Was The Transition From Unicellular To Multicellular

[Nereid]

So its likely that a planet with life would have just some "dumb" animals?

The Ward and Browlee thesis is that 'a planet with life' would likely have little more than unicellular organisms, and maybe not more than just bacteria (and archaea) - we're talking of carbon-based life here, of the kind we are familiar with; I am unaware that there's been any significant science done on what other kinds of life there might be in the universe.

However, since a) we have only studied 'life' on Earth, b) we've only studied one other body enough to rule out 'life' (the Moon), and c) we know next to nothing about the conditions conducive to life (and how they change) on any planet outside our solar system, any statements about what life would be like on 'a planet' must be almost entirely speculative.

 

[Gold Barz]

Well, we know that animals did evolve on this planet, there are also ALOT of different kinds of them...

What Peter Ward said:

"It has always been assumed that attaining the evolutionary grade we call animals would be the final and decisive step. Once we are at this level of evolution, a long and continuous progression toward intelligence should occur. However, recent research shows that while attaining the stage of animal life is one thing, maintaining that level is quite another. The geologic record has shown that once evolved, complex life is subject to an unending succession of planetary disasters, creating what are known as mass extinction events. These rare but devastating events can reset the evolutionary timetable and destroy complex life while sparing simpler life forms. Such discoveries suggest that the conditions allowing the rise and existence of complex life are far more rigorous than are those for life's formation. On some planets, then, life might arise and animals eventually evolve - only to be soon destroyed by a global catastrophe."

So it seems like evolution of animals is not really that difficult to attain but its harder to maintain...also I think these "rare and devastating events" only sped up our ancestors evolution to intelligence, maybe it might do the same for another species on another planet?

http://www.astrobio.net/news/article239.html

 

[Gold Barz]

Also David Grinspoon makes a great point:

"David Grinspoon: I think it is a mistake to look at the many specific peculiarities of Earth's biosphere, and how unlikely such a combination of characteristics seems, and to then conclude that complex life is rare. This argument can only be used to justify the conclusion that planets exactly like Earth, with life exactly like Earth-life, are rare.

My cat "Wookie" survived life as a near-starving alley cat and wound up as a beloved house cat through an unlikely series of biographical accidents, which I won't take up space describing but, trust me, given all of the incredible things that had to happen in just the right way, it is much more likely that there would be no Wookie than Wookie. From this I do not conclude that there are no other cats (The Rare Cat Hypothesis), only that there are no other cats exactly like Wookie.

Life has evolved together with the Earth. Life is opportunistic. The biosphere has taken advantage of the myriad strange idiosyncrasies that our planet has to offer. Not only that, life has created many of Earth's weird qualities. So it is easy to look at our biosphere, and the way it so cleverly exploits Earth's peculiar features, and conclude that this is the best of all possible worlds; that only on such a world could complex life evolve. My bet is that many other worlds, with their own peculiar characteristics and histories, co-evolve their own biospheres. The complex creatures on those worlds, upon first developing intelligence and science, would observe how incredibly well adapted life is to the many unique features of their home world. They might naively assume that these qualities, very different from Earth's, are the only ones that can breed complexity."

http://www.astrobio.net/news/article239.html

 

[Moonbear]

Also David Grinspoon makes a great point:

"David Grinspoon: I think it is a mistake to look at the many specific peculiarities of Earth's biosphere, and how unlikely such a combination of characteristics seems, and to then conclude that complex life is rare.

The converse would also be true. It would be a mistake to look at the evolution of so many diverse forms of life on this planet and conclude it would also be common elsewhere.

As has already been stated by others here, we have a sample set of ONE. One intelligent species on one planet in one galaxy. Based on a sample of one, you cannot predict ANYTHING about likelihood of something happening again somewhere else. There are no trends we can observe, no patterns, no common sets of conditions that are required.

I think you need to find more credible sources than from people who would try to draw predictions and conclusions about the rest of the universe from their observations of a single planet. One can do no more than hand wave and wildly guess about life in the rest of the universe. There is nothing scientific about that. Likewise, we cannot deny the possibility there is life elsewhere in the universe, but until we observe it, we can't make any predictions whatsoever about it. Our planet could be an aberration for having life, or our galaxy could be an aberration for having so many planets without life.

 

[arildno]

I would like to chime in with Moonbear here:
We lack the evidence as to whether the formation of life is a commonly occurring process, or something extremely rare. We can't make statistics out of a single datum!

My subjective opinion is that there are lots of life in the galaxy, but that's a subjective opinion I hold. It is a belief I've got, but I don't have any reasons for this view that I regard as rock-solid and irrefutable.

 

[Gold Barz]

The converse would also be true. It would be a mistake to look at the evolution of so many diverse forms of life on this planet and conclude it would also be common elsewhere.

As has already been stated by others here, we have a sample set of ONE. One intelligent species on one planet in one galaxy. Based on a sample of one, you cannot predict ANYTHING about likelihood of something happening again somewhere else. There are no trends we can observe, no patterns, no common sets of conditions that are required.

I think you need to find more credible sources than from people who would try to draw predictions and conclusions about the rest of the universe from their observations of a single planet. One can do no more than hand wave and wildly guess about life in the rest of the universe. There is nothing scientific about that. Likewise, we cannot deny the possibility there is life elsewhere in the universe, but until we observe it, we can't make any predictions whatsoever about it. Our planet could be an aberration for having life, or our galaxy could be an aberration for having so many planets without life.

