Discussion and news about the modern effort to understand the nature of life on Earth, finding planets around other stars, and the search for life elsewhere in the universe

Wednesday, July 14, 2010

Altogether now

The issue of multi-cellular life is very, very interesting. A number of years ago Carl Zimmer wrote a very nice piece discussing how, when, and why microbial life on Earth got to acting in a multi-cellular mode. Interestingly, the organism he talks about is the self-same alga - Volvox - that was the subject of the genetic detective work I mentioned in the last post. What I find so fascinating about all this (hence the sudden flurry of posts), are the broader implications for life elsewhere in the universe. This is also motivation for the kind of hare-brained social gaming experiment I suggested last time.

In astrobiology there is ongoing debate about just how unusual, or not, so-called 'complex' life might be out there in the cosmic deeps. A lot of the discussion got rounded up in Ward & Brownlee's book Rare Earth, where they tried to argue the case for our homeworld, and its biosphere, being particularly special. I couldn't help but feel at the time, and more so now, that this line of reasoning was overly mired in the increasingly archaic view that evolution is this rather inflexible progression towards 'complex' life. I think it underestimates the sheer opportunistic side of biology. We also get so blinkered by the historical and sociological context of the development of evolutionary biology that we come to see 'complex' life as a veritable house of cards. One wrong step, one asteroid too many, one poor mutation, and a planet will be forever bereft of multi-cellular life.

As Zimmer discusses, the transition between single-celled, microbial organisms and multi-cellular life has happened multiple times across different phyla during the Earth's history. It occurs as and when the advantages of being 'big', outweigh the advantages of being 'small' - jolly old natural selection. Now, here's the next bit of wide-eyed speculation [and yes, I know, countless sci-fi tales got there first...]. Does multi-cellularity necessarily mean physical connection? While there is certainly a lot of physics that can be exploited by getting together on a microscopic scale (even quantum entanglement in photosynthesis), there may equally be advantages to remote connection. And, while I really don't want to go all starry eyed here, an informationally nutritious medium like the Internet, could provide just the kind of connectivity such life would require - hooking together the individually sophisticated human microbes. Is the internet part and parcel of the evolution of life on Earth? Well, I might not go quite that far, but could a mechanism of long-distance, but intimate, connection occur in a purely biological system?

Obviously if you're James Cameron and you live on an allegorical moon called Pandora then the answer is yes. But for astrobiology it may not be crazy to relax the rules for what is meant by 'complex' life. The next question would be whether the planet-wide signatures of dispersed multi-cellular life would look any different than those from the types of life we know about.


MarkeD said...

I agree with your starry eyes - that evolution can be used to explain most self-organising systems, not just life, and what you say on the advantages of being 'big' over being 'small' reminds me of a great phrase which I think strikes many chords: selfish individuals beat altruistic individuals, but altruistic groups beat selfish groups.

So the web, if it promotes empathy and cooperation between ourselves as little units should eventually best smaller nation states competing against one another, much the same as our organ's cells cooperate to make individuals, etc etc down the rabbit hole :)

Caleb Scharf said...

Thanks for the comment! I like the phrase/quote - yes this gets into a whole mess of interesting stuff. I think for me the intriguing part is thinking about 'alternative' styles of organism, where the biochemistry may be recognizable, but the functional behavior (and hence response to environment, influence on global chemistry etc etc.) may be quite alien. Ultimately this may be relevant for decoding the limited information we hope to have on terrestrial-type exoplanets.

kurt9 said...

The definition of complex life that makes most sense to me is the Eukaryote. The emergence of such along with mitochondria is speculated to be as result of Hydrogen hypothesis based endosymbiosis. The best non-technical book I read about this is Nick Lanes "Power, Sex, and Suicide, the Story of Mitochondria". If this speculation is correct (and I see no reason to doubt it), complex life life is likely to be incredibly rare in the galaxy (the Earth being the only example of it in our galaxy).

Eniac said...

kurt9: I am curious what the reasoning is that leads from the hydrogen hypothesis to the conclusion that complex life should be rare. Endosymbiosis is common enough. What makes the mitochondrion/eukaryote endosymbiosis so special that it should be rare?