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Author Topic:   Definition of Species
Dr Adequate
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Message 16 of 450 (429198)
10-18-2007 7:53 PM
Reply to: Message 15 by Medis
10-18-2007 6:47 PM


Re: Complexity of an organism
So what should you use instead? That organisms aren't more complex than others, just different from others?

There might be a sense in which some organisms could be said to be more complex than others, but from an evolutionary point of view, yes, that's about right.

I am a vertebrate, a lobster is an invertebrate. I can't see any reasonable biological sense in which one could declare that I am "more complex" than a lobster, we're just different organisms adapted to different environmental niches.


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RAZD
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Message 17 of 450 (429236)
10-18-2007 10:05 PM
Reply to: Message 11 by Medis
10-18-2007 5:48 PM


Re: Complexity of an organism
I'm looking at a wikipedia article right now saying "More complex organisms such as...".

Consider that if evolution from some original population of extremely simple single cell life form has in fact occurred, that we can make a graph of "complexity" along the x-axis and number of organisms along the y-axis ...

... at the start there is a single vertical line at some arbitrary x value we can label "1" and that this is the initial condition.

Any evolution will add some change, some complexity, but to go the other direction - to become more simple - means extinction and that there can be no negative values.

Over time each population of organisms can become more or less complex, but due to the constraints of the graph conditions it would necessarily extend further into complex as time passes.

One can even predict the shape of this curve as it changes from generation to generation with the assumption that the change in each population is random (more, same, less complex) subject to the constraint for x to be positive. This would predict that single cell life vastly outnumbers multicellular life, and in fact it does.

Thus increased complexity is a natural result of prolonged evolution, but not a required one - the cyano-bacteria again show it is not necessary.

Enjoy.


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This message is a reply to:
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Medis
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Joined: 10-16-2007


Message 18 of 450 (429302)
10-19-2007 4:42 AM
Reply to: Message 17 by RAZD
10-18-2007 10:05 PM


Re: Complexity of an organism
How do you define complexity then, RAZD? Dr Adequate doesn't seem to acknowledge such a thing, so what's your definition.

Edited by Malangyar, : No reason given.


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RAZD
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Message 19 of 450 (429328)
10-19-2007 8:20 AM
Reply to: Message 18 by Medis
10-19-2007 4:42 AM


Re: Complexity of an organism
There is no good definition for complexity for use in biology that I am aware of. From dictionary.com we get:

http://dictionary.reference.com/browse/complexity

quote:
noun
1. The quality or condition of being complex.
2. Something complex: a maze of bureaucratic and legalistic complexities.

noun
the quality of being intricate and compounded; "he enjoyed the complexity of modern computers"


with complex defined as

quote:
adj
1.a. Consisting of interconnected or interwoven parts; composite.
- b. Composed of two or more units: a complex carbohydrate.
- c. Consisting of at least one bound form. Used of a word.
- d. Consisting of an independent clause and at least one other independent or dependent clause. Used of a sentence.

2. Involved or intricate, as in structure; complicated.


So at a most simple level an organism with two cells is more complex than a single cell organism, even if they are a colony of similar cells.

We can also have a population of organisms with a variety of different mutations (alleles) providing genetic diversity within the population. The "complexity" of each organism can be the same, but the "complexity" of the population is greater due to the variations.

Dr Adequate doesn't seem to acknowledge such a thing, ...

It's more that this is a relatively meaningless issue in evolution, as there is no way to compare the "complexity" of a cat with that of a dog.

No matter how you define it you have the same pattern of general increase over time but no specific pattern for evolution in one direction or the other.

And there is the issue of how "complex" multicellular life is when you compare cells to single cell life.

Enjoy.


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RAZD
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Message 20 of 450 (434107)
11-14-2007 3:07 PM
Reply to: Message 1 by RAZD
09-09-2007 5:26 PM


numbers game
U of Michigan Lectures - The Process of Speciation

quote:
Biological species concept: This concept states that "a species is a group of actually or potentially interbreeding individuals who are reproductively isolated from other such groups."

