Tetrapods, species selection, and extinction

ResearchBlogging.org

Just a couple of days ago I mentioned the Annual Review of Ecology, Evolution, and Systematics. They must have heard me because today I get my email notification that they have published this year's volume. I'd like to mention three papers of interest to me. Alas, children, if you don't have a library subscription (or a personal one), you won't be able to access these papers directly...

To start with the last one first, here's a paper (Coates et al.) that discusses the history and biology of the relationships of early tetrapods - organisms with four limbs, backbones, and bony skeletons. We are tetrapods, so it's of interest to us in general. One of the interesting things I learned from this is that while the "fish-to-amphibian" transition, of which Tiktaalik is such a great example, occurred in the late Devonian, between 375 and 350 million years ago, the radiation of the modern groups of tetrapods occurred during the later early Carboniferous. See the picture below.

i-e9dc1337fe50f136a689e0c7288c17e9-tets.png

Our next paper is by David Jablonski on species selection. I have always been very skeptical of species selection, although if that merely means species sorting, then I have no objection. Selection is a sorting process in that it sorts varieties in a population to some equilibrium, but not all sorting processes deserve the name "selection". Species sorting is fine - some species have generic properties (like range or rate of repopulation) that make them more likely to persist over evolutionary time - but species selection implies that there is a population of species with varieties within them that are competing at the species level (i.e., not just the aggregate of all the organisms within the species) for some resources. I fail to see how that can occur except in exceptional cases (many little species in a single domain, for example). Jablonski discusses this admirably. I can almost forgive him for using the meaningless term "emergent properties" when he means "group properties".

Our final paper (Purvis) discusses the use of phylogeney in assessing rates of extinction. He discusses a method of using phylogenetic diversity to measure mass extinctions, employing Dan Faith's Phylogenetic Diversity measure. Since this is a highly controversial measure of biodiversity, expect that there will be disagreement about this. But it at least offers an objective metric of extinction rates, even if some think it doesn't deliver...

There are many more excellent papers, not mentioned here only because they aren't in my narrow focus.

Michael I. Coates, Marcello Ruta, Matt Friedman (2008). Ever Since Owen: Changing Perspectives on the Early Evolution of Tetrapods Annual Review of Ecology, Evolution, and Systematics, 39 (1), 571-592 DOI: 10.1146/annurev.ecolsys.38.091206.095546

David Jablonski (2008). Species Selection: Theory and Data Annual Review of Ecology, Evolution, and Systematics, 39 (1), 501-524 DOI: 10.1146/annurev.ecolsys.39.110707.173510

Andy Purvis (2008). Phylogenetic Approaches to the Study of Extinction Annual Review of Ecology, Evolution, and Systematics, 39 (1), 301-319 DOI: 10.1146/annurev-ecolsys-063008-102010

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OK, you obviously have no biological sense, species is real - its called genetic variation within a species - and some "genes" (actually alleles - different types of a gene at one location in the entire genome) make an individual more or less fit than the rest of the species to survive. If this individual does survive, pass on that allele to its offspring (sometimes that doesn't happen cause a parent only passes half the genome on - that is one copy of the two alleles of every gene), and then that offspring continues to pass on the allele to more offspring, and so on, a new species emerges. It will find its own niche (little job to do in nature different than every other species) so it can get what resources it needs to survive - or out compete the old species and cause it to die out and go extinct....

I wish every moron with a computer couldn't write blogs cause you shouldn't write about things you don't know about...

Wow.

I wish every moron with a computer couldn't write blogs cause you shouldn't write about things you don't know about...

The same could be said for drive by commenters who are full of themselves after passing Gr 8 science. Keep studying, Joe, you'll catch on. Try to work on your reading comprehension while you're at it.

Just think John, if only you had met Joe earlier, you could have saved yourself all the bother of writing that book and spent your time more profitably riding your bike, drinking beer, throwing prawns on the barbie...

I think The Moron with a Computer would be a great name for a blog.

Joe, there's so much hand-waving in your post I can't see the blackboard...try thinking it through again. Slowly, in your case. You'll see that all you've described is something we call reproduction. The emergence of a new species is most complex and subtle, my boy. Perhaps---take a class? Read a book? Go back to college? Do that for a while, then you can post on the blogs of people who read _Nature_ for fun.

By kraftytrilobite (not verified) on 16 Dec 2008 #permalink

I make it a rule never to eat anything that wears its skeleton on the outside.

I didn't say you should eat them, John, just throw them on the barbie!