Thoughts on trees and classification.

Posted by Mrs. Kite | Posted in , , , | Posted on Friday, June 03, 2011

You might remember this post: how?
It's was written last semester as I was in awe about my broken paradigms and new thought-trains.
Curiously enough, I left those thoughts resting for a while, and now they return with new teeth, to mess my head again. I don't need to tell you, my dear Penguin about all the details again, and I don't want to bore whoever is reading this with my career rants today. Perhaps next week I will. In summary you just have to add how? + Math: not for dummies . (we're always touching by underground wires, you said xD)

My point is: I have learned a lot about Systematics this year.
I encourage you to search in google images 'phylogenetic tree'. (I am not familiarized with how the order of the search results appear in google, but nevertheless...) the first result I get is this (lets call it 1), then a rather childish drawing I will decide to ignore. Then this (we'll call it 2), then 3 very similar others, and then this (3).
I would need some more information about how each one is constructed, but apparently, none of this is actually a phylogenetic tree. Sigh. I'm serious.
1 caught my mind today, and it's the one I do have information on, so we'll leave it to the end.
2 is (by drawing) a phenogram. (It's missing some important things but the drawing style is totally phenetic) A phenogram is built based on similarities or differences of organisms. From the phenetic school, developed in the 60's-70's mainly by Sneath and Sokal. It does not intend to reproduce evolutive history, it is an artificial criteria.
3. (same as 2, I would need more information but by drawing) it is a cladogram. From (guess..) the cladistics school, developed around the same time that phenetics, mainly by Hennig and De Rosa. It tries to be natural (although they have big internal debates on that) and it is based on homologous charaters.
1. It's a really really famous diagram proposed by Woese. He refers to it as a phylogenetic tree, but if you read Phylogenetic structure of the prokaryotic domain: The primary kingdoms. (Woese and Fox, 1977) you'll be disappointed to find as Table 1. A matrix of association coefficients, used to build... a phenogram. (which I repeat, he referred as a phylogenetic tree, and actually drew somehow as a cladogram, great.)

So, the closest thing we got to a phylogenetic tree is perhaps the childish drawing.

Phylogenetic trees are from the evolutionist school, developed in the 40's mainly by Mayr, Simpson and Huxley. They are interpreted and build in a whole different way from cladograms or phenograms. This would be more like a phylogenetic tree (though AGAIN we would have to see how was it built and all those details that go beyond the drawing)

By taking this class (Systematics I) I really expected to end up understaning how classifications are made (which I think is a complete mess), and to know the infallible method to reconstruct the evolutionary history, turns out: There isn't. Not even our beloved molecular methods (I had hopes on you molecular methods!) So we are left with evolutionism, phenetics and cladistics.

Now I'm looking forward to Biogeography, who would've thought?

Comments (1)

It has been one year of academic differences and you can speak an entire different language already. (not that you couldn't before, this just makes it official of sorts). It makes me happy, seeing the basis being built of what will one day become a worldly-spoken about ziggurat. (too elaborate, i know).

As for the content, I would've never thought of the historic/evolutionary implications of arranging species name in one way or another. (being broad, i know). But it got me thinking how the abstractions we build to discover reality suddenly become immense structures which more often than not overcome our perception of reality.