How are sponges an "evolutionary dead end"?

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.
 
Ixabert said:
Does anyone have an answer?
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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.
 
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.
 
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.
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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.
 
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.
 
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.
 
Correa Neto said:
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.
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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.
 
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.
 
Soapy Sam said:
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.
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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.
 
Rob Lister said:


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.
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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.
 
drkitten said:


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.
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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.
 
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"
 
Tricky said:
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]
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Have, or will?
 
Rob Lister said:


Have, or will?
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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.
 
drkitten said:
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.
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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.
 
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