How did multicellular life evolve?

February 5, 2015 by Charles Q. Choi, Astrobiology Magazine, Astrobio.net
Cells of Dictyostelium purpureum, a common soil microbe, streaming to form a multicellular fruiting body. Credit: Natasha Mehdiabadi/Rice University

Scientists are discovering ways in which single cells might have evolved traits that entrenched them into group behavior, paving the way for multicellular life. These discoveries could shed light on how complex extraterrestrial life might evolve on alien worlds.

Researchers detailed these findings in the Oct. 24 issue of the journal Science.

The first known single-celled organisms appeared on Earth about 3.5 billion years ago, roughly a billion years after Earth formed. More complex forms of life took longer to evolve, with the first multicellular animals not appearing until about 600 million years ago.

The evolution of from simpler, unicellular microbes was a pivotal moment in the history of biology on Earth and has drastically reshaped the planet's ecology. However, one mystery about multicellular organisms is why did not return back to single-celled life.

"Unicellularity is clearly successful— are much more abundant than multicellular organisms, and have been around for at least an additional 2 billion years," said lead study author Eric Libby, a mathematical biologist at the Santa Fe Institute in New Mexico. "So what is the advantage to being multicellular and staying that way?"

The answer to this question is usually cooperation, as cells benefitted more from working together than they would from living alone. However, in scenarios of cooperation, there are constantly tempting opportunities "for cells to shirk their duties—that is, cheat," Libby said.

"As an example, consider an ant colony where only the queen is laying eggs and the workers, who cannot reproduce, must sacrifice themselves for the colony," Libby said. "What prevents the ant worker from leaving the colony and forming a new colony? Well, obviously the ant worker cannot reproduce, so it cannot start its own colony. But if it got a mutation that enabled it to do that, then this would be a real problem for the colony. This kind of struggle is prevalent in the evolution of multicellularity because the first multicellular organisms were only a mutation away from being strictly unicellular."

How did multicellular life evolve?
When social amoeba Dictyostelium discoideum starves, it forms a multicellular body. Credit: Scott Solomon

Experiments have shown that a group of microbes that secretes useful molecules that all members of the group can benefit from can grow faster than groups that do not. But within that group, freeloaders that do not expend resources or energy to secrete these molecules grow fastest of all. Another example of cells that grow in a way that harms other members of their groups are , which are a potential problem for all multicellular organisms.

Indeed, many primitive probably experienced both unicellular and multicellular states, providing opportunities to forego a group lifestyle. For example, the bacterium Pseudomonas fluorescens rapidly evolves to generate multicellular mats on surfaces to gain better access to oxygen. However, once a mat has formed, unicellular cheats have an incentive to not produce the glue responsible for mat formation, ultimately leading to the mat's destruction.

To solve the mystery of how multicellular life persisted, scientists are suggesting what they call "ratcheting mechanisms." Ratchets are devices that permit motion in just one direction. By analogy, ratcheting mechanisms are traits that provide benefits in a group context but are detrimental to loners, ultimately preventing a reversion to a single-celled state, said Libby and study co-author William Ratcliff at the Georgia Institute of Technology in Atlanta.

In general, the more a trait makes cells in a group mutually reliant, the more it serves as a ratchet. For instance, groups of cells may divide labor so that some cells grow one vital molecule while other cells grow a different essential compound, so these cells do better together than apart, an idea supported by recent experiments with bacteria.

Ratcheting can also explain the symbiosis between ancient microbes that led to symbionts living inside cells, such as the mitochondria and chloroplasts that respectively help their hosts make use of oxygen and sunlight. The single-celled organisms known as Paramecia do poorly when experimentally derived of photosynthetic symbionts, and in turn symbionts typically lose genes that are required for life outside their hosts.

These ratcheting mechanisms can lead to seemingly nonsensical results. For instance, apoptosis, or programmed cell death, is a process by which a cell essentially undergoes suicide. However, experiments show that higher rates of apoptosis can actually have benefits. In large clusters of yeast cells, apoptotic cells act like weak links whose death allows small clumps of to break free and go on to spread elsewhere where they might have more room and nutrients to grow.

Groups of yeast cells. If key cells die a programmed death, these groups can separate. Credit: E. Libby et al., PLOS Computational Biology

"This advantage does not work for single cells, which meant that any cell that abandoned the group would suffer a disadvantage," Libby said. "This work shows that a cell living in a group can experience a fundamentally different environment than a cell living on its own. The environment can be so different that traits disastrous for a solitary organism, like increased rates of death, can become advantageous for cells in a group."

When it comes to what these findings mean in the search for alien life, Libby said this research suggests that extraterrestrial behavior might appear odd until one better understands that an organism may be a member of a group.

"Organisms in communities can adopt behaviors that would appear bizarre or counterintuitive without proper consideration of their communal context," Libby said. "It is essentially a reminder that a puzzle piece is a puzzle until you know how it fits into a larger context."

