Thursday, September 2, 2010


I'm teaching Invertebrate Zoology again this fall, and I intend to blog regularly throughout the term. For starters when I teach this class, before delving into the morphology, physiology, behavior, and ecology of the various groups, I like to think about the larger context and how invertebrates fit into the big picture of life on Earth. One way to visualize this big picture is in a phylogentic tree, which depicts patterns of evolutionary relationships among the groups represented by branches on the tree. This one includes everything from bacteria to people, although it gives short shrift to some important groups, like the Protists, and inflates others. It's odd that the mere 4500 mammalian species take up such a significant proportion of this figure, which represents tens of millions of species, at least. There are fuller treatments of mammalian phylogenic patterns available. Ignoring the bacteria for the moment, this tree of eukaryotes gives a rather different representation of protist diversity relative to the metazoans, which occupy only a modest corner in the lower right of the figure. The textbook for this class presents multiple versions of metazoan phylogeny, and we'll be discussing evolutionary relationships among animal phyla throughout the term.
I love phylogenetic trees and the evolutionary context they offer for considering life's diversity, although there are clearly others who are more committed to this view of the world than I am. This image is from Carl Zimmer's Science Tattoo Emporium, and if you're really excited about scientists acknowledging their passions in ink on their skins, you'll be happy to know there is a book coming out soon.

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