How are sponges an "evolutionary dead end"?

[HelPick2]

Does anyone have an answer?

[Zep]

What do you mean by "evolutionary dead end"?

[Beancounter]

Are we talking the things that live in the sea and you can use in the bath or lawyers?

Edited to add: Sorry, that was facetious and uncalled for. ;) Please continue this sensible discussion.

[HelPick2]

Originally posted by Ixabert
Does anyone have an answer?
How did it come to be that they did not evolve into other animals? for they are quite old. I believe no animal's ancestry goes back to the sponge.

[Soapy Sam]

Ixabert- I take it you are quoting someone. Can you give us the source or context?

I have heard the phrase used before. I think it's a rather loose shorthand for saying that a species or possibly larger taxonomic group has become so perfectly adapted to a particular habitat as to prevent evolutionary radiation away from the niche- the implication being that it's threatened with extinction if the habitat is threatened.

I suppose this might apply to some sponges, but I would not have thought they were generally threatened.

The phrase has a rather teleological ring to it. It's not one I would use myself.

[Zep]

Originally posted by Ixabert

How did it come to be that they did not evolve into other animals? for they are quite old. I believe no animal's ancestry goes back to the sponge. But they DID evolve. Current thinking is that the sponge is right near the base of the evolutionary tree.

http://news.nationalgeographic.com/news/2002/04/0401_0401_shapeoflife1.html

[fishbob]

How did it come to be that they did not evolve into other animals? for they are quite old. I believe no animal's ancestry goes back to the sponge. Sponges are NOT an "evolutionary dead end". Whoever fed you that line had you going. Sponges are well suited for the environments in which we find them. When the environments change, sponge species evolve or become extinct. Many sponge species have croaked off over the ages. Many sponge species are relatively recent. Just like every other collection of organisms. Your family included.

[Correa Neto]

As the man said. I would add that I have serious doubts if one could call creatures that are around for at least more than half a billion years a "dead end".

Simple creatures? Yes. But they evolved to fit a number of niches and were quite succesfull on that.

But we should not assume that all simple lifeforms are "dead ends" or "primitive". That's an anthropic bias, based on the (debatable) concept that we, complex creatures, are "at the top" of the evolutionary tree.

When it comes to evolution, the "winners" are those who survive. And simple creatures (labelled "primitive" or "dead ends") may outlive our species.

[Soapy Sam]

Ixabert- an analogy. I once saw a Roman Legionary entrenching tool in a museum. Alongside it was a WWII U.S. army tool. They were remarkably similar. The reason is that the design was an excellent one for the task, so it had not changed greatly in 1800 years. (The main evolutionary innovation was a hinged , folding shovel blade on the later version).

This might be seen as a design "dead end". In fact it's an indicator of a very successful fit between form and function.

The sponges are a good example of Natural Selection fitting a form to an environment. As Fishbob says, natural selection has continued to improve that design and is still doing so.

Also, please note that because one form may give rise to wildly differing descendant forms , this need not mean that the original form becomes extinct. To say A "evolves into" B is misleading. B may well be descended from A, but modern A(i) , identical to A or nearly so, may continue to thrive as well.

[Rob Lister]

Originally posted by Correa Neto
But we should not assume that all simple lifeforms are "dead ends" or "primitive". That's an anthropic bias, based on the (debatable) concept that we, complex creatures, are "at the top" of the evolutionary tree.


Seems to me we could assume that humans are an evolutionary dead-end, at least in the darwin-sense of the word 'evolution'. The 'evolution' of humans to the next step might likely occur not through natural process of survival-of-the-adaquate, but rather by human design.

[Soapy Sam]

Rob- the assumption that a "next step" exists is itelf teleological. I think you don't mean it that way, but I suspect it is the use of phraseology like this which leads to the sort of confusion Ixabert expresses in his original post. Evolution is one of those counter intuitive subjects, where we have to be really careful how we say things.

[Rob Lister]

Originally posted by Soapy Sam
Rob- the assumption that a "next step" exists is itelf teleological. I think you don't mean it that way, but I suspect it is the use of phraseology like this which leads to the sort of confusion Ixabert expresses in his original post. Evolution is one of those counter intuitive subjects, where we have to be really careful how we say things.

When you say that evolution is a counter intuitive subject, you make me doubt my own (intuitive) understanding of it. Certainly, I understand that a teleological evolutionary view is a slightly corrupted one generally, but not as I employed it. Maybe I'm just not understanding you.

[drkitten]

Originally posted by Rob Lister


When you say that evolution is a counter intuitive subject, you make me doubt my own (intuitive) understanding of it. Certainly, I understand that a teleological evolutionary view is a slightly corrupted one generally, but not as I employed it. Maybe I'm just not understanding you.

