|Vl. The Archaea: your living reminder|
Knowing the archaea is your living reminder to keep learning
Step by step, you made your way through the foundation articles on this website. You now have a basic introduction to all the kingdoms of life: bacteria, protoctists, fungi, animals and plants. You can see something of their wealth and power. You've read many stories of their interrelationships, their creativity and their cooperation.
When you look around your neighbourhood, are you now seeing those different living beings from every kingdom? Do you notice them in the media: the papers, magazines, television and film?
At the same time, you are also getting a glimpse of some of the processes used by evolution itself. Remember the different components of the two great cell types, the prokaryote and eukaryote? An ancient symbiosis resulted in the creation of the eukaryote cells from the smaller prokaryotes.
But before you get to comfortable with this “just so” story, remember to include the archaea ( pronounced "ar KEE a")
The archaea are unicells first found in the 1970’s in places where no life was expected: in hot springs, deep sea vents, the guts of termites and salt pans. At first they were labeled “extremophiles”: lovers of difficult environments. How could they survive such temperatures, the lack of oxygen or such saltiness and acidity? How did they grow using sulphur or nitrogen? And imagine living beings creating methane?
New millennium sees revolution in thinking about life
By 2000, archaea were found everywhere else too: in the oceans, in soils of every kind and in the guts of other animals including humans. They appear to be ancient inhabitants of the earth. They share many features with bacteria such as loosely organized DNA and growth by division. They have extra rings of DNA (plasmids) and happily share genes with other unicells as do bacteria.
The puzzle about the archaea seems to be “where do they fit?” Answering this is a major debate in biology right now. Understanding what’s involved will shake you out of what you have always heard. You won’t see the world in the same way ever again.
The other side of the debate
But there is another side to this debate. If we are sorting life, how about considering not only the molecular biology but also all fossil records and life-histories too. Nature, with all its processes of selection, works on living beings, throughout each life cycle, on each individual.
Two personalities in the great debate: Woese and Margulis
Mapping these relationships is the crux. Carl Woese, a cell biologist, emphasizes the absolute importance of the three ribosome subunits. He suggests that this information is the key to everything. He believes all the kingdoms should be placed in three great domains, based on these cell types: Archaea, Prokaryote and Eukaryote.This interview with Woese goes into more detail.
So Margulis suggests a different classification system. This one includes the small bacteria and archaea, with their ability to trade genes with each other, in one major group called the prokarya. The other groups, all with their larger cells, their membrane bound nucleus, are under the heading of eukarya. Here would be the protoctists, fungi, plants and animals. This interview with Margulis explains her ideas in more detail.
What they agree on and wonder about
Although Woese and Margulis differ, they agree that the origins of living beings probably involve more than a single common ancestor. In fact, there is likely to be a suite of very diverse ancestors. Some may have died out and only left traces of their existence in the cells of today’s living beings.
Both Woese and Margulis also consider that viruses should fit in the classification somewhere. Viruses can be seen as traces of living beings. They are leftovers after their ancestors economized to such an extent that they didn't even need cells anymore to exist. A virus is simply a package containing DNA. The virus infects a cell by entering it and using their DNA to hijack the cell's living systems, forcing it to produce what the virus needs.
Shaking up everything you know
Knowing about the archaea, you now find that how you thought about the kingdoms and everything else is not set in stone. It’s actually fluid. But you know something of the controversies. You can see that using kingdoms or domains or prokarya/eukarya are all useful labels in their own way for now. They tell you something about how the living beings being classified. But they also tell you a lot about the ideas of the people who use one system over the others.
The value of knowing the kingdoms
Meanwhile, you have to swim with all the inconsistencies and the contradictions. You've got to keep learning. Whatever the arguments, there are still basic cell types. There still are whole groups of living beings with strong similarities in how they live and reproduce. Each of these contrasts with other groups.
Now for the Tangle
All the groups are so tangled together that there really is no way to separate living beings into a hierarchy or ranking system. What can make any group more important than another?
Knowing the Archaea is your living reminder to keep learning
We welcome your comments! What do you think?
Here is a challenge. Right in your local neighbourhood, “adopt” a kingdom or a domain or any member in these groups. Tell us -- which one do you choose? What more do you want to know about them?