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Author Topic:   Definition of Species
jar
Member
Posts: 31462
From: Texas!!
Joined: 04-20-2004
Member Rating: 3.0


Message 166 of 450 (572340)
08-05-2010 10:10 AM
Reply to: Message 164 by Big_Al35
08-05-2010 9:43 AM


Re: Species Definition
Big_Al35 writes:

We don't even know if TRex was a top predator or just a scavenger.

And that is related to species how exactly?


Anyone so limited that they can only spell a word one way is severely handicapped!

This message is a reply to:
 Message 164 by Big_Al35, posted 08-05-2010 9:43 AM Big_Al35 has not yet responded

  
Blue Jay
Member (Idle past 982 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 167 of 450 (572345)
08-05-2010 10:31 AM
Reply to: Message 151 by Big_Al35
08-05-2010 6:10 AM


Re: Species Definition
Hi, Big Al.

Big_Al35 writes:

I am not the one advocating the newer definitions of species.

You still haven't convinced me that you even know which definitions of "species" are the newer ones, so I don't yet know how to respond.

I sounded to me like you were clearly advocating a molecular definition of "species."


-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.


This message is a reply to:
 Message 151 by Big_Al35, posted 08-05-2010 6:10 AM Big_Al35 has not yet responded

  
Percy
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Posts: 18870
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.4


Message 168 of 450 (572346)
08-05-2010 10:35 AM
Reply to: Message 162 by Big_Al35
08-05-2010 9:32 AM


Re: Species Definition
BigAl35 writes:

Again I must refer you to a link that I already supplied in another debate about the differences between lions and tigers.

Ok here is one link from potentially many that supports my claim that the differences are hard to distinguish.

I think you will agree that lions and tigers are different species, yet they have almost identical skeletons.

So you think that if we were to dig up fossils of lions and tigers that we might assign them to the same species? While I don't think that would happen with lions and tigers (Wikipedia says they can be distinguished from one another: "However, due to the amount of skull variation in the two species, usually, only the structure of the lower jaw can be used as a reliable indicator of species."), there were probably tons of closely related extinct species that could not be distinguished with only fossil remains. Squirrels come to mind.

Mistaking two different species for the same species happens with living creatures all the time. I presume you don't think it much of a problem for biology when they discovered that African elephants, once thought to be a single species, may actually be multiple species. There's still a debate about this. Yet scientists have no trouble learning a great deal about African elephants.

So why do you perceive it to be a significant problem for learning a lot about, say, T-Rex if we're actually mistaken in thinking our fossils represent a single species? Even if they are multiple species they're still extremely similar.

--Percy


This message is a reply to:
 Message 162 by Big_Al35, posted 08-05-2010 9:32 AM Big_Al35 has responded

Replies to this message:
 Message 170 by Big_Al35, posted 08-05-2010 11:05 AM Percy has responded
 Message 171 by Big_Al35, posted 08-05-2010 11:22 AM Percy has responded

    
Blue Jay
Member (Idle past 982 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 169 of 450 (572354)
08-05-2010 10:57 AM
Reply to: Message 157 by Big_Al35
08-05-2010 8:34 AM


Re: Species Definition
Hi, Big Al.

Big_Al35 writes:

But we can't just make up ad hoc species and lump these fossils under that category. It couldn't be defined as a species under any of our definitions anyway.

They could be defined as a species using the Linnaean and cladistic methodologies.

Linnaean: define by specific characteristics that are regarded as diagnostic.

Cladistic: define by coding a large number of characters, and seeing which organisms cluster into distinct groups on a cladogram.

It sounds like you’re suggesting we pick one method, and stick to it. Then, when that method isn’t useful, we should not fall back on some other, less reliable method, but just leave it undefined.

This leaves us in the uncomfortable position of not being able to organize our information about things on which we can’t do genetic sequencing or breeding experiments.

I don’t see how this could be seen as helpful to science. All indications are that we accomplish more when we initially organize information poorly, and work to improve it over time, than when we refrain from organizing the information at all.


-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.


This message is a reply to:
 Message 157 by Big_Al35, posted 08-05-2010 8:34 AM Big_Al35 has not yet responded

  
Big_Al35
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Posts: 384
Joined: 06-02-2010


Message 170 of 450 (572359)
08-05-2010 11:05 AM
Reply to: Message 168 by Percy
08-05-2010 10:35 AM


Re: Species Definition
Percy writes:

So why do you perceive it to be a significant problem for learning a lot about, say, T-Rex if we're actually mistaken in thinking our fossils represent a single species? Even if they are multiple species they're still extremely similar.