Morphological species concept: Morphology refers to the form and structure of an organism or any of its parts. The morphological species concept supports the widely held view that "members of a species are individuals that look similar to one another."


http:///WebPages/Glossary.html#S

quote:
... some definitions can be combined into the concept that a species is a population of individuals bearing distinctive genes and gene frequencies, separated from other species by biological barriers preventing gene exchange.

http://www.allenpress.com/pdf/mamm-87-04-24_643..662.pdf

quote:
We define a genetic species as a group of genetically compatible interbreeding natural populations that is genetically isolated from other such groups.

{ramble}

Wouldn't it be easier to use genetics to define a species similar to the morphological definition, as "a population of individual organisms with 99% identical DNA" for instance?

What about: "a species is a population of individual organisms with similar hereditary traits in common, separated from other species by different hereditary traits and biological barriers preventing breeding."

In both cases it comes down to how much needs to be the same and how much needs to be different to differentiate one species from another.

{/ramble}

Enjoy


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RAZD
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Message 21 of 450 (493600)
01-09-2009 7:31 PM
Reply to: Message 20 by RAZD
11-14-2007 3:07 PM


bump for westernjoe
in Message 20 westernjoe wails

I dispute this because you don't even know what a "species" is. Darwinians call different varieties of finches different "speices" yet most of them can interbreed and produce viable, fertile offspring. Same with different varieties of bears. The polar bear and brown bear can produce fertilie offspring as well, yet' they're labled different "species." Finally, your statement is assuming that the "speciation" process happens via the mechanism propped up by darwinists.....which is "changes in gene frequencies over time." This, as well, I dispute and you are welcome to show me an example showing otherwise.

Aside from the issue that the process of speciation does not depend on a definition of species, you are free to discuss the definition of species here.

Speciation does not depend on a definition of species, because it is defined as the process where a parent population divides into two reproductively isolated daughter populations, and that this condition is met when daughter populations no longer breed when conditions are otherwise favorable for it.

Curiously the ability of species to reproduce when forced (injected), such as lions and tiger, lamas and camels, dolphins and whales, does not affect the behavior of organisms in the wild, so this is no criteria to invalidate a definition based on this behavior.

I also note that one of the sources you provide for the definition of evolution has this definition of species:

http://www.williamjhudson.net/evolution/glossary.html

quote:
Biological Species Concept: A definition of 'species' as "a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature." BSC applies well to sexually reproducing animals, but not as well to plant life because there is greater gene flow between plant species. BSC is also difficult if not impossible to apply to the fossil record. Fossils are divided into species based on taxonomic classification (similarity of physical characteristics).

Now if you agree with him on the definition of evolution but disagree with him about the definition of species, then it seems that you have a problem.

However, if you read this definition of species carefully, you should note that the reproductive isolation of finches by being on different islands, and the reproductive isolation of bears by being in different locations, does not conflict with their meeting this definition: each one "occupies a specific niche in nature" and each one occupies a different niche.

The reproductive isolation means that they are not sharing hereditary traits that have been adopted by each species via selection in the different "specific niches" they occupy. Such isolation explains, for instance, why polar bears are white while brown bears are not.

Enjoy.

Edited by RAZD, : added material


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RAZD
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Message 22 of 450 (512579)
06-19-2009 8:34 AM
Reply to: Message 1 by RAZD
09-09-2007 5:26 PM


bump for Doubletime
See Message 1 for definitions of species.

Enjoy


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xongsmith
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Posts: 1920
From: massachusetts US
Joined: 01-01-2009
Member Rating: 3.9


Message 23 of 450 (512655)
06-19-2009 5:34 PM
Reply to: Message 22 by RAZD
06-19-2009 8:34 AM


Re: bump for Doubletime
just took a look...

