Why complex life probably evolved only once

[Ian David]

The universe may be teeming with simple cells like bacteria, but more complex life – including intelligent life – is probably very rare. That is the conclusion of a radical rethink of what it took for complex life to evolve here on Earth.

It suggests that complex alien life-forms could only evolve if an event that happened just once in Earth's history was repeated somewhere else.

<snip>

So if Lane and Martin are right, the textbook idea that complex cells evolved first and only later gained mitochondria is completely wrong: cells could not become complex until they acquired mitochondria.

Simple cells hardly ever engulf other cells, however – and therein lies the catch. Acquiring mitochondria, it seems, was a one-off event. This leads Lane and Martin to their most striking conclusion: simple cells on other planets might thrive for aeons without complex life ever arising. Or, as Lane puts it: "The underlying principles are universal. Even aliens need mitochondria."

More:
http://www.newscientist.com/article/dn18734-why-complex-life-probably-evolved-only-once.html

[exboyfil]

1. Recent conclusion of another book

The Eerie Silence by Paul Davies. The window for developing complex life is really narrow. He identified five events that had to go right for this to happen, and criteria necessary to be in place for it to happen. We used over half our time to get to this point.

We you combine with the speed of light limit, even if technological life develops elsewhere we may never interact with it.

Another cellular key event was the development of chloroplasts which also came from bacteria through endosymbiosis.

[macllyr]

8. happened at least twice on Earth

The fact that endosymbiosis happened several times on earth suggests
that it is not so rare an event....
Proteobacteria -> mitochondria
Cyanobacteria -> Chloroplasts
and other examples I think...

Eukaryotes with symbiotic proto-mitochondria (or plant cells with symbiotic proto-chloroplasts)
were at one time in life history under intense positive selective pressure, and that pressure
was obviously maintained until today.

happened at least twice on earth => can happen elsewhere...

Mac L'lyr

[Igel]

9. But endosymbiosis alone isn't the claim.

The claim is that there's a precise kind of endosymbiosis that is required, and that only happened once.

I don't think it could ever be ruled out that something akin to mitochondria arose several times and the hosts were subsequently outcompeted and driven to extinction.

[macllyr]

10. didn't happen only once

"that precise kind of symbiosis only happened once" : not very likely...

More probably, a very large number of different kind of proto-eukaryote + proto-mitochondria symbiosis happened
simultaneously (in geological terms), and only the most successful one(s) were positively selected, because
they had a better cellular respiration and oxygen usage.

Mac L'lyr

[txlibdem]

14. Are you saying that coconuts migrate?

"Of course not. They could be carried."

It seems to me that there are some pretty complex forms of life surrounding volcanic vents at the bottom of the ocean.

Deep-sea creatures have also been found at the new vents, but the team is not yet revealing any details. "We've seen deep-sea creatures down there, just as at shallower deep-sea vents," says Jon Copley, a marine biologist at the University of Southampton. "But our findings need to be checked by other scientists before we can talk about them."

http://www.newscientist.com/article/dn18759-first-footage-from-worlds-deepest-volcanic-vents.html

What are 'Deep-sea creatures' you ask?

The bizarre inhabitants of the deep include: deep water sharks; devilish-looking dragonfish, that fire beams of red illumination from "lamps" under their eyes; many bioluminescent fish; ancient coelacanths; creeping sea lilies; blood-red squid; an octopus with glow-in-the-dark suckers; bell-shaped, metre-wide jellyfish, snails with armour-plated feet and a deadly jellyfish relative that uses fluorescent tentacles to lure prey.

Perhaps the most dramatic creature is the 13-metre-long giant squid, Architeuthis (recently captured live on film for the first time) and the even more fearsome 15-metre-long colossal squid, never seen alive. Sperm whales and Antarctic sleeper sharks are the only animals equipped to take on these deep-sea prey.

http://www.newscientist.com/article/dn9967-introduction-mysteries-of-the-deep-sea.html

Ours is not the only type of planet where life could exist. Ours is not the only environment even here on Earth where complex multi-cellular life can exist and could have first evolved.