Yes, that's right...there maybe multiple TRex species. I don't disagree that a lot can still be gleaned from the fossil evidence. However, a lot cannot be gleaned from the fossil evidence. eg we don't know if the TRex was a predator or a scavenger. With living species it's very easy...we have access to them and can analyse their behaviour.

We have already discussed three potential definitions of species;
1) genome sequenced definition of species
2) interbreeding definition of species
3) behaviour, diet, appearance, environment based definition.

1 is I believe the newer definition but not yet officially established.
TRex fails to achieve species classification by all three definitions.


This message is a reply to:
 Message 168 by Percy, posted 08-05-2010 10:35 AM Percy has responded

Replies to this message:
 Message 172 by jar, posted 08-05-2010 11:42 AM Big_Al35 has not yet responded
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Big_Al35
Member
Posts: 384
Joined: 06-02-2010


Message 171 of 450 (572361)
08-05-2010 11:22 AM
Reply to: Message 168 by Percy
08-05-2010 10:35 AM


Re: Species Definition
Percy writes:

Mistaking two different species for the same species happens with living creatures all the time.

Yes, and I bet it happens with extinct species even more. When you have two species that are very similar and then discover a third species which is very similar to the other two, it is easy to fall into the trap of suggesting that the new third species is a common ancestor. This may not be true at all. In the case of lions and tigers a new fossil discovery might be a lion, it might be a tiger, it might be a liger or tigon, or it might be a common ancestor. So there is infact more chance of it not being a common ancestor than of it actually being a common ancestor.

I hope you can see where I am going with this. Enjoy!


This message is a reply to:
 Message 168 by Percy, posted 08-05-2010 10:35 AM Percy has responded

Replies to this message:
 Message 174 by Percy, posted 08-05-2010 3:27 PM Big_Al35 has responded

    
jar
Member
Posts: 31462
From: Texas!!
Joined: 04-20-2004
Member Rating: 3.0


Message 172 of 450 (572362)
08-05-2010 11:42 AM
Reply to: Message 170 by Big_Al35
08-05-2010 11:05 AM


Defining fossil critters
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Dinosauria
Order: Saurischia
Suborder: Theropoda
(unranked): Coelurosauria
Superfamily: †Tyrannosauroidea
Family: †Tyrannosauridae
Subfamily: †Tyrannosaurinae
Genus: †Tyrannosaurus
Osborn, 1905
Species

* T. rex (type)
Osborn, 1905

Classifications get increasingly reliable as you move up the ordering while they get more specific (and possibly less reliable) as you move down the ordering.

There is absolutely no doubt that T. rex belongs in these groupings.

Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Dinosauria
Order: Saurischia
Suborder: Theropoda

Now as we get to more detailed classification can there be more mistakes? Certainly.

One such example is being discussed right now. Are Torosaurus and Triceratops actually the same critter but seen at different life stages? Right now the question remains undecided but the evidence is pointing towards the two being the same species.

BUT... we can say the following with a very high degree of confidence.

Classification of Fossil Critters
NameTorosaurusTriceratops
KingdomAnimaliaAnimalia
PhylumChordata
Chordata
ClassReptiliaReptilia
SuperorderDinosauriaDinosauria
OrderOrnithis chia
Ornithischia
InfraorderCeratopsiaCeratopsia
FamilyCeratopsidaeCeratopsidae
SubfamilyCeratopsinaeCeratopsinae
GenusTorosaurusTriceratops?

Note, that it is ONLY when we get to Genus and species that there is a question.

Edited by jar, : trying to get rid of extra space

Edited by jar, : fix sub-title and still trying to get rid of blank space

Edited by jar, : still working on space

Edited by jar, : No reason given.

Edited by jar, : got it. Silly restriction.

Edited by jar, : still fixin

Edited by Admin, : Fix table format.


Anyone so limited that they can only spell a word one way is severely handicapped!

