Re: What classification has been given to Archaea?

hi Tim,

Welcome to the wonderful world of the Archaea! They are fascinating little organisms.

The quick answer to your question is yes - the Archaea are classed in a kingdom all of their own. First though, let's think about how and why we classify organisms. The main reason is to help us understand how living things are related to each other. These relationships can be quite obvious even if you are not a biologist. For instance, it's obvious that humans are more similar to chimpanzees than they are to birds. Then again, humans, chimps and birds are all animals - they are closer to each other than they are to plants, or bacteria. The study of these relationships is called phylogeny.

You can think of the relationships between organisms as looking like a tree. At the tips of the branches, you find individual species. As you move away from the tips, the branches join into larger branches. In our example above, all of the animals belong to a big branch. Move higher along the branch and the branch splits into "mammals" - here we find humans and chimps, but not birds which are on another branch. Moving towards the tip, the chimps split off on a branch of their own and we are left at the tip of our branch. The problem that biologists have is deciding where the branches should split.

What biologists have done is to create several divisions, each one containing fewer organisms than the one before, until they arrive at individual species. There are 8 major divisions and human beings fit into them like this:

That last one is important, because there are 3 superkingdoms. Eukaryota contains everything from yeast to humans - we look different but our cells are quite similar. Bacteria are separate - they are single-celled and their cells are different enough from ours and those of yeast for them to be classed in a kingdom all of their own. And the 3rd superkingdom - is the Archaea. They are also single-celled, with simple cell structures and in many ways they resemble Bacteria. But when you look closely at their cells, their DNA and their proteins, Archaea are different enough to Bacteria to go in a big group by themselves. In fact in some ways, Archaea are more closely related to you and I than they are to Bacteria!

You can find out a little more about Archaea at this web page. And if you'd like to know more about how we classify organisms, try this Museum of Paleontology or the Tree of Life project.