Clades

[Simpo Two]

I came across the word 'clades' as a taxonomic term.

With a biology degree on the CV I thought I'd heard all taxonomic terms, so I googled it...

'a group of organisms believed to comprise all the evolutionary descendants of a common ancestor.'

'What is an example of a clade?
Clade Definition, Uses & Examples | Study.com
An example of a clade is the primates clade. This clade contains extant species such as: humans, apes, new world monkeys, old world monkeys, lorises, and lemurs.'



So why not just call them primates?

[Simpo Two]

Hmm. I'd have thought taxonomy is taxonomy - ie a tree. From that ot seems perfectly clear what is related to what and what descends from what.

What does 'cladistic taxonomy' add? You already know all the primates are related, that's how it works...! Is it a new term? 'Primates clade' just seems to be adding a word for the sake of it...

[Simpo Two]

Hmm. So this is to Darwin as calculus is to arithmetic...

[Simpo Two]

QJumper said:

Looking at it from a laguage perspective, rather than an evolutionary biology one, it makes sense.

Thay are called primates, but primates is just one of many clades. So you need a common term that applies to each grouping.

Take this question for example: "Which clade do chimpanzees belong to?"

Without the word clade, how would you expess that question using just one unambiguous word instead of clade?

And what is the answer? All of the below could be a 'clade' it seems, it just depends how high up you draw the line:

Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Hominidae
Genus: Pan
Species: troglodytes

[Simpo Two]

Thanks for the explanation. It sounds akin to phlogiston to me - in other words a nice idea based on observations but that actually occludes the true picture. Clades should have been thought of in about 1600, then Darwin would have cleared it all up later. As he did, with a bit of help from Linnaeus.

[Simpo Two]

profpointy said:

Not quite sure which way round your comparison is with phlogiston, but if you are suggesting the old naming was analogous with phlogiston, and the oxygen theory is a bit like clades, then there's something in that analogy

To be fair to traditional taxonomy, unlike phlogiston, it isn't flat out wrong, but merely slightly unhelpful

On the contrary, I find 'traditional taxonomy' scientifically accurate and constructive, and 'clades' the sort of thing that might have been thought of before it existed - in other words a loose grouping of organisms based on certain shared characteristics. For example octopuses have an eye structure remarkably like humans, so they must be closely related, when in fact it's an example of convergent evolution. We could also have a clade for organisms that eat only plants, meaning that sheep and blue whales are in the same clade. I don't think that's helpful.

I'd be interested to know which part of traditional taxonomy is wrong. Is it too hard to understand with too many long words?

profpointy said:

Re: phlogiston. As a major digression, some 30 plus years ago I applied for a teacher training course (for science). At the interview the lecturer passed out a paper he'd written on the difficulties of explaining combustion to kids and he had an easier to understand model. His explanation may have been easier to understand, but it was utter bks and more or less the phlogiston theory. I did wonder if it was a test and the "correct" response was to say "this is a load of shyte. You can't teach 'em that" but I didn't risk it so instead was suitably non-committal saying it was "interesting". " I was offered a place but, wisely as it turned out, stayed in IT.

What was the lecturer's version of combustion? Slightly in his defence simplifications have to be made according to the age of the pupil; you can't expect a 10 year old to understand Fermat's theorem. The trick I guess is making something simpler to understand without going too far 'off piste' and thus causing later confusion. I don't remember learning 'combustion' specifically, but we covered oxidation and exothermic reactions which seemed to cover it quite well. Later you encounter 'oxidation is the removal of electrons' which whilst scientifically correct is harder to envisage.

The evolution of science is a fascinating subject. 'The Lunar Men' by Jenny Uglow is a good read.

Edited by Simpo Two on Tuesday 13th February 09:56

[Simpo Two]

Silvanus said:

I thought clades grouped animals with shared evolutionary ancestry, not shared characteristics. A human and an octopus wouldn't be the same clade because of similar eyes.

Exactly my point. Taxonomy groups - or shall we say places in an evolutionary line - animals with shared evolutionary ancestry. If something is later found to be incorrect in the light of new evidence, it's modified. I'm a primate. I know my place

Silvanus said:

Traditional taxonomy doesn't work well for fish, they are a good example of things being grouped together because of shared characteristics. A shark and a lungfish are both seen as fish, but a lungfish is more closely related to a frog than it is to a shark.

I don't think 'shared characteristics' is a very scientific way of grouping things together. The king crab has an immune system remarkably like ours so it's used for research - but we are not actually closely related to king crabs.

[Simpo Two]

profpointy said:

Re phlogiston digression.

I do, and did back then, get that you have to simplify explanations for kids, particularly for chemistry. But whilst I can't remember exactly what was written in a paper I skim read nearly 40 years back, it was more akin to "simplifying" the extinction of the (non-avian) dinosaurs by saying they drowned in the flood, than a legitimate leaving out excess complexity. Phlogiston theory, is flat out wrong rather than a simplification, albeit a good try for the day.

A good point. It just seemed to me that 'clades' seemed like an attempt to make sense of something before the actual answer had been found.

ATG said:

Isn't treating cladistics as an alternative to "traditional" taxonomy a false dichotomy? There isn't a single traditional taxonomic method in the first place. We start with attempts to group things that are similar based on observable characteristics, then the idea of evolution takes hold so people start trying to group stuff by ancestry and cladistics is just a version of the latter that is informed with a modern understanding of inheritance and, recently, with the ability to sequence specimen's genomes. If you've got a non-recombinant (mostly) tree structure of stuff to describe, breaking up the structure into complete subtrees is a sensible approach, and you can then talk about the hierarchy of subtrees to which an organism belongs. I like it because it doesn't try to impose an arbitrary tree of kingdom, phylum, ... family ... species on the tree ... mainly because I can never remember the categorisation and get the order wrong.

Yes, you can use the word 'clade' to describe any grouping, and that's what I find weak about it. The contents of my fridge form a clade. Is science any better off for knowing that? If you can give a clade (a random group) a specific name then you're better informed IMHO. But you support my suspicion that 'clades' are used because the more exact terminology is 'a bit hard' so we'll use an easier one. That's not good science.

ATG said:

Most importantly, it doesn't stop people having endless arguments about where species boundaries lie. "This finch is a different species from that finch." "No it isn't." "Yes it is, I discovered it and I'm going to call it "Yo Mama So Fat pyrrhula". At which point the conversation moves to the carpark.

We used the definition that species can interbreed. If you can't make babies with it, it's a different species (and you should probably stop trying!). Within species you get varieties, races and probably other things too.

I imagined myself living in about 1700 and trying to arrange the elements by cladistics. A clade of brown ones, a clade of silver ones, a clade of gases, a clade of ones that smell. But then Mendeleev and Dalton came along and sorted them all out properly

[Simpo Two]

Super Sonic said:

Clade is nothing to do with similar characteristics, it's all about common ancestors.

Well, me and my cat - currently on my lap - are a clade. We have common ancestors.

I'm not sure how that advances the cause of science though.