This message is a reply to:
 Message 170 by Big_Al35, posted 08-05-2010 11:05 AM Big_Al35 has not yet responded

  
Percy
Member
Posts: 18870
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.4


Message 173 of 450 (572413)
08-05-2010 3:20 PM
Reply to: Message 170 by Big_Al35
08-05-2010 11:05 AM


Re: Species Definition
Big_Al35 writes:

We have already discussed three potential definitions of species;
1) genome sequenced definition of species
2) interbreeding definition of species
3) behaviour, diet, appearance, environment based definition.

1 is I believe the newer definition but not yet officially established. TRex fails to achieve species classification by all three definitions.

We have no DNA for T-Rex, of course, but why do you believe that T-Rex fails 2 and 3? Even if our T-Rex fossils represent a genus instead of a species, all that means is that there were more than one interbreeding populations of T-Rex, each population sharing the same behaviors, diet, appearance and so forth, and the several populations being more similar to each other than to any other creatures.

--Percy


This message is a reply to:
 Message 170 by Big_Al35, posted 08-05-2010 11:05 AM Big_Al35 has not yet responded

    
Percy
Member
Posts: 18870
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.4


Message 174 of 450 (572415)
08-05-2010 3:27 PM
Reply to: Message 171 by Big_Al35
08-05-2010 11:22 AM


Re: Species Definition
Percy writes:

Mistaking two different species for the same species happens with living creatures all the time.

Yes, and I bet it happens with extinct species even more. When you have two species that are very similar and then discover a third species which is very similar to the other two, it is easy to fall into the trap of suggesting that the new third species is a common ancestor. This may not be true at all. In the case of lions and tigers a new fossil discovery might be a lion, it might be a tiger, it might be a liger or tigon, or it might be a common ancestor. So there is, in fact, more chance of it not being a common ancestor than of it actually being a common ancestor.

Yes, this is true. Because you cannot distinguish close relations from direct ancestors in the fossil record, scientists will almost never claim that some fossil species represents the common ancester for some later species.

I hope you can see where I am going with this. Enjoy!

If you think you're going somewhere other than a dead end, I can only guess that you think our inability to identify specific fossils as common ancestors means that common ancestors don't exist.

--Percy


This message is a reply to:
 Message 171 by Big_Al35, posted 08-05-2010 11:22 AM Big_Al35 has responded

Replies to this message:
 Message 178 by Big_Al35, posted 08-06-2010 5:46 AM Percy has acknowledged this reply
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RAZD
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Posts: 20155
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 4.0


Message 175 of 450 (572442)
08-05-2010 9:09 PM
Reply to: Message 157 by Big_Al35
08-05-2010 8:34 AM


Species Definition vs what matters (and why)
Hi Big_Al35,

Thanks for staying on topic, even if you are making a number of assertions from an under-informed base (not ignorant, but not fully cognizant either):

...I am not a paleontologist or biologist.

And a great way to learn is to ask questions. Hope this isn't too long ...

To the issue of "fish" and "shark" and any other commonly used layman's term for organisms, this is necessarily fraught with misconceptions and mistakes. Taxonomists use many multitudes of measured traits to determining homologous (by descent) versus analogous (derived independently) traits in the formation of trees of descent.

To your basic issue of species definition, there is no single definition that works. Even with DNA sequencing there will be problems, and as you point out, our knowledge of the DNA of fossils is ... slim to none.

But we can't just make up ad hoc species and lump these fossils under that category. It couldn't be defined as a species under any of our definitions anyway. We don't have access to the DNA, we don't know their behaviour and we can never know if they could interbreed. It has become an exercise in futility.

But this assumes that DNA knowledge is critical to determining different species: it isn't. It kind of seems that you want to include DNA in the definition of species, so that then you can claim that species cannot be determined without knowing the DNA. This is employing a logical fallacy in your approach.

The real question is: what matters?

Species labels are useful to human scientists to differentiate bits and pieces of information from the fossil record, from the genetic record, and from the world around us.

Let me introduce the concept of "lumpers" vs "splitters"

Lumpers put lots of populations of organisms into one lumped group and label that a single species, with a number of varieties (slightly different traits, theoretically able to interbreed.