Complexity of a Species, Cx

proposed definition:

Cx = ln( minimum number of bytes to completely describe all the members of the species ),

where minimum number = current ever-changing best compression algorithm result, deployed upon on any complete stream of bytes describing the species.

note that any descriptive additional clauses needed to account for individuals who have been modified by things like getting an ear eaten off or losing a limb to an ice storm or getting the same tattoo as everyone else in the gang or being born with AIDS are NOT included.

but blue eyes/brown eyes/hazel eyes - that sort of thing are included. the iris in fact is probably as complex as a fingerprint, retinal scans are more so, and so on. things that get passed along from generation to generation.

so already, at the human level, just to pick one of the many amazing living things on this planet, this number is huge. hence the logarithm step. True, it thus corresponds loosely to the definition of thermodynamic Entropy, S, but that is a Red Herring.

Evolution does not care about Complexity. never has, never will.

so, in a nutshell, it's the order of magnitude of the description.
now, whether it's useful or not - that is another story.


- xongsmith

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RAZD
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From: the other end of the sidewalk
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Message 24 of 450 (537435)
11-28-2009 3:02 PM


for herebedragons - speciation, definition first, discussion second
See thread above for definitions of species and speciation.

In Message 224 of the Has natural selection really been tested and verified? thread, herebedragons says:

Razd writes:
speciation is where diversity begins, as during speciation events a parent population divides into two daughter populations that become reproductively isolated, stop sharing genetic material, and then evolve along different paths due to different ecologies and selection pressure. The daughter populations become increasingly diverse from each other after the speciation event, for the simple reason that there is no process to make them to be similar.

I also understand that there does not need to be genetic or biological isolation for speciation to occur, only reproductive isolation.

It can be a behavioral change that prevents interbreeding as a pre-mating mechanism. When this occurs the sub-populations no longer see the other sub-population as potential mates, but rather as different species and treat them as such.

Again Razd wrote:
Again, the critical element is whether the populations are reproductively isolated. This isolation can occur pre-mating based on changes to mating behavior.

There have been several examples of human populations being reproductively isolated.

1. Maya Indians - South America from about 2000BC to 900AD.
2. Current populations of indiginous peoples in both South America and Africa who do not breed either by ethnic choices or geographical isolation.
3. Native American Indians - Supposed to have immigrated to North America at least 12,000 years ago and possibly as far back as 50,000 years. Plenty of time to speciate, don't you think?
4. I understand the Ancient Egyptians were isolated for thousands of years (primarily by choice), but I don't have details or references right now.

The difficulty here is that reproductive isolation has not been established, instead we see geographic isolation with the potential to become reproductive isolation. Reproductive isolation is established where populations do not interbreed when they have the opportunity, and it is evident from human experience that this condition is not met.

During those times there was no observed biological evolution to prevent mating (including post-mating infertility or loss of viability of hybrids between varieties) nor was there any behavioral barrier developed to prevent mating. It is possible that some loss in viability occurred between native americans and white settlers, but there is no documentation of increased still-birth rates etc to go on, and certainly since then the genomes have become merged again so that any effect has been diluted by now.

Just these four examples provide plenty of opportunity for human evolution, or more precisely speciation, but has not been shown to have happened. Each of these examples faced vastly different environmental pressures and ecologies. One may argue that evolution has occured, as we have varing skin colors, average heights, limb lengths, facial structures, ect. But none have been classified as a new species.

Correct, variation is observed, there is a difference in the frequency distribution of hereditary traits in the various breeding populations that has occurred over many generations, so indeed evolution has occurred. These changes were not enough to alter behavior of reproduction nor the biology of reproduction, and thus speciation did not occur before the populations were once again merged.

These variations would be enough to classify a new species in Greenish warblers, ...

No, because pre-mating behavior differences were observed to prevent interbreeding in the Greenish Warblers, a difference that was not observed in humans.

... Galapogos finches, ...

Yes and no, because reproductive isolation did occur between some populations of Galapogos finches but there were still some hybrids that were viable, and the isolation observed pre-dated the study so that it was not a part of the observed changes during the study. IOW reproductive isolation was on it's way, but had not been completed, and this isolation was not an aspect of the study of natural selection.

... Peppered moths ...

No, because they are both varieties of the same moth and can freely interbreed. Selection was only on the basis of predator visibility in the different ecologies, and occurred in too short a time, biologically, for the changes to be "fixed" in the genes so that reproductive isolation could result.

