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Author Topic:   What is a "kind"?
Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 12 of 42 (528434)
10-06-2009 5:36 AM
Reply to: Message 11 by Peg
10-06-2009 5:31 AM


You know tarantula and black widow spiders can't reproduce together, right?
You tell me what a species is currently defined as.
There is no single, clearly defined and universally applicable definition of what a species is.

This message is a reply to:
 Message 11 by Peg, posted 10-06-2009 5:31 AM Peg has replied

Replies to this message:
 Message 16 by Peg, posted 10-06-2009 5:50 AM Dr Jack has replied

  
Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 15 of 42 (528437)
10-06-2009 5:50 AM
Reply to: Message 13 by Huntard
10-06-2009 5:39 AM


The Biological Species Concept is not what species mean
Creatures that interact together in the wild, and can interbreeed and produce fertile offspring.
This is the Biological Species Concept, and it's a very good working definition for the tiny proportion of life we can apply it to: that is, to extant life which reproduces sexually and does not readily hybridise - in other words, to a subset of animals, a few plants and some fungi. And even among these it's more a theoretical one that a practical one: it's just not workable to reliably test it in the field for the majority of species.
As you rightly point out it's useless for bacteria; add to that Archaea, the majority of single cellular eukaryotes, and many multicellular eukaryotes and, of course, it can't be applied at all to any extinct organisms.

This message is a reply to:
 Message 13 by Huntard, posted 10-06-2009 5:39 AM Huntard has not replied

  
Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 17 of 42 (528439)
10-06-2009 5:55 AM
Reply to: Message 16 by Peg
10-06-2009 5:50 AM


Peg writes:
why do you think that is the case?
Do you mean why do I think that is the case? (i.e. what sources and ideas lead me to that conclusion?)
Or do you mean: what is the cause behind the fact there is no single, clearly defined and universally applicable definition of what a species is?

This message is a reply to:
 Message 16 by Peg, posted 10-06-2009 5:50 AM Peg has replied

Replies to this message:
 Message 18 by Peg, posted 10-06-2009 6:19 AM Dr Jack has replied

  
Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


(4)
Message 20 of 42 (528457)
10-06-2009 8:19 AM
Reply to: Message 18 by Peg
10-06-2009 6:19 AM


The problem of species
The concept of a species predates Linnaeus, as does binomial naming, but he was he who formalised them and grouped them into Genera, Families, etc. in the familiar system that we still use today. Unfortunately, this system was defined before microscopy, before Darwin's theory of evolution, before Watson and Crick's discovery of DNA and otherwise before the rise of modern biology. It is concept from an age when it was thought that species were the eternal, unchanging creations of God.
We continue to use it because having a grouping for very similar organisms is useful in all sorts of ways and many, many attempts have been made to formalise the concept. They've all failed. The most successful is the Biological Species Concept (BSC), which was originally formulated as "are the same species if they can produce fertile offspring" but later modified to "do so in the wild"1. The BSC has proved an extremely powerful tool for distinguishing species - so much so that many people think it is the definition of species - but it can only be applied to a tiny proportion of currently living organisms.
The vast majority of reproduction on this planet is asexual: all bacteria and all archaea reproduce this way (and just to make things worse they go in for large amounts of horizontal gene transfer) then there's the many eukaryotes that reproduce asexually, both single cellular and multicellular. If things don't reproduce sexually, then the BSC simply can't be applied to them. Most things that have ever lived are now dead, and worse most types of things that have ever lived are now dead. There are countless species that we only known from the fossil record. The BSC cannot be applied to any of the species, because we have no way of telling what they could or couldn't breed with.
So having ruled out the extinct and the asexual, we're left with a small portion of the things we'd like to group into species, probably less than a hundredth of one percent of all living things. But, hey, these species include the big, familiar stuff so that's okay, right? Well.. kinda. Even among the organisms we're familiar with the BSC is hard to apply - you can't, for example, define something as a new species based on a few dead examples or a bit of videos you need to study live specimens in the field, or better yet gene screen a goodly sample - and doesn't actually work all that well anyway. Plants, especially, are particularly fond of forming viable hybrids with different populations we'd really like to describe as different species, and even among the animals creatures like butterflies are alarming fond of merrily hybridising away.
And then you get the crazy edge case hybrids, fish like Poeciliopsis monacha-lucida which is formed by hybridisation of a female P. monacha and a male P. lucida. P. monacha-lucida can viably breed with male P. Lucida but no crossing over occurs, instead the offspring inherit their maternal genome exactly as passed down from the P. monacha, freshly combined with the new chromosomes from the P. lucida sperm. Even whackier is the Amazon molly Poecilia formosa, formed by hybridisation of P. latipinna and P. mexicana. It has to mate with a male Poecilia sp. but the genetic material from that "father" is entirely discarded and the offspring is a genetic close of the mother. Are these separate species? If not, which species are they? Are they truly a viable hybrid with their crazy forms of reproduction2?
I've concentrated on the BSC here, because it's the idea most commonly advanced as the species definition but I assure that all the other ideas for a definition have suffered from a similar array of problems. There just isn't a single, universally applicable definition of species; instead what is called a species is worked out by on an ad hoc basis by the scientists working in the field usign an array of different and varied tools and a great deal of debate. This is particularly true for prokaryotes and fossil species.
To me, this is not surprising, because as I alluded to in my introduction, the concept of a species predates modern biology. The simply fact is that in the light of evolutionary understanding the concept of species is a shaky one as best, perhaps applicable if you view a single snapshot of time, but fundamentally flawed on a longer timescale. The features of organisms within a population change over time (as their genes change), in a way that means that had you a perfect record of these organisms lined up in temporal order it would not be possible for you to point to a particular point where they changed from one species to another but if you looked at the ends of the line you'd find two very different organisms. It is this continuity that makes dividing organisms into discrete species a flawed concept3.
So, in my view, species should not be viewed as a real division of organisms but rather as an idealised tool for understanding the diversity of organisms which should be understood as an abstraction.
1 - The Biological Species Concept can be defined extremely formally and precisely in terms of gene flow but I think that's a needless complication here.
2 - If anyone's interested these two forms of reproduction are called hydridogenesis and gynogenesis, respectively.
3 - The same problem occurs on a smaller scale with ring species.

