An 1879 tree by Ernst Haeckel with a bit of a bias. The true tree of life is trunkless -- more of a shrub of life, really. There's a root, but no apex. If forced to choose one, personally, my money's on Theobroma cacao.
Last time I posted a link to a slide show of beautiful jellies. But I don’t want this blog to be only about eye candy. I want to help you learn about new organisms, the often crazy or amazing ways they make their livings, and no less importantly, how they are related and classified.
Because I hope to make this blog accessible to all sorts of readers, from precocious 10-year-olds on up, I’ve struggled with how to help you learn about taxonomy without making you digest the long lists of incomprehensible names found in abundance on most trees. On top of that, I face the problem that classifications are constantly changing.
The Trouble with Trees
Today scientists classify organisms based on how they are related to one another, but unfortunately, it’s often quite confusing to figure out. Sometimes comparing one trait — say, tentacle length — yields one family tree (often called phylogenetic trees by scientists), and comparing another trait — say, mean number of biologists devoured attempting to study organism — yields a conflicting one. Which is correct? Which traits should you give more weight when constructing the tree you think most likely? This is the problem that has launched a thousand theses. Scientists argue about the true relationships constantly, and the trees are rearranged with every publication of a systematics journal.
On top of that, once scientists started sequencing the genes of different organisms and making trees by comparing them, traditional taxonomies that had been stable for decades or centuries based on body shape, anatomy, or other observable traits were often upended, leaving things in disarray to this day. And finally, the formal names we give ranks above species like kingdom, phylum, class, order, etc., are largely arbitrary, as is the idea that there are exactly seven ranks. There aren’t. The ranks are meaningless as absolute markers, so teaching these names seems to me both confusing and pointless.
And yet . . .
The Learning Tree
Some major groups have remained supported by scientific consensus, and other new groups are settling down. And there are true evolutionary relationships among organisms, and themes within lineages of common descent, though individual species can differ radically from their close kin. Learning the major groups helps keep the dizzying diversity of Earth organized in our brains. Strange new species will no longer float around like stray mental post-it notes, but have a taxonomic hook to hang on when you can say . . . ah, that new creature is an annelid. I know exactly which other creatures it’s related to.
So I’m going to try to start including links to trees with each post. It’ll be up to you to explore them as your fancy strikes you. One site I will rely on heavily is the Tree of Life Web Project. Although the descriptions there are often written by scientists for scientists and will be nigh incomprehensible to the lay person, anyone can look at the trees and get a sense of who is related to who and how. Plus pretty pictures help with scary names. : ) Another benefit to studying these trees is seeing how many different organisms are out there that you will never have heard of, and about which so little is known. Virtually every page contains groups that even I — with six years of higher education in biology and a passion for, shall we say, creative life forms — have never heard of.
So here we go: For jellies and friends, which are contained in a group with the formidable name Cnidaria (ni-DAR-ee-a), you can see the TOL trees here and here and a cuter and more digestible, if less rigorous, tree here. Cnidaria was one of the first animal groups surviving today to split from the rest of the animals — and it shows.