I think your intuitive understanding is slightly flawed. Specifically, you assume that there is a (unique) "next step" in human evolution, which is at best one possibilty among many. Other possibilities include : the extinction of the species when the Andromeda Strain arrives, further subspeciation into homo morlock and homo eloi (multiple "next steps"), or the apparent cessation of evolution because we are so well-adapted to our environment that no further genetic drift is possible -- or combinations of the above.

[Rob Lister]

Originally posted by drkitten


I think your intuitive understanding is slightly flawed. Specifically, you assume that there is a (unique) "next step" in human evolution, which is at best one possibilty among many.

I assume no such thing. Nor did I imply an assumption, at least as far as non-teleological theory goes. If anything, I implied a clear distinction between a teleological view and evolution.

[drkitten]

Originally posted by Rob Lister


The 'evolution' of humans to the next step might likely occur [...]

[Rob Lister]

The 'evolution' of humans to the next step MIGHT likely occur

[Tricky]

I think the best way to envision this is to think of an evolutionary tree. (Some people call it a "tree of life"). there are multiple branches, some of which then branch further, others which do not change significantly.

What we call an "evolutionary dead end" is a group of organisms that is close to a tip, meaning that no organisms have significantly modified that basic morphology and evolved into other organisms (at least not in large numbers).

Think of it as "close to the tip" as opposed to "close to the trunk"

[Rob Lister]

Originally posted by Tricky
What we call an "evolutionary dead end" is a group of organisms that is close to a tip, meaning that no organisms have significantly modified that basic morphology and evolved into other organisms (at least not in large numbers).[/B]

Have, or will?

[drkitten]

Originally posted by Rob Lister


Have, or will?

In some cases, both. Woolly mammoths, for example. Not only did they not modify their morphology particularly after their appearance, but they also are highly unlikely to do so in the future.

[Tricky]

Originally posted by drkitten
In some cases, both. Woolly mammoths, for example. Not only did they not modify their morphology particularly after their appearance, but they also are highly unlikely to do so in the future.
Exactly. Only extant organisms have the possibility for future branching. But since we do not know the future, the term "evolutionary dead end" most logically must apply only to anything up to the present.

Perhaps some day the environment on earth will change such as to cause an evolutionary boom in sponges.

[Hellbound]

As an off-topic tidbit:

Did you know that you can slice a sponge up, and basically blend it into single cells. If you take this solution and place it in water, the cells will reassociate into a sponge.

Pretty nifty :)

[Soapy Sam]

Rob- Evolution by Natural Selection truly is very complex- You are wise to doubt your understanding- believe me, I doubt mine all the time. If it was simple, there wouldn't be nearly so much debate about it. There are some extremely sharp folk on this forum who are far from 100% convinced that neo-Darwinism has all the answers.

The trouble is that at the beginner level, it all seems quite simple, so folk often think they do understand it. It frequently turns out (years later) that they have ideas which are quite wrong, due to incautious use of "everyday" language in explanations.

That said, your original point is of course that human evolution in future may be less due to Natural Selection than to the same artificial selection we have applied to dogs and now (by GM) to everything else, ourselves included.

I take your point. We would do well though, to remember that Natural Selection will go on working too- both on us and on our parasites, diseases and competitors.

The point of my response was really about use of language. The phrase "the next step" implies that there exists one particular direction in which human evolution is destined to go and that we may shortcut the natural process to get there by technological means. As I said, I don't think that's quite what you meant, but it's a dangerous impression to give to people who may know less about this even than we do, of whom I suspect Ixabert may be one. I'm assuming his is a serious question about natural selection by a newbie to the subject. I'm trying not to confuse him. In process of which I confused you. Sorry for that.

[Dancing David]

I don't know which of SJ Gould's errors applies here more progresivism or determinism.

I say this is an error of progressive thinking, in that 'dead end' implies that an organism is progressing from one state to another.

Regardless of wether you like incremental evolution or radical evolutions, there is no 'progress' from one organism top another, there are adaptive changes and non-adaptive changes, those that can exploit and adaptive change will propagate and those that have non-detrimental changes will propagate.

Evolution is a 'blind' game for the genome, the genome can not predict which changes will benefit or not benefit in a future changed enviroment. So there is no 'progress' there is just change and the potential for adaptation.

Spomges are very old, so are sharks ,my guess is they still evolve.

[Correa Neto]

Originally posted by Rob Lister


Seems to me we could assume that humans are an evolutionary dead-end, at least in the darwin-sense of the word 'evolution'. The 'evolution' of humans to the next step might likely occur not through natural process of survival-of-the-adaquate, but rather by human design.

Lets place the discussions about the exact meaning of "step" apart for a while. I really think the term "natural" deserves an extra ammount of tought.