Günter Wächtershäuser proposed the Iron-sulfur world theory and suggested that life might have originated at hydrothermal vents. Wächtershäuser proposed that an early form of metabolism predated genetics. By metabolism he meant a cycle of chemical reactions that produce energy in a form that can be harnessed by other processes.<20>

It has been proposed that amino-acid synthesis could have occurred deep in the Earth's crust and that these amino-acids were subsequently shot up along with hydrothermal fluids into cooler waters, where lower temperatures and the presence of clay minerals would have fostered the formation of peptides and protocells.<21> This is an attractive hypothesis because of the abundance of CH4 and NH3 present in hydrothermal vent regions, a condition that was not provided by the Earth's primitive atmosphere. A major limitation to this hypothesis is the lack of stability of organic molecules at high temperatures, but some have suggested that life would have originated outside of the zones of highest temperature. There are numerous species of extremophiles and other organisms currently living immediately around deep-sea vents, suggesting that this is indeed a possible scenario.

http://en.wikipedia.org/wiki/Hydrothermal_vent#Hydrothermal_origin_of_life

I wouldn't be quick to assume that mitochondria are the only path to complex organisms. The Universe is vast. Our galaxy alone contains over 200 Billion stars (between 200 Billion and 400 Billion) and untold numbers of planets so the odds are about slim to none that our form of life is the only one out there. There may very well be more water-breathers out there in the "galactic federation" than air-breathers. Who knows.

[On the Road]

2. Well, in Fairness

I don't know how you can assume that one cell engulfing another is a "one-off" event. Maybe it's more likely than it seems. But the rationale is very interesting. And the kind of life they predict sounds like those controversial photos of supposed "nanobacteria."

Not being a biologist,though, it's not clear to me how mitochondria provide energy to the cell. I guess this is something to know as a reader of a science publication.

Also linked on the same page, this was quite a good article:

The chaos theory of evolution
Forget finding the laws of evolution. The history of life is just one damn thing after another

http://www.newscientist.com/article/mg20827821.000-the-chaos-theory-of-evolution.html?page=1

[obxhead]

3. Correct me if I'm wrong, but didn't complex life develop several times

on our own planet?

[MineralMan]

4. That seems to me to be a very narrow view of the concept.

If life truly formed here through the process of evolution, as I believe, then the course of events seems pretty inevitable. By defining complex life as only the phenomenon we know about here, the authors limit themselves far too much. I believe their point of view lacks imagination. Here, the lifeforms we know developed in a particular pattern. In other, very different environments, it may develop using different phenomena.

We're strangely shortsighted, we humans.

[Ian David]

5. I predict giant bacteria-people who keep mitochondria as house pets. n/t

[MineralMan]

6. With leashes made of long protein fibers.

:rofl:

[Ian David]

7. Kind of like in The Golden Compass. n/t

[Jim__]

11. People need to read the full article in Nature before attempting to judge this claim.

The article in NewScientist does give us some information on why it considers this complex life very rare. Based on the description in the article, the process requires a specific sequence of events:

To become more complex, cells need more genes and more proteins – and so they need to get bigger. As the volume of any object increases, however, its relative surface area falls: an elephant has less surface area per unit of volume than a mouse, for instance. This is a major problem because simple cells generate the energy they need using the membrane that encloses them.

Lane and Martin calculate that if a bacterium grew to the size of a complex cell, it would run out of juice. It might have space for lots of genes, but it would have barely enough energy to make proteins from them.

I have no idea what the probabilities involved are, but the authors seem to have evidence that the probability of such an event is small. We at least need to read their argument before judging it.

[Ian David]

12. But Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is.

"Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space." -- Douglas Adams

Given that much space, no matter how rare it is, there is still bound to be a lot of it.

Of course, if complex life is very rare, that means that even if there are billions of other intelligent species out there, they could be spread impossibly far apart across really HUGE chasms of space.

[txlibdem]

13. It's times like these that I find myself really missing Dr. Carl Sagan

"Billions and Billions"

R.I.P. learned man of science...