A fossil of a 600 million-year-old multicellular organism displays unexpected evidence of complexity. Credit: Virginia Tech

Libby and his colleagues plan to identify other ratcheting mechanisms.

"We also have some experiments in the works to calculate the stability provided by some possible ratcheting traits," Libby said.

Explore further: Geometry, programmed death might have enabled evolution of multicellularity

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Steve 200mph Cruiz
5 / 5 (14) Feb 05, 2015
Here is the Wikipedia article on single celled creatures called Choanoflagellates, which are considered to be close to the last common ancestor of fungi and animals (a common feature between the two is that both have cells with flagellum).

http://Www.wikipe...agellate

Interestingly, some species also have a tendency to stick together and form colonies.
antialias_physorg
5 / 5 (8) Feb 05, 2015
When it comes to what these findings mean in the search for alien life, Libby said this research suggests that extraterrestrial behavior might appear odd until one better understands that an organism may be a member of a group.

Heh. Taken right out of "The Andromeda Strain" (by Michael Crichton, 1969)
viko_mx
1 / 5 (12) Feb 05, 2015
"However, one mystery about multicellular organisms is why cells did not return back to single-celled life"

It is not surprising that some scientists consider it a mystery. These people are immune to rational thought. Must be mortgagors who are attached to their work as serfs. Still would have more success as lawyers. For them a mystery but for other banal explanation simply because life is created, and not emerged by chance. If they start from this position so many mysteries and heavy dilemmas in the scientific world will lapse. But perhaps it will be necessary to optimize the scientific staff in most institutions and it forces many to adhere to the "right" policy and the compromise with conscience has become a standard.
viko_mx
1 / 5 (9) Feb 05, 2015
...cnt
viko_mx
1 / 5 (12) Feb 05, 2015
I can not help you if you do not have eyes for the complexity and harmony relationship of all living organisms on the planet Earth, where every single organism has the exact purpose to maintain bio balance in nature. There is no even one single living organism with excessive or insufficient organs or systems. All organisms are 100% finished, and fully functional for its intended purpose.
viko_mx
1 / 5 (12) Feb 05, 2015
Because you asking funny questions can you dig from the archive the Big Bang movie filmed by accidental witness of this cosmic event? Do you have evidence for it or only bold assumptuions and biased intepretaions which are consistent with widely accepted theories?
viko_mx
1 / 5 (12) Feb 05, 2015
There is no even one living organism on the planet Earth with vestigual organs and systems. It is time to reconcile you information. That you or anyone else do not know what is the function of these organs does not make them redundant.
Тailbone in fact have nothing to do with teil and its function is to hold some important muscles in the pelvis. Appendix is reservoir for beneficial bacteria for man and have protective functions during intestinal infections. It is part of the immune system. People with appendicitis removed suffer more often from stomach and other infections. Nipples are major stimulatory organ in both males and females.
viko_mx
1 / 5 (11) Feb 05, 2015
"That's the theory that makes most sense based on observation. The CMB solidifies that."

How this proves this mythical big bang? CMB and red shift of light coming from the distant galaxies have very banal explanation that have nothing to do with the Big Bang and the expanding universe. But the simple rational explanations do not earn wages in today's materialistic darwinian world.
Graeme
5 / 5 (7) Feb 06, 2015
"why cells did not return back to single-celled life"

Probably they had to sacrifice their reproductive capability to the germ cell line. Otherwise we might have human immune cells living in the sewers digesting bacteria there. Or green cells that broke off leaves eking out an existence like green algae.
viko_mx
1 / 5 (9) Feb 06, 2015
Obviously usual diligently voting partisipants who put a minimum rating of all posts that disagree with the policy of the site do not like and are not interested in the truth even when it is obvious and can be easily verified. Apparently the result of strong feelings and lack of sober thought. At least to make it more intelligently. But on the other hand intelligent and honest person will not engage in such activities.