Splitters divide up populations into many small groups and label each one a different species, while the next larger group, genus, incorporates other closely related species that may be able to interbreed but typically don't.

quote:
http://www.zoology.ubc.ca/~irwin/GreenishWarblers.html

Greenish warblers (Phylloscopus trochiloides) inhabit forests across much of northern and central Asia. In central Siberia, two distinct forms of greenish warbler coexist without interbreeding, and therefore these forms can be considered distinct species. The two forms are connected by a long chain of populations encircling the Tibetan Plateau to the south, and traits change gradually through this ring of populations. There is no place where there is an obvious species boundary along the southern side of the ring. Hence the two distinct 'species' in Siberia are apparently connected by gene flow.

Here we have between two and five species (if you're a splitter) and one species with five varieties (if you're a lumper), based on how much you count gene flow through the (small) hybrid zones.

Organisms are generally lumpers compared to humans, relatively unconcerned about what is or isn't a species (it's basically a them kind and us kind approach, although them kind can be broken up into eat this, avoid that, etc). You could call this the "organism definition" of species, and lump a lot of different organisms into big categories. This becomes highly unweildy when populations change from the "eat this" species to the "avoid that" species ... and back.

All the definitions we have of species have similar problems, and this leads to long discussions between lumpers and splitters.

But the point to keep in focus is that they matter to us as a means of describing groups of organisms, and how they fit into the broad scheme of things.

As far as evolution is concerned species is important for two reasons: (1) to define a discrete population (a breeding population) to monitor the process of evolution within the population, and (2) to define when speciation (the division of a breeding population into two or more daughter populations that become reproductively isolated from the others) occurs.

Let me introduce you to the concepts of "arbitrary speciation" and "non-arbitrary speciation" so you can see how this works.

In essence, "arbitrary speciation" occurs when a descendant population is no longer capable of breeding with an ancestral population, however this can end up with an awful lot of species definitions (especially if you are a splitter eh?) -- virtually every other generation. This would get pretty unwieldy very rapidly.

So an arbitrary speciation designation is normally made based on the descendant population at some point becoming as distinguishable from the ancestral population to the same arbitrary approximate difference as exists between two closely related species.

The changes accumulated in the descendant population are similar in degree to the differences between closely related species.

"Non-arbitrary speciation" occurs when two (or more) daughter populations become reproductively isolated from the parent population (as above) and each other, leading to different evolution in different ecologies, and reaching the point where interbreeding does not occur.

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

The numbers down the left hand side indicate the depth (in feet) at which each group of fossils was found. As is usual in geology, the diagram gives the data for the deepest (oldest) fossils at the bottom, and the upper (youngest) fossils at the top. The diagram covers about five million years.

The numbers across the bottom are a measure of body size. Each horizontal line shows the range of sizes that were found at that depth. The dark part of each line shows the average value, and the standard deviation around the average.

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.

As you look from bottom to top, you will see that each group has some overlap with what came before. There are no major breaks or sudden jumps. And the form of the creatures was changing steadily.


Here we have a number of "arbitrary speciation" events, marked by the different species designations along the general trend from lower left to upper right. We also have a couple of instances when the breeding population divides into two groups with a horizontal gap between them, yet overlapping ancestral populations.

These divisions are non-arbitrary speciation events: the two daughter populations after a split are not interbreeding, and this results in the horizontal gap between them.

I have accessed the original article and made the following colored lines on the same basic data to emphasize what is going on:

We see the "drunken walk" of evolution within an overall trend, and if we draw a line down from the left end of Pelycodus trigonodus we see that it is outside the range of traits for Pelycodus ralstoni while a line from the right end up to the top is outside the range for Pelycodus jarrovi.

The divisions of populations like this is evidence of non-arbitrary speciation events in the fossil record even though we do not have DNA samples from any of these fossils.

The staggering along trend that accumulates differences over time, while maintaining overlaps with ancestral and descendant populations shows that arbitrary speciation depends on where you subjectively draw the line, but approximates the same degree of change as occurs between daughter species in non-arbitrary events.

The non-arbitrary events only occur in sexual species, as this depends on the (sexual) biological definition of species.

Arbitrary speciation events would still occur in asexual species, but where you make the differentiation depends on a subjective analysis of when the accumulated changes are sufficient to justify a new arbitrary label for a bunch of organisms in order to describe things.

And whether you are a lumper or a splitter.

Enjoy.