... and others.

Reproductive isolation and speciation is established in the Cichlid fishes in Africa and is an observed instance of speciation.

http://en.wikipedia.org/wiki/Cichlid
http://en.wikipedia.org/wiki/Speciation
http://en.wikipedia.org/wiki/Speciation#Sympatric

quote:
The most widely accepted example of sympatric speciation is that of the cichlids of Lake Nabugabo in East Africa, which is thought to be due to sexual selection. Sympatric speciation refers to the formation of two or more descendant species from a single ancestral species all occupying the same geographic location.

In other words, sexual behavior resulted in reproductive isolation, as in the Greenish Warblers, and this resulted in new species. The behavior differences are not limited to sexual behavior, but also affect overall behavior, including where, when and what they eat, and these likely led to the sexual mating occurring in different places and at different times.

I wonder if it is actually a stretch to consider these specimens have truly "speciated".

Only when it is demonstrated that reproductive isolation still occurs when there is opportunity for interbreeding, but it either fails to occur (behavioral) or fails to produce viable offspring (genetic\biological).

And I question the accuracy of taking the above examples and extrapolating them into the following statement:
Razd:
By this means, an arm can develop into a wing, or a skin flap can develop into a gliding surface.

Well, that might be due to the fact that the examples given were to show natural selection in action in the world today, and not long term evolution over many generations.

If you want to look at the long term evolution of species through morphological changes, you need to look at changes that occur over many generations. This has been done with short lived species (fruit flies, bacteria, etc) but not with species who's generation time is similar to humans (~20 years IIRC) making observation over many generations difficult. For this you can refer to the fossil record, and instances like Pelycodus:

http://www.don-lindsay-archive.org/creation/pelycodus.html

quote:
Pelycodus was a tree-dwelling primate that looked A complete fossil much like a modern lemur.

The dashed lines show the overall trend. The species at the bottom is Pelycodus ralstoni, but at the top we find two species, Notharctus nunienus and Notharctus venticolus. The two species later became even more distinct, and the descendants of nunienus are now labeled as genus Smilodectes instead of genus Notharctus.

Here you can see gradual morphological changes occurring over many generations, and you can also see a speciation event occurring over many generations. Similar evolution would develop a gliding membrane from skin, however this would not likely be preserved in the fossil record.

I am still convinced there are "biological barriers" (I am using that term because I don't know how else to refer to it) to evolution. What is the evidence to the contrary? Honestly I still have more studing to do on the Greenish warbler and the Galapogos finches, but as far as I could tell, reproductive isolation is established by social and morphological reason only, not biological.

Morphological IS biological, morphology is due to the phenotype, which is a result of the genotype (genes) and the developmental environment of an organism (and which includes acquired traits).

You can also find instances in fruit flies where the reproductive organs have changed morphologically to where it is not possible for one daughter population to physically mate with the other daughter population.

We also see with horses, donkeys and zebras, that there is a genetic barrier to hyridization that has occurred since they separated from a common ancestor, one that results in infertile or poorly fertile offspring that most ofted die without reproducing, thus demonstrating genetic reproductive isolation being acquired.

Enjoy.

Edited by RAZD, : button too soon hit did I

Edited by RAZD, : top line added


we are limited in our ability to understand
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Replies to this message:
 Message 25 by herebedragons, posted 11-29-2009 9:02 PM RAZD has responded
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 Message 41 by herebedragons, posted 12-22-2009 2:13 PM RAZD has responded

  
herebedragons
Member (Idle past 67 days)
Posts: 1513
From: Michigan
Joined: 11-22-2009


Message 25 of 450 (537633)
11-29-2009 9:02 PM
Reply to: Message 24 by RAZD
11-28-2009 3:02 PM


Re: for herebedragons - speciation, definition first, discussion second
Razd - thank-you. finally a good response from someone! I actually found it by accident as I was looking for another topic since that thread was going nowhere but a bar brawl I will respond after I have time to read the post and the materials carefully.

