Tweaking the Tree of Life December 14 2014, 2 Comments
I’ve made a few changes to my Tree of Life and have new files available for free download. The changes are in the prokaryotes and protists. The three true kingdoms, the plants, animals, and fungi are still the same. These changes aren’t large, but they make the chart more accurate and useful.
Perhaps I should start by stating current rules on what constitutes a kingdom. Like any other lineage of life, a kingdom is an ancestor and all of its descendants. Organisms that are not descendants of that ancestor are excluded. That is why the Five Kingdom classification is no longer used. Two of those kingdoms, Monera and Protista, are not valid.
On my prokaryote chart, the only change is in the title. I’ve changed “Kingdom Monera” to “formerly Kingdom Monera” and reduced the font size. I wanted put stronger emphasis on the fact that Kingdom Monera is obsolete. It is no longer accepted by biologists because the two branches, bacteria and archaea, are tremendously different at the cell level. While they may have shared an ancestor very long ago, that ancestor would be the ancestor of all life, not just prokaryotic life.
On my protist chart, I changed both the title and the rhizaria branch. Biologists have good evidence that the rhizaria lineage, the stramenopile lineage, and the alveolate lineage shared a common ancestor more recently than the common ancestor of eukaryotes. The lineage is called SAR, an abbreviation for stramenopile, alveolate, and rhizaria. On the chart, I moved the base of the rhizaria lineage up onto the chromalveolate branch (which symbolizes the common ancestors of stramenopiles and aveolates) rather than showing the rhizaria as equally related to all the bikonts.
There are many uncertainties still in the protists, which are not a kingdom because they exclude the plants, animals and fungi. For convenience biologists group these eukaryotes into the informal group we call protists. There is an overwhelming amount of variety in this hodge-podge of life. When you introduce children to the protists, it is good to tell them that the branches on the chart are just the main branches, the ones with many known members. There are lots of other smaller branches as well. New protists are still being discovered and many that we have known of for years are yet to be studied enough to place them on the Tree of Life.
The Tree of Life gives a good framework for children to use as they address further diversity of life. It’s good to remind them that each of the main branches on the chart holds many other lineages, and life is always surprising us with its endless experiments. No chart will be valid for decades, at least not until we have studied many more organisms and determined configurations of many more lineages.
Happy explorations in life. You can use the comments to ask questions about these changes.