viko_mx
1 / 5 (9) Feb 06, 2015
As I say before there are no redundant organs or systems in organisms inhabiting this planet. There are gaps in the knowledge for their function, which reduces gradually. Lack of knowledge is not an argument. By the way wiki is not very raliable source for scientific information.
jsdarkdestruction
5 / 5 (10) Feb 06, 2015
Viko, no one cares what a creationist as delusional as you. Why do you come here to preach about your God and bible? I'm waiting for you to prove creationism through the scientific method with scientific evidence. If you've got some great revelation that scientifically is provable as you say I will read it with an open mind and will convert if your evidence is sufficient. No "cause the bible says so" or "its self evident...bla bla bla" crap please.
viko_mx
1 / 5 (8) Feb 06, 2015
It is strange that you spoke on behalf of strangers coming into this site. You see the things as in the devil's mirror. God does not rely on scientific evidence to allow any atheist to seek evidence for its existence. God relies on the belief of the honest man in it and his law who have a sense of harmony in their souls and instinctively discovering the truth. The creation is easy to prove. It is sufficient read the Bible and to comapare historical facts. To show traces of the flood. And to prove that evolution is impossible, which is more than easy. To prove that a lie is a lie when the facts are in your support is much easier than to prove that a lie is the truth, when you can not count on your support facts. Proof of lying is hard work, which may have only temporary success but is doomed to failure in the long run. By the way your nickname is fully in the spirit of the ideology of darwinism. It is not bad to look for evidence of the great myth (bang) and biological evolution.
viko_mx
1 / 5 (8) Feb 06, 2015
But I promise you it's not easy. I have not found such evidencе yet although looking carefully such a long time.
jsdarkdestruction
5 / 5 (8) Feb 06, 2015
But I promise you it's not easy. I have not found such evidencе yet although looking carefully such a long time.

I shall bring only scientific evidence for creation, though for who that has a heart for truth and harmony in his soul is sufficient only the scriptureas evidence.

So you are bringing scientific evidence you've been unable to find despite looking for it for years?
It is not bad to look for evidence of the great myth (bang) and biological evolution.

The way you babble nonsense about it all the time I find it highly unlikely you really feel that way. Nice trying to take the moral high ground but it won't work with us.
viko_mx
1 / 5 (7) Feb 06, 2015
Give me at least one solid evidence for the big bang (myth). Let's look at the details and see whether it can be evidence and to justify why. The very idea of the emergence of the universe from an unknown condition which is only speculation for unknown reason and self organization to the modern high ordered state causes indulgence and compassion. There are no physical law in present that does allow self organization of matter from simplerto more complex structures.
Uncle Ira
4.4 / 5 (7) Feb 06, 2015
my Aunty Caroline got an awesome black Chevrolet Corvette Convertible just by some part-time working online with a macbook... pop over to this web-site:>>>>>> Homejob2.com


Well if Aunty-Caroline-Skippette did so good as that, why you wasting your time here? Did she buy her awesome Chevrolet Corvette Convertible by passing out fliers all over the interweb about the no-home-job-Couyon-Club like you are doing?
Maggnus
5 / 5 (9) Feb 06, 2015
We should stop wasting our time trying to prove something imaginary and never before seen.


Hahahahaha! Oh the irony. Thanks verkle, I needed that.


Hahahahahaa!!! Irony INDEED! Hey verkle, do you know what irony is? Hahahaha that is the best line ever, I think I will save that one for use later!
Maggnus
5 / 5 (7) Feb 06, 2015
Obviously usual diligently voting partisipants who put a minimum rating of all posts that disagree with the policy of the site do not like and are not interested in the truth even when it is obvious and can be easily verified. Apparently the result of strong feelings and lack of sober thought. At least to make it more intelligently. But on the other hand intelligent and honest person will not engage in such activities.



No, it is because people who think for themselves can see through your simplistic and myth-addled commentary and think that you are a creationist simpleton whose every word is dripping with the mythology you think others should believe.

viko_mx
1 / 5 (4) Feb 07, 2015
I have read enough stupid explanations in different sites so I refused to waste my time with them. They try from hundred wells to bring water to demonstrate that the old for cosmology big bang myth is true and rarely have more convincingly impact to the thinking public. When I defend an idea argue unaided and not give sites for reference. I expect the same from interlocutors. It is interesting to see how they thinking.

Incidentally how evolutionists explain the fact that the various earth layers which they believe were formed over hundreds of millions of years each, are with clean flat borders and there is no diffusion between them.
viko_mx
1 / 5 (4) Feb 07, 2015
Does anyone have any idea what is the basic condition which must be met to permit an evolutionary process, if we assume that the first living cell miraculously emerged from inanimate matter?
Vietvet
3.7 / 5 (6) Feb 07, 2015


Incidentally how evolutionists explain the fact that the various earth layers which they believe were formed over hundreds of millions of years each, are with clean flat borders and there is no diffusion between them.


@viko mix has shown once again how dismally ignorant he his, this time it's geology.
Whydening Gyre
5 / 5 (4) Feb 07, 2015
Well, we may never know what started it all - but looking for it is kinda fun...:-)
viko_mx
1 / 5 (4) Feb 07, 2015
@Vietvet

Are you sure? Lets see yor explanation... Show me where I am wrong?

Why the different geological layers have no on their upper surface traces of erosion?

