h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Apart from dealing with newly found species, taxonomists must be quite busy checking the validity of 'established' classifications.

How do the traditional methods compare with the newer, genetic based ones?
Have there been many revisions?
If so, are any of them 'big'?
If there are big ones, what are the explanations (suitable for unqualified but interested bystanders)?

Can't remember the specifics but there have been several big revisions in taxonomy. Everything ranging from massive changes to kingdoms, phylums (these ones often back and forth), etc. to people looking at two different texts by two different authors and thinking "wait a minute, this is the same animal".

Well, thirty years ago I was taught that life was divided into two kingdoms, animal and vegetable. Now there are five. Someone correct me on this: animal, plant, fungi, bacteria and multi-celled tiny dudes.

The genetic approach as led to the whole science of cladistics, which analyses things based on how closely they are related to each other rather than their physical traits. This leads to some peculiar findings. For example, since birds are descendants of dinosaurs, and dinosaurs were closer related to crocodiles than either dinosaurs or crocodiles were to lizards, we get the unusual fact that birds are closer related to crocodiles than crocodiles are to lizards. So a cladistical analysis will group crocodiles and birds together, and lizards separately.

Closer to home, we find that the descent of humans has been revised. It used to be thought that some proto-ape divided into two groups, one of which became humans, and the other became chimps, gorillas and orangs. Now we think that the proto-ape split into orangs and proto-ape-2. The proto-ape-2 gave rise to gorillas and proto-ape-3. The proto-ape-3 is the direct ancestor of chimps, bonobos and humans. So chimps and bonobos are more closely related to us than previously thought.

"Someone correct me on this: animal, plant, fungi, bacteria and multi-celled tiny dudes."

Actually, the last one should be single-celled dudes with nuclei (eg Amoeba).

Ten years ago, I learned that that model was outdated, and the five kingdoms had been replaced by three superkingdoms (or domains): Eukarya (cells with nuclei), Bacteria, and Archaea (weirdos). Then in college, my profs chucked this approach and introduced us to clades.

Well now, that's given me some thinks. Thank you, folks.

A comment on 'cladistics':
OED says, in parts,

"It is often..concluded that cladistics carried to its logical extreme..does not provide a suitable basis for classifications, but this is no reason for not considering..cladistic methodology for those things that it can do well." (1969)

"some viruses could be cladistically part insect, part bird and part mammal." (1974)

"Cladistic classification is..inapplicable to non-sexual organisms and will presumably never be used for microorganisms such as Protozoa, bacteria and viruses." (1979)

The entries are 'old' - dating from 1960 to 1982, and their tone is not generally in favour, so presumably things have evolved in that regard...?
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Why is it that I get this feeling that the more interesting things get in science the closer we get to going 'poof' & starting all over again - in the soup?

(quite apart from the increasing difficulty of grasping the gist of things).

Taxonomy is based on the assumption that things are neatly divided into groups, but they aren't. The distinction between species isn't even clear-cut. Look up "ring species" for details. Look up hooded crows and carrion crows, which are separate species but can interbreed and produce non-sterile offspring.

One major rethink (according to RD in 'The Ancestor's Tale'), are the relationships between phyla. Formerly, onycophorans (velvet worms & co) were thought to be sister-phyla to arthropods (insects etc), as were annelids (earthworms), because their body plans are all based on segmentation. However, genetic studies show annelids not to be closely related to the other two*, which was apparently quite a surprise.

I think that overall, the match between fossil and genetic studies is pretty good, it's just the differences are more controversial, and so more illuminating.



*or rather, show that they evolved segmentation independently without a common segmented ancestor.

Here's a link, which shows (I think) the same classification as in TA'sT.

http://whozoo.org/inverts/animalphylo.htm

Thanks, Gnomon.

I took the second(!) in google's list for 'ring species' - salamanders in California. Fascinating. I'd come across separated species before (mountains etc) but not, I think, this.

I'm nearing overload on salamanders - now for crow pie.
Now I *am* overloaded.

OK. There's talk of taxonomy but not of cladistics. They appear to be used synonymously, which I wouldn't have expected in this (presumably strict) context...?

Pedro: You nipped in there while I was reading elsewhere!

Sometimes I sits and I thinks. This time I just sits.

Blimey when I was at uni, not that* long ago I think the kingdoms were, Anamalia, planti, Eubacteria, archibacteria, fungi, protoctista, chromista, and... I think another one Something which phylogenetic studies of relationships amongst organisms/species/subspecies should be helping with is sorting out covergent from divergent evolutionary traits, like with the segmentation and thereby presuming they're all from a common ancestor, because they share a trait, where often the same structual or biochemical traits have arrisen in evolition multiple times, and so don't necessarily share a common ancestor in terms of that trait (though ultimately there is a common ancestor or two of all life with a few possible exceptions, just depends how far back you want to go; Some of the highly preserved in evolutionary terms biochemical pathways can't change much over time as they're highly specific and a chance change in aspects of teh pathway renders the resultant organism well, dead basically; Things like respiratory pathways in metabolism etc., count for the (or at least some of the ) %.5/%1/%2 etc., geenetic simularity between very differnt organisms Wish I could remember any of the specifics of this stuff but think I've evolved into something differnt since I last looked at this (spent many a 'happy'? week studying and researching the phylogenetics/cladistics of slime moulds... happy times Didn't birds undergo a major relassification some time back to put them a lot closer to reptiles? although that might have actually been quite some time ago I forget

I think 2Legs's posting sums up the clarity of taxonomy and cladistics nicely.

Perhaps, then, you'd best blame me?