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srkmish
2014-Dec-31, 05:10 PM
I have been wondering if there are indeed microbes in other planets, will they eventually adapt and evolve into more and more complex beings and finally beings with self awareness such as humans. If the conditions there has made microbe life suitable, can these beings adapt to whatever the conditions are and mutate and start a new pathway for higher lifeforms. Or it can be such that there will never be a higher being due to conditions not favoring such evolution.

Amber Robot
2014-Dec-31, 05:40 PM
I think this is a difficult question to answer because it's not clear to me that we truly understand the conditions necessary for that development.

My feeling is that as long as the local environmental conditions don't disallow it and don't change too rapidly to quench the process, that it would be nearly inevitable. But that's just my opinion.

cjameshuff
2014-Dec-31, 07:15 PM
Life did perfectly fine with single cells for 70% of its history on Earth. That seems to hint that there's not an easy path to developing it, it was a sudden innovation rather than the result of a predictable chain of small improvements. I suspect the fate of a lot of lifebearing worlds is to never make that step during the period in which they can support life.

Swift
2014-Dec-31, 08:10 PM
As we often say about Q&A...

To elaborate, this section of the forum is for astronomy and space exploration questions with straightforward, generally accepted answers.
This question does not have a straightforward answer, so I've moved the discussion to Life in Space.

IsaacKuo
2014-Dec-31, 09:07 PM
We simply don't know if it is inevitable given sufficient time, but we do know that sufficient time is not inevitable.

Here on Earth, single cell life existed for billions of years before the development of multi-cellular life. There are planets which die within that time frame. An Earth-like world around a star a bit bluer than our own could get swallowed up by its red giant phase before reaching the age at which multi-cellular life evolved here on Earth.

Cougar
2015-Jan-01, 01:25 PM
I have been wondering if there are indeed microbes in other planets, will they eventually adapt and evolve into more and more complex beings....

In my unprofessional opinion, I'd say not necessarily. I've always learned that evolution has no specific goal for life forms to evolve toward, and that would include going from simple to complex. It all depends on the environment that the life forms find themselves in. If there's plenty of food/energy available and no competition for it, there's not much benefit for adaptations, except for incrementally making better use of that energy resource, and such adaptations will eventually have diminishing returns.

Noclevername
2015-Jan-01, 03:25 PM
Evolution is a series of makeshift jury-rigs. Nothing is inevitable.

srkmish
2015-Jan-01, 03:26 PM
Thanks guys. I'm learning so much from this forum

Noclevername
2015-Jan-01, 03:46 PM
Glad to help!

Also, all multi-celled life is made from Eukaryotes (http://en.wikipedia.org/wiki/Eukaryote). These are cells with a nucleus and mitochodria (http://en.wikipedia.org/wiki/Mitochondrion), parts of cells that help use energy more efficiently. Mitochondria have their own separate DNA and are thought to have evolved from lesser cells that became symbiotic and eventually just lost the capacity for independence, so they are accidental passengers. Likewise, the chloroplasts (http://en.wikipedia.org/wiki/Chloroplast) in plant cells may have begun as independent photosynthesizing bacteria.

Noclevername
2015-Jan-01, 03:59 PM
The lack of multi-celled prokaryote (http://en.wikipedia.org/wiki/Prokaryote) organisms seems to indicate that something is required to build multi-celled organisms that prokaryotes don't have. Yet there are still plenty of prokaryote microbes around, so whatever they lack, it isn't necessary for survival.

Spacedude
2015-Jan-01, 04:13 PM
Wasn't it the accumulated waste product (oxygen) of the earliest microbes that led to the evolution of the larger organisms? (or at least that was the result here on the Earth?).

Noclevername
2015-Jan-01, 04:31 PM
Wasn't it the accumulated waste product (oxygen) of the earliest microbes that led to the evolution of the larger organisms? (or at least that was the result here on the Earth?).

Not the earliest, the oxygen catastrophe (http://en.wikipedia.org/w/index.php?title=Great_Oxygenation_Event&redirect=no) was a couple of billion years after life started.

And oxygen did not lead to multi-celled life (plenty of O2-breathing microbes still exist), but it was probably a big contributing factor.

cjameshuff
2015-Jan-01, 05:05 PM
Evolution is a series of makeshift jury-rigs. Nothing is inevitable.

Some things are more likely than others, however. Evolution is essentially an optimization process that iteratively seeks out maxima in a fitness landscape shaped by selection forces, the overall tendency toward improvement of fitness is really just thermodynamics at work, and is as inevitable as the increase of entropy. The same forces can lead to different populations following a similar path through that landscape, such as in the cases of the repeated evolution of eyes, wings, legs, etc. Other times, a major change or chance combination of changes can cause a jump to a completely different part of the landscape...I think the development of multicellularity fits in this category, as well as the development of highly abstract, tool-using intelligence.

