TEACHING ABOUT EVOLUTION AND THE TREE OF LIFE, WITH EMPHASIS ON THE NEW CLASSIFICATION OF THE EUKARYOTES

When teaching the evolution and diversification of eukaryotes, it is helpful for students to have a clear understanding of a recent version of the “tree of life” or phylogenetic tree. The phylogenetic tree helps students see the relationships among diverse types of organisms, which may or may not be reflected clearly by traditional Linnaean taxonomy. The past ten years have seen the complete revision of the classification of the eukaryotes into about six supergroups, using data from gene sequencing and molecular analysis of DNA (molecular phylogenetics). Computers have compared selected genes or the entire genome of many different types of organisms. This classification continues to be refined, but is supported by biochemical data and morphological data from ultrastructural research on cells using electron microscopes. These eukaryote supergroups include the Opisthokonts (Metazoans and Fungi), Archaeaplastida (plants), Rhizaria (foraminifera and radiolaria), Amoebozoa (amoebas and slime molds), Chromalveolata (diatoms, dinoflagellates and coccolithophores), and Excavata (euglenids and others). Further work by researchers has refined this classification and established relationships between some of these groups, and has divided others. Providing students with this information helps them see that the evolutionary relationships between organisms can be demonstrated through the similarity in genetic sequences. It is also helpful to introduce the students to cladistics with some simple classroom activities to construct cladograms for manmade items like coins, or using photos of organisms.