And what is the basic condition that can allows evolution?
viko_mx
1 / 5 (4) Feb 07, 2015

"Well, we may never know what started it all - but looking for it is kinda fun...:-)"

At least to know how life evolved but scienties do not know for now and will do not know in future. Indeed how they would to know when the evolution had never happened? Entropy which causes disorganization is a system always has one foot in front before any opportunity for self organization of matter from simple to more complex forms. And without God who controls of the universe, it would very quickly become in the state of disarray.
Vietvet
3.4 / 5 (5) Feb 07, 2015
@viko mix

@Vietvet

Are you sure? Lets see yor explanation... Show me where I am wrong?

Why the different geological layers have no on their upper surface traces of erosion?

And what is the basic condition that can allows evolution?


Before you mention geology again you need to learn a few basics.

http://www.amazon...18021525
Whydening Gyre
5 / 5 (4) Feb 07, 2015
Does anyone have any idea what is the basic condition which must be met to permit an evolutionary process, if we assume that the first living cell miraculously emerged from inanimate matter?

Space and a couple of elements... Throw in a little gravity and voila - a "laboratory"... a playground, if you will, where anything and everything can happen (and usually does)...
God = G,eometrically O,rganized D,ata.
We humans are here as organisms (organized clumps of data)...
ergo, WE are "god" -
tasked with finding out who and what "we" are...
via science and a little imagination..
viko_mx
1 / 5 (4) Feb 07, 2015
I know more thаn few basics about geology. There is no need to go into the role of the sales representative. Would be more meaningful to explain what I do not know about geology and where I'm wrong. Otherwise, your recommendations are unfounded.

I'm worried that I get no answer to the question what is the basic condition that must be met to become possible the evolutionary process.
Whydening Gyre
5 / 5 (4) Feb 07, 2015
future. Indeed how they would to know when the evolution had never happened? Entropy which causes disorganization is a system always has one foot in front before any opportunity for self organization of matter from simple to more complex forms.


Hell, even entropy "evolves"...

Whydening Gyre
5 / 5 (4) Feb 07, 2015
Incidentally how evolutionists explain the fact that the various earth layers which they believe were formed over hundreds of millions of years each, are with clean flat borders and there is no diffusion between them.


If you don see the diffusion - you're not looking close enough...
viko_mx
1 / 5 (4) Feb 07, 2015
Where are the traces of diffusion and the process of erosion that acted for millions of years? Give supporting photographs and you can answer the question if one layer is applied by natural processes for millions of years, will there be a clear sharp cut and will geological sections appear as you can see them today? Colorado Canyon is a good laboratory for geological research. You can remember how it looks.
Whydening Gyre
5 / 5 (3) Feb 07, 2015
Where are the traces of diffusion and the process of erosion that acted for millions of years? Give supporting photographs and you can answer the question if one layer is applied by natural processes for millions of years, will there be a clear sharp cut and will geological sections appear as you can see them today? Colorado Canyon is a good laboratory for geological research. You can remember how it looks.

Viko,
the layering IS the diffusion process...
And, think about it - the fact that you can see those layers is due to erosion.
My personal conjecture is it layers from the inside to out, thereby bypassing the "erosion factor" you think is necessary to be shown...
However, I'm an artist, not a trained observer of stuff (scientist), so I readily accept I'm probably wrong and will wait for more detailed info to modify my views..
viko_mx
1 / 5 (3) Feb 08, 2015
The layering is diffusion process only in theory of evolution. But real picture that we can see today speaks for the process of very fast layering of the layers in the aquatic environment that is conected with the flood. Therefore we can see sharp borders between each layer which clearly separate them, but not gradient change in the composition and structure of the individual layers.
Vietvet
2.3 / 5 (3) Feb 08, 2015
The layering is diffusion process only in theory of evolution. But real picture that we can see today speaks for the process of very fast layering of the layers in the aquatic environment that is conected with the flood. Therefore we can see sharp borders between each layer which clearly separate them, but not gradient change in the composition and structure of the individual layers.


Like I wrote earlier, @ viko mix doesn't squat about geology.
viko_mx
1 / 5 (3) Feb 08, 2015
@Vietvet

I have no interest in your subjective judgment. It is not good one person to live with the thought that has a monopoly for the truth. Deep misconceptions usualy lead to profound personal conflict sooner or later. I am convinced that you are not able to present scientific arguments in defense of your thesis and ideological impotence makes you engaged in personal attacks. But it is meaningless.
Vietvet
3 / 5 (4) Feb 08, 2015
@Vietvet

It is not good one person to live with the thought that has a monopoly for the truth.

You're right @viko mix, I couldn't agree more. The problem is I rely on evidence while you sanctimoniously and without evidence claim the Bible is the truth. You're the only one here claiming a monopoly for the "truth".
jsdarkdestruction
4 / 5 (4) Feb 08, 2015
Does anyone have any idea what is the basic condition which must be met to permit an evolutionary process, if we assume that the first living cell miraculously emerged from inanimate matter?

Evolution and abiogenesis are two different things. We've told you over and over. It doesn't matter how the first life went from nonliving to living.

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