12 replies to this topic

[The Debatinator]

I once heard that Hydra was a two-celled organism. Is this so?

[Method]

The Debatinator, on May 16 2005, 05:21 PM, said:

I once heard that Hydra was a two-celled organism.  Is this so?

Hydra are a colonial organism made up of two cell types (perhaps 3, can't remember). The same for the Man O'War.

There is an interesting case of a multicellular organism evolving from a single celled organism. This new multicellular organism was classified in a new genus.

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Coloniality in Chlorella vulgaris
Boraas (1983) reported the induction of multicellularity in a strain of Chlorella pyrenoidosa (since reclassified as C. vulgaris) by predation. He was growing the unicellular green alga in the first stage of a two stage continuous culture system as for food for a flagellate predator, Ochromonas sp., that was growing in the second stage. Due to the failure of a pump, flagellates washed back into the first stage. Within five days a colonial form of the Chlorella appeared. It rapidly came to dominate the culture. The colony size ranged from 4 cells to 32 cells. Eventually it stabilized at 8 cells. This colonial form has persisted in culture for about a decade. The new form has been keyed out using a number of algal taxonomic keys. They key out now as being in the genus Coelosphaerium, which is in a different family from Chlorella.

Boraas, M. E. 1983. Predator induced evolution in chemostat culture. EOS. Transactions of the American Geophysical Union. 64:1102.

[The Debatinator]

I'm only bringing this up seeing as most creationists use the point that ther are no 2-5 celled organisms. I want the full facts.

[ret]

I may be making myself sound very stupid, but could you please define "colonial" form? Does it just mean that the creatures live as a colony? If so, that doesn't really seem like a multi-celled organism, it's more like a hive (like bees).

[chance]

The Debatinator

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I'm only bringing this up seeing as most creationists use the point that there are no 2-5 celled organisms. I want the full facts. 

I must admit that I was under the impression that animal life was either single or multicellular, from an evolutionary perspective once the transition to multicellular has been made, why stop at a low number. I was not aware that this was a creationist argument, can you post the full argument?


ret the colonial animal(s) like the Portuguese Man-O-war, is far more integrated than a colony of bees, it looks like a jelly fish, but the individual cells are specialised (stingers, body, etc) and can live independently (for a while). I once heard that the entire organism can be squeezed through a sive then the individual cells reorganise back into the whole!

[ret]

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ret the colonial animal(s) like the Portuguese Man-O-war, is far more integrated than a colony of bees, it looks like a jelly fish, but the individual cells are specialised (stingers, body, etc) and can live independently (for a while). I once heard that the entire organism can be squeezed through a sive then the individual cells reorganise back into the whole!

It sounds to me like it is just a colony, except that the members of the colony are far more inter-dependent than colonies like those of bees. If so, this is hardly a multi-celled organism.

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I must admit that I was under the impression that animal life was either single or multicellular, from an evolutionary perspective once the transition to multicellular has been made, why stop at a low number. I was not aware that this was a creationist argument, can you post the full argument?

The argument, which I consider extremely weak, is as follows: "if evolution is true, there should be multi-celled intermediates that go gradually higher in number, which we don't see." I don't think that is a particullarly fair thing to assert, nor would the existence of such things prove evolution. I don't know all that much about the genetics that make organisms single/multi-celled, so I don't have that much to add here.

[The Debatinator]

Yes, and also that 6-20 celled organisms are parasitic on complicted animals only and that if there were no complicted animals these 6-20 could not have survived. That's the second half I forgot to mention.

[ret]

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Yes, and also that 6-20 celled organisms are parasitic on complicted animals only and that if there were no complicted animals these 6-20 could not have survived.

A slightly better argument, but I would never use it. All it suggests is that the parasites arrived after the complicated animals, which is reasonable after the first argument is defeated.

[chance]

ret, on May 30 2005, 05:50 AM, said:

It sounds to me like it is just a colony, except that the members of the colony are far more inter-dependent than colonies like those of bees. If so, this is hardly a multi-celled organism.
The argument, which I consider extremely weak, is as follows: "if evolution is true, there should be multi-celled intermediates that go gradually higher in number, which we don't see." I don't think that is a particullarly fair thing to assert, nor would the existence of such things prove evolution. I don't know all that much about the genetics that make organisms single/multi-celled, so I don't have that much to add here.

Agreed, It’s not multi-celled in the sense of a 3, 4, or 5 celled organism as requested in the OP.



all, Seems we are all agreed that, '2-5 cells' is not a substantive argument against evolution, yes?

[The Debatinator]

ret, on May 29 2005, 01:17 PM, said:

A slightly better argument, but I would never use it. All it suggests is that the parasites arrived after the complicated animals, which is reasonable after the first argument is defeated.

What I'd like to know is that if evolution is true why don't we see at least some non-parasitic varitions in the 6-20 cell range?

[chance]

The Debatinator, on Jun 3 2005, 09:42 AM, said:

What I'd like to know is that if evolution is true why don't we see at least some non-parasitic varitions in the 6-20 cell range?

Just speculation, but perhaps there is no advantage between a single celled organism and a two celled organism. Advantage is only apparent when cells begin to specialise and perhaps that at about 20 cells.