And another thing to keep in mind, there may be many regions of that fitness landscape that have never been visited by life on Earth. The process of evolution is good at searching large parameter spaces for good-enough solutions, but it has no insight or foresight and is limited to working with existing populations, so it can easily miss things.



The lack of multi-celled prokaryote (http://en.wikipedia.org/wiki/Prokaryote) organisms seems to indicate that something is required to build multi-celled organisms that prokaryotes don't have. Yet there are still plenty of prokaryote microbes around, so whatever they lack, it isn't necessary for survival.

This isn't necessarily the case. I suspect the greater internal complexity and structure of eukaryotes gives them more freedom to develop the needed self organization to form tissues and organs, but it may also be pure accident that multicellular organisms developed from eukaryotes. There's indications that eukaryotes existed 2.7 billion years ago, which means they existed on Earth as strictly unicellular organisms for nearly twice the length of time that multicellular life has existed. Also, I wouldn't assume the eukaryotic approach is the only possible way to achieve the advantages eukaryotes obtained on Earth, it may again just be that they got them first, and no latecomers were able to displace them.

Swift
2015-Jan-01, 08:56 PM
Excellent post cjameshuff.

And another thing to keep in mind, there may be many regions of that fitness landscape that have never been visited by life on Earth. The process of evolution is good at searching large parameter spaces for good-enough solutions, but it has no insight or foresight and is limited to working with existing populations, so it can easily miss things.

And that's just for Earth. Another planet, with even slightly different starting parameters, may have very different results.

Colin Robinson
2015-Jan-02, 10:31 PM
Wasn't it the accumulated waste product (oxygen) of the earliest microbes that led to the evolution of the larger organisms? (or at least that was the result here on the Earth?).


Not the earliest, the oxygen catastrophe (http://en.wikipedia.org/w/index.php?title=Great_Oxygenation_Event&redirect=no) was a couple of billion years after life started.

Accumulation of the oxygen produced by early microbes such as cyanobacteria was a historical process with several steps. The event sometimes called "the oxygen catastrophe" was just one of those steps.


Some things are more likely than others, however. Evolution is essentially an optimization process that iteratively seeks out maxima in a fitness landscape shaped by selection forces, the overall tendency toward improvement of fitness is really just thermodynamics at work, and is as inevitable as the increase of entropy.

An important point. And this relates to Spacedude's point about oxygen, because increasing free oxygen meant a big change to the thermodynamic framework. It created a situation where there were new niches to fill, some of which were filled by multi-celled organisms.

kzb
2015-Jan-05, 01:11 PM
This was discussed in the massive "why still no alien contact" thread. Starts with post #2143 within that thread.

Like Isaac Kuo says above, it can be argued (as it was by Brian Cox in Human Universe) that because all complex life is evolved from just one cell, and it took billions of years for that original cell to arise, that it was very far from inevitable. This would mean that prokaryotic life can be commonplace, but that complex life is rare, and possibly unique to Earth.

However, it is also possible to argue that the symbiosis event which lead to this cell was an adaptation to conditions, specifically the increasing free oxygen concentration. It was only when conditions were correct that this lifeform would have an evolutionary advantage. If this argument is correct, then it is not the prokaryote/eukaryote transition that is the "great filter". From this reasoning, complex life would be more or less inevitable, as long as you had an oxygen catastrophe to drive it.

Noclevername
2015-Jan-05, 01:24 PM
Is it certain that all multicelled life evolved from one cell?

cjameshuff
2015-Jan-05, 06:44 PM
Is it certain that all multicelled life evolved from one cell?

My recollection was a bit fuzzy. On further investigation, multicellularity actually evolved multiple times, some with prokaryotes, though complex multicellular life only arose six times, all with eukaryotes: http://en.wikipedia.org/wiki/Multicellular_organism#Evolutionary_history

So it appears to be a pretty likely outcome once the conditions are met, though there's no guarantee that they ever will be met on a particular planet, whatever they are.

Further back, all the eukaryotes can in principle be traced back to a single common ancestor that formed a symbiotic relationship with the ancestor of mitochondria, though horizontal gene transfer makes that a bit fuzzy and it predates multicellularity by a wide margin.

kzb
2015-Jan-05, 06:44 PM
Is it certain that all multicelled life evolved from one cell?

That seems to be the case. I'm not absolutely sure why myself, but that is what the proponents of the theory say. I guess there are genetic arguments, particularly from mitochondrial DNA (but I'm only guessing).

Barabino
2015-Jan-05, 08:07 PM
This would mean that prokaryotic life can be commonplace, but that complex life is rare, and possibly unique to Earth.


It`s the point of the book Rare Earth by Peter Ward

http://en.wikipedia.org/wiki/Rare_Earth_hypothesis

Colin Robinson
2015-Jan-05, 08:16 PM
This was discussed in the massive "why still no alien contact" thread. Starts with post #2143 within that thread.

