If motility is really essential to their survival. But is it always that? And was it when multicellularity first evolved? Are there non-motile multicellular organisms today that make a successful living in some niche?
If they occur in developing organisms in the wild, the mechanical pressures and chemical gradients are neither unnatural, nor artificial. Those organisms then naturally produce those physical effects.
Agreed, my main point was that the unnatural mechanical pressures worked better than the naturally occurring selection pressures in creating a novel and sustainable phenotype. When I first read the article about the fungi, the first thing I thought about was how some medical scientists are trying to use mechanical pressures for tissue engineering, so that is how I discovered the physics paper, about the same subject.
It’s not clear what you mean by worked better here. One species of organism (Saccharomyces) when subject to settling speed selection was “better” (by what measure?) than some other species (Chlorella) when subject to predation selection? Okay, but what conclusion are we supposed to draw from that?
- Naturally occurring evolution effectively is an evolutionary algorithm.
- Some software evolutionary algorithms work better than others.
- No-one has said that natural evolution works better than software evolutionary algorithms.
- Don’t pay any attention to the blather of ‘ID theorists’.
I can’t draw any hard conclusions from the available data, since it is so limited, but there does seem to be a pattern. Many protists that we think of as being unicellular seem to actually be facultatively unicellular, able to switch between unicellular individuals and multicellular colonies depending on environmental conditions.
So placing them under environmental conditions where they can become multicellular doesn’t harm them so long as that condition doesn’t become permanent, since there are advantages to being able to be both unicellular and multicellular. Trapping them in the multicellular condition limits the options of such organisms in ways that make it more difficult for them to survive. I wouldn’t claim it as any sort of final conclusion, just an observation.
How do you distinguish between already having the ability to switch to a different behavior, from evolving that behavior due to a particular selection pressure over multiple generations?
You appear to be saying the examples you linked above of evolved multicellularity aren’t actually evolved multicellularity, but rather that the organisms were already intrinsically capable of switching to a multicellular phenotype without any evolutionary change occurring. Is that what you are saying, and if it is, how did you determine this?
Gravity was the selective force in the yeast experiment and there is nothing unnatural about it.
We live on a planet whose gravitational impact is significant on the denizens who inhabit it, so it’s ridiculous to believe gravity cannot act as a selective force in some scenario.
For example, gravity can act as a selective force on seeds of varying sizes. Larger seeds are not easily dispersed and are more likely to get eaten if their predators live nearby, and vice versa for smaller seeds. The same plays out in the spread of respiratory pathogens: SARS-CoV-2 particles in large droplets don’t travel too far due to gravity making it an important selective force in the evolution of the virus.
Its true that centrifugation does not take place in nature, but gravitational selection does and it ensured that those clusters persisted once they emerged.
Mutations (the only source of ‘within-cluster’ genetic variation) and some selective force (gravity) led to the evolution of multicellularity in the yeast experiment.
Did you read the C . reinhardtii paper well? It seems you missed this part.
It is obvious there was nothing temporary about the emergence of multicellularity in the strains of C . reinhardtii that evolved it.
Your conjecture is falsified.
Agreed, but on a 2nd reading I’m not taking @Geremy to be saying that gravity plays no part in selection. I think, trying to be charitable, that he’s really just saying that the type of settling speed-dominated selection used in the yeast experiment, is unlikely to work in a wild-type setting.
I’m not persuaded of the truth of such a claim myself, as I can at least conceive of environmental circumstances where the ability of an organism to settle quickly out of a turbulent stream or current might help prevent it from being carried further to a more hostile environment.
I agree, but he should look at the bigger picture, which is that some selective pressure (gravity or predation) and random mutations can drive the evolution of multicellularity, easily.
My thoughts too. It may not exactly match the centrifugation process, but it can be pretty close to it.
ID/creationist: Scientists can’t show evolution occurring in the lab.
Evolutionist: Actually we can. Look at this experiment.
ID/creationist: That doesn’t count because it happened in a lab.
Evolutionist: Good grief.
Actually, scientists and the protists protists in the experiments have to different objectives. The objective of the C. reinhardtii algae is to survive not evolve in ways that threaten it’s survival. So let’s carefully compare three papers that talk about the C. reinhartii experiments in order to make sure we have the proper context.
First, it has also been known for many years before the above experiment that sometimes C. reinhardtii algae forms colonies very much like the ones produced in the experiment, as another much older study explained:
Despite the fact that Chlamydomonas species are known for their ability to produce gelatinous and palmelloid stages (Van den Hoek et al. 1995), rather limited studies have been undertaken to investigate this phenomenon. Often such palmelloid stages are classified in the order Tetrasporales, because they are simply not recognised as Chlamydomonas (Van den Hoek et al. 1995).