This message is a reply to:
 Message 18 by Peg, posted 10-06-2009 6:19 AM Peg has not replied

  
Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


(3)
Message 25 of 42 (528829)
10-07-2009 6:05 AM
Reply to: Message 22 by slevesque
10-06-2009 12:55 PM


The kind: comedy gold
I am not very familiar with baraminology, but I found this:
Any chance of a source for that, Slevesque?
I think it's wonderful, full of gems showing up what a crazy notion the Creationist kind is. But first, a little preamble on why Creationists have such a notion in the first place.
You'll note I say "Creationist kind" and not "Biblical kind". That's because the Creationist notion of kind is simply not found in the bible, the words used give no indication at all they're intended to be read as a specialised classification of animals. The only reason that Creationists invented the idea was because it became increasingly clear that the idea that you could find all the different kinds of animals known to man onto the Ark, and so, needing a way to circle that square they pretended it meant something special. Couple that to some crazed notion of ultra-evolution and you have the modern notion of kind.
Course, kind does sound a bit silly, and Creationism is nothing if not an attempt to doll up the silly in the trappings of science, so invent a new term "Baramin", and - just to prove Maureen Lipman wrong when she said that having a "ology" meant something - conjour up a new "study" of this invention and call it Bariminology.
And what a shoddy excuse for a thing this bastard child of Apologetics is.
Let's have a giggle:
quote:
For example, fossil and modern equids qualify as a monobaramin (see Cavanaugh et al. 2003).
  —Mysterious uncited source
Now this is special, our Creationist friends are giving up on pretending that fossil horses aren't related to modern horses, and that fossil horses aren't the ancestors of modern horses. Now they're all part of the same "monobaramin". I managed to track down the article mentioned, you can read it here. Just don't drink coffee while you're doing it, you don't want to spray your keyboard.
Yes, ladies and gentle, Hyracotherium, Equus, Miohippus and the rest are all part of the same kind, having experience stunningly rapid evolution including changes in diet, dentition and the number of toes. Oh my!
Oh, and trying to track down that howler from the (Cavanaugh et al. 2003) cite led me to this wonderful gem of a paper. Have a read, try not to laugh.
Yes, ladies and gentleman, these fellas believe that C4 plants evolved from C3 plants within the last 4000 years. In other words, entirely new biochemical and physical organisation has emerged within a "baramin" but remember, boys and girls, evolution can't happen over millions of years. Oh, no, that's just not possible.
So, in summary, kinds aren't Biblical, they aren't well defined, and the "research" into them blithely accepts rapid changes between wildly different species to a degree that even a evolutionist would write off as implausible.

This message is a reply to:
 Message 22 by slevesque, posted 10-06-2009 12:55 PM slevesque has not replied

Replies to this message:
 Message 26 by greyseal, posted 10-12-2009 10:37 AM Dr Jack has seen this message but not replied

  
Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


(1)
Message 39 of 42 (531334)
10-17-2009 4:42 AM
Reply to: Message 33 by Arphy
10-16-2009 7:38 PM


Re: The kind: comedy gold
Arphy writes:
The point remains that genomes are degenerating (genetic entropy) and no new information arises.
I've read the papers by your finest Bariminologists, as alluded to by Slevesque. They're a joke. And they most certainly do not represent anything that could be described as degeneration.
They're saying that C4 plants can be descended from C3 plants inside of the same kind. Are you seriously suggesting that having a completely new biochemical pathway, differently localised with specialised anatomically features which provides considerably more efficient CO2 fixation and lower water loss, represents a degeneration, seriously?
Come on.
They're also saying that Hyracotherium, Miohippus, Equus and Plesippus are the same kind, along with all the rest of these. Note the differences in toe number, the differences in size, the differences in dentition, the emergence of a specialised knee joint with remarkable energy efficiency properties, the difference in diet. You think that this remarkable array of changes represents only degeneration? Seriously?
Come on.
Arphy writes:
Both Mr jack's and greyseal's comments seem to show a common misconception that creationists don't believe that organisms change or that these changes can look quite big phenotypically.
No, my point is that what they are proposing is beyond stupid: it's a fantasy. And it shows the incredible weakness of the Creationist position. Originally Creationists held the simplistic fantasy that all the animals could fit on the Ark. But this was shown up as complete absurdity by the sheer breadth of living species and the myth of fixed species blown away by the proponderance of direct evidence for speciation, and the multitudes of transitional fossils. So the idea of a kind was conjured up - along with the pretence that inventing entirely new specialised terms and then acting like that was what the Bible was talking about all along is still "taking it literally". But the kind is stubbornly missing from reality which is why your finest Bariminologists are driven into adopting such absurd positions while continuing to spout nonsense like the huge array of variation they believe has sprung forth with breathtaking speed only represent "degeneration".

This message is a reply to:
 Message 33 by Arphy, posted 10-16-2009 7:38 PM Arphy has not replied

  
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