Now I'm wondering what is necessary for an arrangement of single celled organisms to be considered a new multi-cellular animal


(Mark D.) #1

In particular, how does the new arrangement propagate itself through reproduction? At what point does DNA replicate the entire ensemble? It is amazing to imagine these arrangements eventually resulting in tissues and organs in complex animals. At what point do the individual single celled creatures lose their capacity to function independently if separated from the whole?

Does Biologos have any good articles or blog posts covering such questions that might benefit a lay person?


(Phil) #2

good question. I think in this case it involves sharing a cell wall, and I suspect is genetic, probably something to do with stickiness of the cell wall, but I really did not look far enough to know. In any case, I could see where cell clumping would be the first change, and if beneficial, further changes would then follow to elaborate.


(Stephen Matheson) #3

This is a nice place to learn a bit more about questions and answers regarding the evolution of multicellularity.

The piece you posted is IMO unacceptably exaggerated and not worthy of considering. The authors of the actual research article did not claim that they “witnessed in real time a single-celled algae evolve into a multicellular organism.” A hint to the quality and credibility of that piece is the author’s reference to the “George Institute of Technology.”


(Mark D.) #4

Thanks. I’m always happy to upgrade sources!


(Mark D.) #5

That was a fascinating read. Of course much evolution of multi-cellular creatures could take place before the advent of sexual reproduction. But what most fascinates me is how from the merging of two sex cells, the first cell can divide and differentiate into so many different kinds of cells. Just amazing.

Also of interest was the idea that the cause of cancer might ultimately involve the reversion of cells to a single celled life style.


(Mitchell W McKain) #6

These are not quite the same question. Just because an individual is dependent upon a community for survival does not mean the community is a living organism in its own right. It might be probable and the norm but I think there are counterexamples. I would especially be looking at examples where there is no adaptation to specialized roles and thus the dependence on the community may be something as simple as keeping each other warm at night in an especially cold climate, or it could be that the only available game (food source) requires the whole group to bring it down. So I wouldn’t consider such circumstantial reasons for the inability to survive on ones own to be sufficient for making the community a living organism itself.

In general, I would apply the same measures in the definition of life I gave in the other thread and remind people that just because two things are alive does not mean they are equally alive. A community can be far less alive than the individuals which compose it and I certainly think that is the case with humanity and its communities. But lets check the definition for human communities…

  1. Self-organization? Yes the organization of human communities is self-organized and usually arises “organically” in a rather natural unplanned way.
  2. Do they maintain an organization and identity apart from the environment? A good measure of this is the big difference between the internal and external environments. The human community radically changes the requirements for survival for those living as part of it.
  3. Does the organization make changes in its own structure in a way that can be described by the phenomenon of bifurcation? A direct demonstration that this happens would be the greatest challenge and I a quick google hasn’t confirmed that anyone has attempted this. But one of the sure signs that this happens is when you see diversity between different communities which demonstrates that they have made different choices in how they organize themselves.

(Mark D.) #7

On that note aren’t colony insects like ants and bees interesting? Has the specialization advanced to the point where the colony as a whole is best thought of as the “Individual”? After all, no one of its specialized individuals is complete unto itself, though I suppose one could as easily say the queen and drones are individuals in the usual sense and the vast majority of the colony by weight made up of its workers are bioengineered slaves who take care of them. But that is a slippery slope since by that criteria even we are not complete as individuals since one of each sex is required for procreation.


(Mitchell W McKain) #8

I was simply saying that specialization was a signpost not that it was proof either way. So the most I can say is that particular rule-of-thumb is in favor of the ants and bees being examples of a communal organism. The next question is whether the communal organism is more alive than the individual. I don’t know if I have an easy signpost or rule of thumb on that one. Maybe we can ask which is more aware, the individuals or the community. In the case of humanity I would say the individual, but maybe in the case of ants it is the hive. I am thinking about the way in which they identify food for gathering, which is achieved by leaving scent trails. Perhaps the individual ant just follows the trails laid down and really has no idea of where things are personally. Another thing we can ask is how replaceable are the individual? And while the ants are all but indistinguishable, people can be rather unique, and I would say that many in the roles they play no replacement is possible.


(Chris) #9

I watched the video in the link and I didn’t see much multicellularity. I think the article was hyping the results quite a lot. It might have been forming colonies but that’s a long way from being multicellular.

Several years ago there was an experiment that produced multicellularity (colonies?) In yeast cultures. Again a lot of hype. In that case it happened in 7 of 7 cultures suggesting it was a latent trait rather than a novel adaptation.


(Mark D.) #10

Yeah the one I posted was junk. The good one was posted by Mr. Matheson in the third post. Much better.


#11

There are a number of bacteria that undergo terminal differentiation. Here’s a pointer to heterocysts in cyanobacteria. These bacteria create specific cells that fix nitrogen for the rest of the cells in the filaments.


(Mark D.) #12

Thanks. That one was probably a bit over my pay grade but I appreciate the thought.


(Chris) #13

Here’s a good commentary by Jay Wile

No, These Researchers Did Not See a Single-Celled Organism Evolve Into A Multicellular Organism!

Over the course of my scientific career, I have learned that many science journalists are terrible at science and not much better at journalism, so I did what I always do when I read about science in the popular press: I found the scientific article upon which it was based. Not surprisingly, the study didn’t do what the article claims. It did find one interesting result, however.

… , and it is not a new result. Indeed, other researchers noted this behavior four years ago. Interestingly enough, they found that the algae didn’t even need to be in the same species to “team up.” They also saw that when the predator was removed, the algae went back to their single-celled form. Technically, this is called facultative multicellularity , and it is seen in many single-celled organisms. They prefer to live life as individuals, but when they have to, they come together to help one another out.

… Thus, while this study is interesting in the sense that it might have produced a stable colonial version of a single-celled organism , it tells us nothing about how multicellular organisms formed.

Full article


(Mark D.) #14

Certainly what was witnessed wasn’t the transition from a single celled creature to a complex multicellular one. That the single cells persisted living and reproducing as colonial creatures is still interesting, but I agree that it is hard to see how the path toward specialization of cells and complex communication between them arises from there.

Maybe the take away is that single celled forms, or at least those of some algae, show no reluctance to living communally. In fact, I doubt if it makes any sense to impute subjective states of any kind to single celled creatures as it is hard to imagine where any complex cognition could even take place.

In the end those inclined to believe the path taken toward complex multicellularity was entirely natural will continue in that supposition until given a reason to abandon it while those inclined toward creation will do the same for their supposition. Not knowing every step taken toward complex multicellular animals does not privilege either supposition, but neither does it rule it out.


(Randy) #15

All this leads towards interesting questions about the identity of the self, self awareness, etc. :slight_smile:


(Mark D.) #16

Indeed. Those are the questions I find the most interesting too. But the story of how we got from dirt to complex multicellularity is pretty interesting too.


(system) closed #17

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