This message is a reply to:
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RAZD
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Posts: 20323
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.5


Message 26 of 450 (537764)
11-30-2009 7:39 PM
Reply to: Message 25 by herebedragons
11-29-2009 9:02 PM


Re: for herebedragons - speciation, definition first, discussion second
Hi herebedragons, thanks.

I actually found it by accident as I was looking for another topic since that thread was going nowhere but a bar brawl

If you look down the list of topics on

http://www.evcforum.net/cgi-bin/Threads.cgi?action=ta

They are listed by the last post, with the latest post at the top. This is a good way to see what is active.

You can also go down the list and click on the folders to turn off the blue arrows at the left, and then when you come back any topics with new posts will have new blue arrows (your record is now kept with your profile, so it updates your activity, I believe) and this makes keeping track of threads you are interested in easier, as well as lets you know about other active threads.

finally a good response from someone!

I thought of another example where behavior comes into the mix: white-tail deer and mule deer can interbreed and can produce fertile offspring. The problem is that a white-tail runs and jumps from predators, pretty much like a horse, but mule deer use stotting instead: the hybrids try to do both at once with disastrous results.

http://en.wikipedia.org/wiki/Deer#Hybrid_deer

quote:
In captivity, Mule Deer have been mated to White-tail Deer. Both male Mule Deer/female White-tailed Deer and male White-tailed Deer/female Mule Deer matings have produced hybrids. Less than 50% of the hybrid fawns survived their first few months. Hybrids have been reported in the wild but are disadvantaged because they don't properly inherit survival strategies. Mule Deer move with bounding leaps (all 4 hooves hit the ground at once, also called "stotting") to escape predators. Stotting is so specialized that only 100% genetically pure Mule Deer seem able to do it. In captive hybrids, even a one-eighth White-tail/seven-eighths Mule Deer hybrid has an erratic escape behaviour and would be unlikely to survive to breeding age. Hybrids do survive on game ranches where both species are kept and where predators are controlled by man.
(emphasis added)

One would expect the genetic isolation to be growing between these species (and <50% success is already significant), as the hybrids are not likely to survive to breeding when they do occur in the wild, so the chances of gene flow are severely reduced.

Enjoy.


we are limited in our ability to understand
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Stagamancer
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Posts: 174
From: Oregon
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Message 27 of 450 (537893)
12-01-2009 2:49 PM
Reply to: Message 1 by RAZD
09-09-2007 5:26 PM


Why is the definition of species important and what is the use for the definition of species?

The definition of species is important for a few reasons.
1. It is needed for measuring diversity of a community/ecosystem (currently)
2. With many species, it's not a completely arbitrary distinction (mostly sexual species). There are some fundamental biological differences between groups of organisms that are defined as species, and understanding the biological processes that create these distinctions is useful
3. For practical reasons: it's important in the literature that when I say species I mean roughly the same thing as when you say species. Otherwise, we're constantly have to describe in detail exactly what we mean

However, as you've already brought up, defining species is much easier when it comes to sexual organisms that asexual ones. Even if hybrids exist, defining the species is usually not that difficult. The hard part comes with things like bacteria, when it become very arbitrary. Field microbiologists and ecologist often don't use species, they use operational taxonomic units (OTUs) which are defined by an arbitrary cut off of between 80-95% similarity of the 16S rRNA gene. The question really becomes, is species a useful concept for all organisms? I personally think that it is for some, and perhaps not for others. It may be that for asexual organisms, the idea of species is actually not useful, but that doesn't mean we can't use the concept for sexual species.


We have many intuitions in our life and the point is that many of these intuitions are wrong. The question is, are we going to test those intuitions?
-Dan Ariely

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penstemo
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Posts: 13
From: Indiana, USA
Joined: 11-24-2009


(1)
Message 28 of 450 (537998)
12-02-2009 2:04 PM
Reply to: Message 27 by Stagamancer
12-01-2009 2:49 PM


The species concept is very important to taxonomists whose job it is to classify living things. I’ll use plants for examples here because I am most familiar with them but I suspect animals wouldn’t be all that different. Plant taxonomists use differences in morphological characteristics to separate and assign species. Sometimes these differences are quite small and taxonomists are not always in agreement. There are “lumpers” who ignore small differences and assign two or more closely related organisms to the same species while “splitters” would assign each to a different, although very closely related, species.

