The Tree of Life
It would be great to be young again, but I don't think I would like to retake high school biology.
As best I can recall when I went to school, the so-called Tree of Life was divided into two kingdoms: essentially plants and animals. Of course those were assigned their Latin forms: Plantae and Anamalia.
Then the animal kingdom was divided into phyla, five of them: vertebrates (animals with backbones), arthropods (insects, spiders, etc.), annelids (worms), molluscs (snails, clams, etc.) and nematodes (roundworms).
Further divisions were class, order, family, genus and finally species. In our case, for example, our class is mammalia, our order primates, our family hominids and, finally, our genus and species Homo sapiens.
Even that was enough for me to take the life out of the Tree of Life.
But today things are much more complicated and not only that but nothing seems to be settled. Cladists, people who make decisions about these classifications, seem unable to agree. In fairness to them new information turns up constantly and adjustments must be made to account for it.
And there is certainly plenty to do. Decisions need to be made about the basic tree structure but also about each of its hundreds of branches.
The classification of birds serves as a good example of this. You may wonder why your bird guide makes it so hard to find the species you seek. Even more confusing, why does the order in your new guide differ from the older edition? And specifically, why have the falcons like the kestrel been separated from the other hawks and moved way over between the woodpeckers and the parakeets? When I began birding, the loon was the first species in my bird book and the bluebird was the last. Today geese are first and the house sparrow is last.
All these changes are based on decisions made about characteristics shared by species or groups of species and many of those characteristics today relate to genetic analyses.
But those changes that affect the twigs of the Tree of Life are nothing to those at its roots. The Tree of Life web project (at tolweb.org/Life_on_Earth) has this to say about the current status: "The rooting of the Tree of Life, and the relationships of the major lineages, are controversial. The monophyly of Archaea is uncertain, and recent evidence for ancient lateral transfers of genes indicates that a highly complex model is needed to adequately represent the phylogenetic relationships among the major lineages of Life. We hope to provide a comprehensive discussion of these issues on this page soon."
The wonderful science writer, Susan Milius, discusses the state of this makeover in Science News. "The old tree isn't exactly wrong," she tells us. "The kingdoms that used to crown its top — plants, fungi and animals — still exist. But they've moved. In the new diagram, the tree's former crowning glories shrink to mere side branches, three among hundreds, crowded by the vast diversity of complex single cells. Biologists analyzing this treetop rarely use the word kingdom anymore. They talk of five or maybe seven bigger branches called supergroups. And the story of demoting kingdoms and introducing supergroups is far from over."
Is all this simply an intellectual diversion? Many will consider it, as they do space exploration, a waste of time. But the genetic investigations have turned up odd characteristics like an unexpected chlorophyll component in malaria that will help in the design of future treatments.
More generally, "Knowing that the living world has so much invisible variety can change a person's perspective," says Fabien Burki, one of the genetic pioneers. "The supergroup tree offers the little back-of-the-neck shiver-thrill of realizing that every tomato patch, termite gut or beach bucket of seawater holds life much vaster and stranger than imagined."
So let me trace us humans up through classification as it stands today: sapiens, Homo, Hominidae, Catarrhini, Primates, Eutheria, Mammalia, Therapsida, Synapsida, Amniota, Terrestrial Vertebrates, Sarcoptrygii, Gnathostomata, Vertebrata, Craniata, Chordata, Deuterostomia, Bilateria, Animals, Eukaryotes, Opisthokonts.
Communicating all that to high school students seems to me like asking them to remember pi to fifty digits. Making sense of it will be a still greater problem. I wish their biology teachers well.-- Gerry Rising