We improve our survival chances by means of culture and technology. These features were developed by our species because they gave us an evolutionary upper hand. Most species developed claws, deception, shells, horns, etc. to give them an upper hand. We developed culture and technology. So, it was a "natural" development to help us more efficiency in hunting, extracting marrow from bones, catch fishes, getting sexual partners, increase our numbers, etc. What started with stones, twigs and a simple language, now is comprised of several typers of languages, rituals, rockets, microwave owens, genetic engineering, etc.

Therefore, I would say that if we start improving (what we already do) and even re-designing our own bodies, it will still be for us a "natural" process, since it is based on a feature we developed to provide us an evolutionary upper hand.

[edited to add a few tidbits]

[espritch]

A quick google found this link stating that there are 900 fossile genera of sponges and around 5000 living species. That doesn't exactly sound like an evolutionary dead end to me.

http://www.ucmp.berkeley.edu/porifera/porifera.html

[drkitten]

Originally posted by Correa Neto


Lets place the discussions about the exact meaning of "step" apart for a while. I really think the term "natural" deserves an extra ammount of tought.

We improve our survival chances by means of culture and technology. These features were developed by our species because they gave us an evolutionary upper hand. Most species developed claws, deception, shells, horns, etc. to give them an upper hand. We developed culture and technology.

You're certainly correct that at one level, nothing that humans do can truly be called "unnatural." In the context of human evolution, there's a huge difference that should not be blurred between "natural selection" (as usually defined) and "artificial selection" (the sort of manipulation that humans have been doing on their dogs, cattle, and horses and may now be able to do on themselves). Specifically, as was discussed at length earlier, "natural selection" is not a teleological process, and you get yourself into trouble very quickly if you start to think of it this way. There is no "goal" for natural evolution beyond the survival of one's genes, and if it so happens that the valuable genes -- the ones that help our survival -- are the ones that make our antennae longer, we will evolve longer antennae. Until the environment (or our antennae length) changes and those genes are no longer valuable.

Artificial selection, on the other hand, is almost purely goal-directed, where the farmer says to himself, "Darn, I wish I had a breed of cow that gave more milk and didn't die of xenometosis." He then makes sure to breed his cows that give more milk than average and ships the ones that don't give a lot of milk to the local diner. We're now almost at the point where I can clip the "resistence to xenometosis" gene out of a squid and put it into a cow. But the key difference is that there is an end state in the farmer's mind as he's trying to figure out how to cut squid genes apart with a saber saw.....

[Rob Lister]

Originally posted by drkitten


You're certainly correct that at one level, nothing that humans do can truly be called "unnatural." In the context of human evolution, there's a huge difference that should not be blurred between "natural selection" (as usually defined) and "artificial selection" (the sort of manipulation that humans have been doing on their dogs, cattle, and horses and may now be able to do on themselves). Specifically, as was discussed at length earlier, "natural selection" is not a teleological process, and you get yourself into trouble very quickly if you start to think of it this way. There is no "goal" for natural evolution beyond the survival of one's genes, and if it so happens that the valuable genes -- the ones that help our survival -- are the ones that make our antennae longer, we will evolve longer antennae. Until the environment (or our antennae length) changes and those genes are no longer valuable.

Artificial selection, on the other hand, is almost purely goal-directed, where the farmer says to himself, "Darn, I wish I had a breed of cow that gave more milk and didn't die of xenometosis." He then makes sure to breed his cows that give more milk than average and ships the ones that don't give a lot of milk to the local diner. We're now almost at the point where I can clip the "resistence to xenometosis" gene out of a squid and put it into a cow. But the key difference is that there is an end state in the farmer's mind as he's trying to figure out how to cut squid genes apart with a saber saw.....

Beautifully written response.

[Correa Neto]

Well... I was just pointing that, as drkitten said, 'nothing that humans do can truly be called "unnatural" '. No teleology implied.

Sure, evolution can be summarized as survival and reproduction of genes.

In our case, we are using (in ourselves and other species from whom we get benefits) techniches that allow us to improve our survival chances and lifespan. And all of this, in the end, is tied to gene survival and evolution.

Now in our case, I have my doubts if we can not really say that there is not a teleological component in our evolution from the moment we started to realize how the process works.

After all, nowdays, we are actively and counsiously fighting threats to our species (our genes) such as diseases. We can plan ahead and take actions (like creating a vaccine - or genetic treatments - and applying it on the population). The other species from this planets can't do it, if they have or develop some sort of mutation that allow them to face the menace, they survive. if not, go extinct.

And also since we are nowdays studying genetic diseases and gene therapy, again perhaps this could be seen as we are planning ahead our evolution. And this is just natural for us...

I'm not sure if I managed to explain myself correctly. The above reasoning may surely contain a lot of wrong terms usage and also wrong concepts. Please feel free to correct my errors.