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This message is a reply to:
 Message 157 by Big_Al35, posted 08-05-2010 8:34 AM Big_Al35 has responded

Replies to this message:
 Message 177 by Big_Al35, posted 08-06-2010 5:20 AM RAZD has responded

  
Theodoric
Member
Posts: 6658
From: Northwest, WI, USA
Joined: 08-15-2005
Member Rating: 4.2


Message 176 of 450 (572443)
08-05-2010 9:24 PM
Reply to: Message 162 by Big_Al35
08-05-2010 9:32 AM


Re: Species Definition
I think you will agree that lions and tigers are different species, yet they have almost identical skeletons.

Are you going to transfer this lie to another thread? You have been shown already that this assertion has no basis in fact.


Facts don't lie or have an agenda. Facts are just facts

This message is a reply to:
 Message 162 by Big_Al35, posted 08-05-2010 9:32 AM Big_Al35 has not yet responded

    
Big_Al35
Member
Posts: 384
Joined: 06-02-2010


Message 177 of 450 (572473)
08-06-2010 5:20 AM
Reply to: Message 175 by RAZD
08-05-2010 9:09 PM


Re: Species Definition vs what matters (and why)
RAZD writes:

But this assumes that DNA knowledge is critical to determining different species: it isn't. It kind of seems that you want to include DNA in the definition of species, so that then you can claim that species cannot be determined without knowing the DNA. This is employing a logical fallacy in your approach.

I think it's fair to say that species cannot be determined unless you know their DNA. All the other criteria for determining species can only give best guesses. Maybe DNA is also a best guess.
Lions and tigers could be classed as the same species as they can interbreed and produce fertile female offspring. They could be classed as different species as they have different behaviour, appearance and environment. The only way to clearly identify the distinctions is to investigate the DNA. Ofcourse this doesn't mean that we shouldn't analyse the other differences aswell but DNA would spell out those differences. eg there are genes for coat colour, behaviour etc.

For extinct species we need a system too. Maybe the existing system is adequate. I don't know the details as I am not a paleontologist.


This message is a reply to:
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Replies to this message:
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 Message 203 by RAZD, posted 08-06-2010 6:59 PM Big_Al35 has responded

    
Big_Al35
Member
Posts: 384
Joined: 06-02-2010


Message 178 of 450 (572476)
08-06-2010 5:46 AM
Reply to: Message 174 by Percy
08-05-2010 3:27 PM


Re: Species Definition
Percy writes:

Yes, this is true. Because you cannot distinguish close relations from direct ancestors in the fossil record, scientists will almost never claim that some fossil species represents the common ancester for some later species.

So when I hear suggestions that fossils like 'Lucy' and others are potentially common ancestors I can promptly ignore these??


This message is a reply to:
 Message 174 by Percy, posted 08-05-2010 3:27 PM Percy has acknowledged this reply

    
caffeine
Member
Posts: 1702
From: Prague, Czech Republic
Joined: 10-22-2008
Member Rating: 2.9


Message 179 of 450 (572477)
08-06-2010 5:48 AM
Reply to: Message 170 by Big_Al35
08-05-2010 11:05 AM


Re: Species Definition
Yes, that's right...there maybe multiple TRex species. I don't disagree that a lot can still be gleaned from the fossil evidence. However, a lot cannot be gleaned from the fossil evidence. eg we don't know if the TRex was a predator or a scavenger.

As I already pointed out upthread, this isn't true. Evidence of both scavenging and predatory behaviour has been found for tyrannosaurids, which makes sense as most carnivores do both.

But I'm not sure why you think this is significant for species classification. There are all sorts of unanswered questions about the beahviour of living animals. It's a matter of debate whether honey guides lead honey badgers to bee hives - nobody knows for sure. Does this mean we should be dubious about its species classification?


This message is a reply to:
 Message 170 by Big_Al35, posted 08-05-2010 11:05 AM Big_Al35 has responded

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Big_Al35
Member
Posts: 384
Joined: 06-02-2010


Message 180 of 450 (572480)
08-06-2010 5:59 AM
Reply to: Message 174 by Percy
08-05-2010 3:27 PM


Re: Species Definition
Percy writes:

Yes, this is true. Because you cannot distinguish close relations from direct ancestors in the fossil record, scientists will almost never claim that some fossil species represents the common ancester for some later species.

Here is a link to show that others don't share your view.


This message is a reply to:
 Message 174 by Percy, posted 08-05-2010 3:27 PM Percy has responded

Replies to this message:
 Message 185 by Percy, posted 08-06-2010 6:39 AM Big_Al35 has not yet responded
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