How do you know that intelligence only popped up once in the Milky Way though.

 

[Moonbear]

How do you know that intelligence only popped up once in the Milky Way though.

You're missing the point. We don't know anything about life anywhere other than on Earth (it would be BIG news if someone discovered life somewhere else, just like it was when they thought they had discovered some fossils of microorganisms on Mars). That is why we cannot predict anything about any place else in the universe.

 

[Gold Barz]

Okay, so you can't say its a definate yes or no or how unlikely or likely it is then, but is it okay for me to think that there are other intelligent life on other planets in the galaxy (like arildno), would I be just fooling myself or is it reasonable?

"it would be BIG news if someone discovered life somewhere else, just like it was when they thought they had discovered some fossils of microorganisms on Mars" - When did this happen?

 

[selfAdjoint]

Okay, so you can't say its a definate yes or no or how unlikely or likely it is then, but is it okay for me to think that there are other intelligent life on other planets in the galaxy (like arildno), would I be just fooling myself or is it reasonable?

You could look on it as entertainment, but it has nothing to do with science. Traditionally, "reasonable" includes respect for Occam's Razor, that you don't indulge yourself in believing hypotheses for which there is no evidence.

"it would be BIG news if someone discovered life somewhere else, just like it was when they thought they had discovered some fossils of microorganisms on Mars" - When did this happen?

There was a little fuss a couple of years ago. It didn't pan out.

 

[arildno]

Since the evidence we've actually got is that there exists at least one planet teeming with life, it is not more reasonable to say that this the only planet in the galaxy which exhibits life than to say there might well be others exhibiting life.

 

[Gold Barz]

I agree with arildno, I don't think life or intelligence for that matter is that rare.

Cuase I hate believing in false stuff selfAdjoint, so if I believe in other intelligent aliens in our galaxy, would i be believing in false stuff?

 

[selfAdjoint]

The unknowable is neither true nor false, neither untrue nor unfalse. It's just not knowable in any way. To believe it is not so much wrong as silly. Likewise to BELIEVE there are no intellegent life forms elsewhere in the galaxy, in the absence of any evidence, is also silly.

 

[arildno]

Silly is such a strong word; feel free to believe whatever you like, GoldBarz, as long as you are clear about that what evidence we've got is woefully insufficient to extrapolate from in a scientific manner.

 

[Gold Barz]

Yes...because we have no evidence at all.

So selfAdjoint, then I should not believe in alien civilizations in this galaxy nor I should believe that there arent any alien civilizations in this galaxy? So basically keep an open mind to both possibilites, although I have to admit I find it pretty hard to stomach the possibility of just us being the only civilization in the galaxy.

Another interesting question here is would the essentials we have here on Earth apply to alien civilizations too like:

Food; hunting and gathering
Shelter; building "homes" and other structures

Imagine what alien entertainment would be like, like alien sports or some kind of competition?

 

[Nereid]

Actually, Gold_Barz, we already have some pretty good (say, 99% or even closer to 100%) data ... of a negative kind:
- there is no intelligent life exactly like us Homo sap. (civilizations, late 20th century technology and all) on any planet or moon or asteroid in our solar system (except Earth); why? because we have not found anything that looks like a 'I Love Lucy' TV broadcast or mobile/cellphone traffic (among other things)
- ditto, on planets around stars within ~25 lightyears of us (ditto)
- there are no ecosystems (assemblages of 'life') like the major surface (and near surface) ones on Earth on any moon, asteroid or other planet in our solar system; why? because no other solar system body has 'the right' atmosphere, reflection bands showing chlorophyll, etc

You can refine these statements to varying degrees - and that can be quite good fun - but it doesn't get you very far.

Now here's something you might like to chew on: when we get to do some decent 'fossil hunting' on Mars, will be find that life once existed there? Will the 'fossils' likely be chemical traces (such as those we use to conclude that there was life on Earth at the time of the oldest currently preserved rocks)? microfossils (undifferentiated cells, differentiated cells)? trace fossils (e.g. 'worm burrows')? primative eukaryote-like fossils? ...

If we do find that there was once 'simple life' (similar to Earthly bacteria and archaea) on Mars, would this be a huge surprise to astrobiologists? If we failed to find any such, would that be a huge surprise? In either case, why (not)?

Remember, astrobiologists think they are scientists ... so whatever expectations they have re 'ancient life' on Mars you may assume are pretty firmly based in good science.

 

[arildno]

1.Nereid; you might just as well say that out of 3 possibly life-sustaining planets in our solar system (Venus, Mars, Tellus), one shows an abundance of life.

2. We do not know the proportion between possibly life-sustaining planets and the planets which cannot possibly sustain life (for example gas giants, planets too far from or too close to the star) in any planetary system.
In our system, that proportion is 1/3

3. Current planet detection techniques are biased towards detection of huge gaseous planets close to the mother star; we cannot on basis of these data say anything about the prevalence or rarity of Earth-like planets in the galaxy.

4. This is of course entirely speculative, but the "reasons" here are no less valid (or rather, no more invalid) than what you've given.

 

[Happeh]

Bound to happen?, was it inevitable since multicellular organisms has a lot more advantages than unicellular organisms.

Yes. The motivating intelligence can not do anything with a cell. All a cell does is float. If you want to do anything, you need a more complex structure. Multicellularar was inevitable as were all the other creatures developed by evolution. Intelligence want's to manipulate it's environment.