The study specifically investigated the role that predators play in in causing the cells to form multicellular clusters protected by membranes, which exists in the species as a known ability, not an never been seen before evolved response. The true extent of what the authors accomplished is explained in a couple sentences where the authors admit:
The ability of wild-type C. reinhardtii to form palmelloids suggests that the founding population in our experiment already possessed a toolkit for producing multicellular structures. However, while the palmelloid condition is expressed facultatively in wild-type C. reinhardtii, the strains that evolved in our experiment are obligately multicellular. Like palmelloids, our evolved multicellular isolates lack motility,suggesting that the ability to express both unicellular and multicellular phenotypes may be optimal when predation pressure varies over time31
So the principle difference between what is found in nature and what was evolved in the lab is that natural palmelloid algae temporarily lack motility, while the evolved palmelloid algae rapidly lost the ability to move on a permanent basis. If this mutation occurs in nature it would likely result in the death of the colony. Here is how another study that specifically studied the mutant algae produced in the above experiment explains it:
In our experiments, populations were evolved in illuminated incubators with ample nutrients obviating the need for photo- or chemotaxis. This process therefore allows multicellular colonies to settle and survive without selection for motility. Thus, while our evolved multicells thrive in a laboratory environment, their immobility would likely place them at a strong fitness disadvantage in nature…
By examining the motility phenotype of newly evolved multicellular Chlamydomonas we have uncovered a trade-off that arises from their novel morphology. However, because flagellar structure and function are unchanged, and unicellular propagules remain phototactic, barriers to the subsequent evolution of externalized flagella and coordinated movement in multicells may not be too high to overcome in the laboratory. Multiple, and possibly sequential, selective pressures are likely required to experimentally evolve naturally viable multicellular algal clusters.
So any claim to have watched the rapid evolution of multicellular organisms from unicellular organisms, is contradicted by two observations:
- The organisms never were obligate unicellular organisms, but rather organisms that can cycle between both multicellular clusters and unicellular individuals whenever environmental conditions permit.
- By creating an environment of constant longterm predation that permanently trapped the organisms in just the multicellular stage, the researchers caused the organism to be completely dependent on their intelligently designed artificial environment to survive. Such organisms would most likely die in a natural environment if a similar environmental condition developed naturally, and thus aren’t in anyway demonstrating that the rapid evolution of obligate multicellular life from transiently multicellular life is possible in nature.
So my observation patiently still awaits falsification
I doubt the protists are sufficiently aware to have objectives.
I agree, but the same thing could be said for you and me when we were embryos. Yet we hit one developmental milestone after another, almost as if it was a list of goals to be accomplished, interesting isn’t it?
Yes, but not in the way you seem to think.
Microbes don’t have objectives, humans do.
You are clearly confused. In the 2019 paper on the evolution of multicellularity by C . reinhardtii, some strains formed colonies and others became truly multicellular. You are obviously conflating both events.
Again you are confused. What evolved wasn’t palmelloid algae. Palmelloid algae consists of aggregates or colonies of algae. What evolved was multicellular algae, which is distinct from algae colonies. I suggest you take your time to read the paper, so that you stop making this sort of mistakes.
This is dead wrong. Wild type C . reinhardtii can switch between unicellular and palmelloid forms in response to predation. They don’t become multicellular. It was in that experiment that some strains of C . reinhardtii evolved simple multicellularity, which has been maintained till date. Slow down and read the paper.
This is still largely bunk. C . reinhardtii is naturally preyed on by other organisms. What the researchers did was recreate that situation in the lab and it led to the evolution of multicellularity which is just mind-blowing.
The strains of C . reinhardtii which evolved multicellularity did so because of predation by their natural predators and not due to being placed in an “intellegently designed artificial environment”.
You hypothesis (not observation) was falsified because there was no reversal to the unicellular state (which happens in wild type palmelloid algae). Remember your initial claim and my response afterwards:
Hmmm. I wouldn’t be so sure. We just might suffer under very convincing illusions that we have objectives.
Hello Geremey and Welcome!
Thanks for the link to an interesting article. My own limited experience with GAs is they are good at what they do, but getting them to do what you want is not trivial. It’s also easy to specify a problem that is either not feasible, or requires intermediate steps that have not been specified. For example, either a Boeing 747 is not in the class of things which can evolve, or it first requires evolution of an intelligent species in need of air transportation to build one for you.
Practically speaking we can set goals for ourselves. I can’t say the same about the E . coli in my gut.