scientific thought. "Peer review" made them irrelevant.
In college, while obtaining a biology degree, I was taught that, "oops, the deniers were right, some life forms don't fit neatly into the two kingdom theory." Suddenly the 1866 theory of Ernst Haeckel, German biologist, naturalist, philosopher, physician, professor and artist, was the correct one.
There were actually three kingdoms of life - Plants, Animals and Protists. This three-kingdom model was, by consensus, settled science.
Of course, there were a few "three-kingdom" deniers, but being on the fringe, they were ignored.
A few years later, as a science teacher, I used the five-kingdom model - Animalia, Plantae, Fungi, Protista and Monera - suggested in 1969 by American Plant Ecologist Robert Whittaker. This, for a time, was an accepted consensus.
While working as a microbiologist, I saw that the classification of life forms by the science of taxonomy had taken a hit with the mapping of DNA, RNA and the Double Helix.
Taxonomy meant defining groups of biological organisms on the basis of shared characteristics. Because of the work of American biologist James Watson and English physicist Francis Crick, genetics and the genomes became the major means of classification of life forms.
The study of genomes contributed to the six-kingdom model proposed by American microbiologist and biophysicist Carl Woese and American biochemist and biophysical scientist George Fox in 1977 - Eubacteria, Archaebacteria, Protista, Plantae, Fungi, and Animalia.
Although this model is in common use today in American schools, it is hardly a consensus, since most other countries teach a five-kingdom model.
To confuse the matter more, in 1990 Woese and Fox proposed getting away from the kingdoms and going to a "Three Domain" model.
So, in 2014,where are we on the categories of life?
No one is really certain how many life kingdoms there are. There may be five, six or eight. There may be Domains and no kingdoms. And how many domains are there? Only three?
The most recent consensus is that the six-kingdom model does not work. But, there is no agreement as to a model to replace it.
This is the scientific method at work. The problem has been defined, information collected, a hypothesis formed and the hypothesis tested.
If the information gathered fits the hypothesis, there is a scientific theory. That theory stands until the latest information collected no longer fits.
At that point, a new hypothesis is developed and put to the test.
Science is a never-ending process of testing theories with the latest information available.
Having a scientific consensus does not make a theory fact. Science, by its nature, must remain theoretical. In reality, science can never really be settled.