Collected specimens of dried plants are kept in a herbarium. There are many herbaria, both public and private, in various locations throughout the world. There are one or more specimens of each species designated as the “type specimen”. Curiously, the type specimen need not be typical of the species. But if the original description of the species refers to a particular specimen, that specimen is designated the “holotype” for that species.

There are sets of rules for naming both animals and plants. The International Code for Zoological Nomenclature (ICZN) is a set of rules for naming animals. The International Code for Botanical Nomenclature (ICBN) is a set of rules for naming plants. Both of these have written codes as well as governing bodies that take up taxonomic issues periodically. Just thought I would mention this in case anyone is interested.


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RAZD
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Posts: 20323
From: the other end of the sidewalk
Joined: 03-14-2004
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Message 29 of 450 (538253)
12-04-2009 9:38 PM
Reply to: Message 28 by penstemo
12-02-2009 2:04 PM


cladistic definition of species?
Thanks, penstemo.

There are sets of rules for naming both animals and plants. The International Code for Zoological Nomenclature (ICZN) is a set of rules for naming animals. The International Code for Botanical Nomenclature (ICBN) is a set of rules for naming plants. Both of these have written codes as well as governing bodies that take up taxonomic issues periodically.

I could google them, but I'm lazy tonight: could you provide a link to these standards? It might be useful to outsiders to see what the scientists standards are.

The species concept is very important to taxonomists whose job it is to classify living things.

I'm wondering how much cladistics is having on traditional taxonomy and whether we may end up with a cladistic definition of species? A minimum cladistic group that all members can share some %% degree of similarity and don't have non-breeding members?

Enjoy.

Enjoy.


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This message is a reply to:
 Message 28 by penstemo, posted 12-02-2009 2:04 PM penstemo has responded

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 Message 31 by penstemo, posted 12-04-2009 10:10 PM RAZD has acknowledged this reply

  
RAZD
Member
Posts: 20323
From: the other end of the sidewalk
Joined: 03-14-2004
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Message 30 of 450 (538254)
12-04-2009 9:52 PM
Reply to: Message 27 by Stagamancer
12-01-2009 2:49 PM


Hi Stagamancer,

The definition of species is important for a few reasons.

I've become more of a fan of cladistics as time passes, as it seems to me that:

  • species is the only distinction that matters to the inhabitants of an ecosystem, and
  • family relationships are clear without confusing the issue with what level the dividing ancestor holds in the overall taxon system.

Field microbiologists and ecologist often don't use species, they use operational taxonomic units (OTUs) which are defined by an arbitrary cut off of between 80-95% similarity of the 16S rRNA gene.

That is similar to the genetic species concept in Message 1, using one specific gene. I think I'd want to do some kind of cladistic analysis of more units, perhaps at a chromosome level, and then focus on the one showing the most difference to provide the cutoff information.

This would have to be done first for species that are closely related but just not breeding compatible -- horses/zebra/donkey and whitetail/mule deer -- to see what a genetic level of difference was necessary.

This works for living organisms, possibly for bacteria, but not for fossils.

A cladistic approach to fossils could also generate a measure of how much difference in fossil traits can occur within a species and when that level is passed so that arbitrary speciation can be measured. This would have to be correlated with the amount of changes seen where we have examples on non-arbitrary speciation (as in Pelycodus).

Part of the problem is the degree of dis-similarity that can occur in a species, whether you are a lumper or a splitter, and how good the evidence. Add the ego-boost of being able to describe a new species fossil for the first time, and you can see that defining species for fossils can be a problem.

Enjoy

Edited by RAZD, : /list


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

This message is a reply to:
 Message 27 by Stagamancer, posted 12-01-2009 2:49 PM Stagamancer has acknowledged this reply

  
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