Like Isaac Kuo says above, it can be argued (as it was by Brian Cox in Human Universe) that because all complex life is evolved from just one cell, and it took billions of years for that original cell to arise, that it was very far from inevitable. This would mean that prokaryotic life can be commonplace, but that complex life is rare, and possibly unique to Earth.

However, it is also possible to argue that the symbiosis event which lead to this cell was an adaptation to conditions, specifically the increasing free oxygen concentration. It was only when conditions were correct that this lifeform would have an evolutionary advantage. If this argument is correct, then it is not the prokaryote/eukaryote transition that is the "great filter". From this reasoning, complex life would be more or less inevitable, as long as you had an oxygen catastrophe to drive it.

Even so, you might not have an oxygen catastrophe if the initial composition of the biosphere was different I mean, if the initial balance between hydrogen and oxygen atoms was tilted more in the direction of hydrogen.

After all, the oxygen catastrophe happened because organisms were using the water molecule as a hydrogen source for synthesis of organics. Getting hydrogen out of water is a difficult chemical operation it requires a big input of energy. There would be no evolutionary incentive for an organism to perform such an energy-expensive trick unless other hydrogen-containing molecules (e.g. methane, ammonia, hydrogen sulphide, and free hydrogen itself) were all comparatively scarce.

I think people like Brian Cox underestimate the evolutionary role of thermodynamic factors in general, and the oxygen catastrophe specifically. Still, there may be many worlds where organisms comparable to Earth's prokaryotes have been happily hydrogenating carbon dioxide or acetylene for billions of years without ever having an oxygen catastrophe, and without any of them evolving into something with the complexity of a eukaryote.

Colin Robinson
2015-Jan-05, 09:07 PM
My recollection was a bit fuzzy. On further investigation, multicellularity actually evolved multiple times, some with prokaryotes, though complex multicellular life only arose six times, all with eukaryotes: http://en.wikipedia.org/wiki/Multicellular_organism#Evolutionary_history

The Wikipedia page makes the important point that multi-celled organisms seem to have developed out of colonies of single-celled critters, as members of the colony became specialised for different role... As far as I can see, that page doesn't explain what distinguishes "complex multicellular life" from "multicellularity"...


Further back, all the eukaryotes can in principle be traced back to a single common ancestor that formed a symbiotic relationship with the ancestor of mitochondria, though horizontal gene transfer makes that a bit fuzzy and it predates multicellularity by a wide margin.

Yes, a margin of about one billion years.

cjameshuff
2015-Jan-05, 09:47 PM
The Wikipedia page makes the important point that multi-celled organisms seem to have developed out of colonies of single-celled critters, as members of the colony became specialised for different role... As far as I can see, that page doesn't explain what distinguishes "complex multicellular life" from "multicellularity"...

Organization of differentiated cells into tissues and formation of organs, generally.

kzb
2015-Jan-06, 01:14 PM
Even so, you might not have an oxygen catastrophe if the initial composition of the biosphere was different — I mean, if the initial balance between hydrogen and oxygen atoms was tilted more in the direction of hydrogen.

After all, the oxygen catastrophe happened because organisms were using the water molecule as a hydrogen source for synthesis of organics. Getting hydrogen out of water is a difficult chemical operation — it requires a big input of energy. There would be no evolutionary incentive for an organism to perform such an energy-expensive trick unless other hydrogen-containing molecules (e.g. methane, ammonia, hydrogen sulphide, and free hydrogen itself) were all comparatively scarce.

I think people like Brian Cox underestimate the evolutionary role of thermodynamic factors in general, and the oxygen catastrophe specifically. Still, there may be many worlds where organisms comparable to Earth's prokaryotes have been happily hydrogenating carbon dioxide or acetylene for billions of years without ever having an oxygen catastrophe, and without any of them evolving into something with the complexity of a eukaryote.

You're absolutely right Colin. I should've said oxygen catastrophe "or equivalent". The other thing I left out was time -the star has to live long enough for all this to come about.

Noclevername
2015-Feb-22, 08:46 AM
It`s the point of the book Rare Earth by Peter Ward

http://en.wikipedia.org/wiki/Rare_Earth_hypothesis

Huh! I didn't know this:
Multicellular life, e.g., anaerobic metazoa, can exist without oxygen (despite Ward & Brownlee's now disproven contrary assertion[46] ). Three multicellular species, including Spinoloricus nov. sp. discovered in the hypersaline anoxic L'Atalante basin at the bottom of the Mediterranean Sea in 2010, appear to metabolise with hydrogen instead of oxygen, lacking mitochondria and instead using hydrogenosomes.[47][48]

http://en.wikipedia.org/wiki/Hydrogenosome

EDIT: Oh, wait.
It is nearly universally accepted that Hydrogenosomes evolved from mitochondria. So it may or may not be an alternate path to multicelled life.